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Irritable Bowel Syndrome (IBS) and Intestinal Permeability

by luciano

Abstract
Irritable bowel syndrome (IBS) is a complex and multifactorial disorder that cannot be explained by a single pathogenic mechanism. In recent years, increased intestinal permeability (“leaky gut”) has received considerable attention as a potential contributor to IBS pathophysiology. However, current scientific evidence indicates that barrier dysfunction affects only a subset of patients rather than representing a universal feature of the condition. Increased intestinal permeability is more frequently observed in diarrhea-predominant IBS (IBS-D) and post-infectious IBS (PI-IBS), whereas many patients exhibit a structurally intact intestinal barrier. In these cases, symptoms are more accurately attributed to alterations in the gut–brain axis, visceral hypersensitivity, disordered intestinal motility, and gut microbiota dysbiosis. An integrated understanding of these mechanisms is essential to move beyond reductionist models and to guide personalized therapeutic strategies.

Keywords
irritable bowel syndrome, IBS, intestinal permeability, leaky gut, IBS-D, post-infectious IBS, gut barrier, tight junctions, gut-brain axis, visceral hypersensitivity, gut microbiota, functional gastrointestinal disorders, chronic abdominal pain, low-grade inflammation, personalized IBS treatment

1. Introduction
Irritable bowel syndrome (IBS) is one of the most common functional gastrointestinal disorders, characterized by recurrent abdominal pain associated with changes in bowel habits, in the absence of identifiable structural abnormalities. Over the past two decades, the traditional view of IBS as a purely “functional” disorder has been progressively replaced by a more comprehensive model that integrates neurobiological, immune, microbial, and mucosal barrier factors.
Within this evolving framework, increased intestinal permeability—commonly referred to as “leaky gut”—has been proposed as a central mechanism in IBS pathogenesis. While this hypothesis has gained substantial attention, accumulating evidence suggests a more nuanced reality: increased permeability is present only in a subset of IBS patients and does not constitute a defining feature of the syndrome as a whole.

2. Evidence of Altered Intestinal Permeability in IBS
Numerous clinical and experimental studies have assessed intestinal barrier function in IBS using permeability tests (e.g., lactulose/mannitol ratio), urinary and plasma biomarkers, mucosal biopsies, and molecular analyses of tight junction proteins.
Collectively, these studies demonstrate that:
A significant but non-majority proportion of IBS patients exhibits increased intestinal permeability;
Barrier dysfunction is more commonly observed in the colon, although small intestinal involvement may occur in specific subgroups;
Increased permeability is not stable over time and may fluctuate in response to prior infections, dietary factors, psychological stress, and microbiota composition.
These findings indicate that intestinal barrier dysfunction represents an important pathogenic mechanism in IBS, but not an exclusive or universal one.

3. Differences Among IBS Subtypes
The heterogeneity of IBS becomes particularly evident when examining its clinical subtypes:
IBS-D (diarrhea-predominant IBS): This subtype is most frequently associated with increased intestinal permeability. Alterations in tight junction proteins and enhanced immune exposure to luminal antigens have been consistently reported.
Post-infectious IBS (PI-IBS): PI-IBS represents one of the strongest models linking IBS to barrier dysfunction. Following acute gastroenteritis, some patients develop chronic symptoms associated with increased permeability, low-grade mucosal inflammation, and mast cell activation.
IBS-C (constipation-predominant IBS): In most studies, intestinal permeability in IBS-C patients is comparable to that of healthy controls.
IBS-M (mixed subtype): Barrier function appears most consistently preserved in this group.
These differences underscore the absence of a single biological phenotype underlying IBS.

4. Molecular Mechanisms of Barrier Dysfunction
In IBS patients with increased permeability, several structural and functional alterations of the intestinal epithelial barrier have been documented, including:
Reduced expression or disorganization of tight junction proteins such as ZO-1, occludin, and claudins;
Increased paracellular passage of luminal molecules and antigens;
A correlation between the degree of barrier impairment and the severity of abdominal pain.
Loss of epithelial integrity facilitates contact between luminal antigens (bacterial or dietary) and the mucosal immune system, contributing to low-grade inflammatory responses.

5. Interaction Between Intestinal Permeability, Immune System, and Microbiota
In IBS subgroups characterized by barrier dysfunction, increased permeability may initiate a pathogenic cascade involving:
Activation of mast cells and other immune cells within the lamina propria;
Release of inflammatory and neuroactive mediators;
Sensitization of enteric nerve endings.
The gut microbiota plays a central role in this process. Qualitative and functional alterations of microbial communities can both contribute to barrier dysfunction and amplify immune and neural responses. Nevertheless, these mechanisms are not present in all IBS patients, reinforcing the concept of biological heterogeneity.

6. IBS Without Increased Intestinal Permeability
A crucial and often underestimated aspect of IBS is that many patients exhibit a structurally intact intestinal barrier. This is well documented in IBS-C and IBS-M subtypes, but also applies to a proportion of IBS-D patients.
In such cases, the leaky gut model alone is insufficient to explain symptom generation.

7. Alternative Mechanisms Independent of Permeability
7.1 Gut–Brain Axis Dysfunction
IBS is currently classified as a disorder of gut–brain interaction. Altered bidirectional communication between the enteric nervous system and the central nervous system can generate pain, urgency, and bowel habit changes in the absence of mucosal damage.
7.2 Visceral Hypersensitivity
Many IBS patients exhibit a reduced pain threshold to physiological intestinal stimuli. This phenomenon is attributed to:
Peripheral neural sensitization;
Central amplification of nociceptive signaling.
7.3 Altered Intestinal Motility
Disruptions in intestinal motor patterns may account for diarrhea, constipation, or alternating bowel habits without involving epithelial barrier dysfunction.
7.4 Dysbiosis Independent of Barrier Damage
Gut microbiota alterations may influence fermentation, gas production, bile acid metabolism, and neuroendocrine signaling even when intestinal permeability remains normal.

8. Clinical and Therapeutic Implications
Recognizing the heterogeneity of IBS has important clinical consequences:
In IBS-D and PI-IBS patients with documented increased permeability, interventions targeting barrier function (e.g., low-FODMAP diet, microbiota modulation, mucosal protective strategies) may be particularly beneficial;
In patients with normal permeability, therapeutic approaches focused on the gut–brain axis, visceral sensitivity modulation, and stress management are likely more appropriate.
A personalized approach is therefore essential.

9. Conclusions
IBS is a multifactorial and biologically heterogeneous condition. Increased intestinal permeability represents a documented and clinically relevant pathogenic mechanism, but it is not universal. In many patients, symptoms arise from neurofunctional, motor, or microbial alterations in the presence of an intact intestinal barrier.
An integrated perspective allows clinicians and researchers to move beyond reductionist models and to develop more effective diagnostic and therapeutic strategies.
The inflammatory, neurofunctional, microbial, and barrier-related mechanisms discussed here are explored in greater detail in the related articles referenced below.

Commented Bibliographic References (for Further Reading)
1. Camilleri M. et al. – Review on IBS and intestinal barrier function
A critical analysis of permeability alterations across IBS subtypes, emphasizing their non-universality.
2. Bischoff S.C. et al. – Intestinal permeability: mechanisms and clinical relevance
A foundational reference on molecular mechanisms of barrier function and clinical implications.
3. Spiller R., Garsed K. – Post-infectious IBS . Describes PI-IBS as a key model linking low-grade inflammation and increased permeability.
4. Barbara G. et al. – Mast cells and IBS. Seminal work on mast cell involvement in visceral pain and hypersensitivity.
5. Ford A.C. et al. – Systematic reviews on IBS pathophysiology
Integrated overview of microbiota, motility, and gut–brain axis mechanisms.
6. Drossman D.A. – Disorders of gut–brain interaction. A cornerstone reference framing IBS within modern gut–brain interaction paradigms.

The different mechanisms discussed—inflammatory, neuro-functional, microbial, and barrier-related—are examined separately in the related articles.

Human Microbiota and Toxin Metabolism

by luciano

Abstract
The human gut microbiota is a complex ecosystem of microorganisms that plays a central role in digestion, immune function, metabolic regulation, and the handling of dietary and environmental toxins. Through the fermentation of non-digestible carbohydrates and fibers, gut bacteria produce short-chain fatty acids (SCFAs) such as butyrate, acetate, and propionate, which act as key metabolic mediators between the microbiota and the host. These metabolites serve as essential energy substrates for intestinal epithelial cells, support gut barrier integrity, and modulate inflammatory responses and systemic metabolism.
In addition to carbohydrate fermentation, the gut microbiota is involved in the biotransformation of xenobiotics, including environmental toxins, drugs, and food-derived compounds, influencing their bioavailability and toxicity. Conversely, exposure to antibiotics, pollutants, alcohol, and ultra-processed foods can disrupt microbial balance, leading to dysbiosis, increased intestinal permeability, inflammation, and metabolic disorders.
This article explores the bidirectional interactions between the gut microbiota and toxins, the different types of bacterial fermentation (saccharolytic versus proteolytic), and the concept of energetic symbiosis between microbes and the human host. Understanding these mechanisms highlights the crucial role of diet—particularly dietary fiber—in maintaining microbiota functionality, metabolic health, and resilience against toxic and inflammatory challenges.

Keywords
Gut microbiota; Short-chain fatty acids (SCFAs); Dietary fiber; Butyrate; Fermentation; Metabolic health; Inflammation; Gut barrier; Dysbiosis; Toxin metabolism; Gut–liver axis; Energetic symbiosis
1) Human microbiota: definition and role
Definition
The human microbiota is the collection of microorganisms (bacteria, viruses, and fungi) that live on and within the human body, particularly in the gut, and contribute to critical metabolic and immune functions. (Nature)
Main functions
Digestion and fermentation of non-digestible fibers → production of short-chain fatty acids (SCFAs), such as butyrate. (MDPI)
Modulation of energy and glucose metabolism. (Nature)
Maintenance of the immune barrier and protection against pathogens. (Nature)
Involvement in the gut–liver and gut–brain axes. (Atti dell’Accademia Lancisiana)

2) Interactions between the microbiota and toxins
2A – Microbiota → toxins/metabolites
The microbiota:
Ferments dietary fibers [1], producing beneficial metabolites (SCFAs). (MDPI)
Metabolizes xenobiotics (environmental toxins, drugs, additives), influencing their chemical form and toxicity. (MDPI)
Contributes to the intestinal barrier, limiting the absorption of harmful substances. (Atti dell’Accademia Lancisiana)
Recent research:
1. Fan & Pedersen (2020): link the gut microbiota to the metabolism of food-derived compounds and toxins in humans. (Nature)
2. Tu et al. (2020): review on the microbiome and environmental toxicity (concept of gut microbiome toxicity). (MDPI)

2B – Toxins → microbiota
Some agents negatively impact the microbiota:
Antibiotics → intestinal dysbiosis
Pesticides/heavy metals → alteration of microbial diversity
Alcohol and ultra-processed foods → emerging negative effects
Evidence examples:
Environmental and dietary factors can alter microbial balance and increase inflammation. (ScienceDirect)

2C – Effects of dysbiosis
Dysbiosis (microbiota imbalance) may lead to:
Intestinal inflammation
Increased intestinal permeability (leaky gut)
Metabolic disorders (obesity, insulin resistance)
Recent scientific evidence:
Reviews linking microbiota composition to metabolism and human health. (Nature)

3) Factors influencing the microbiota
Factor
Effect
High-fiber diet
↑ diversity and SCFA production (MDPI)
Polyphenols (fruit/vegetables, tea, wine, olive oil)
Positive modulation of the microbial community
Antibiotics
↓ biodiversity, ↑ dysbiosis
Alcohol
May damage the mucosa and promote permeability
Ultra-processed foods
Associated with dysbiosis (mechanisms still under investigation)
Key research:
1. Charnock & Telle-Hansen (2020): effects of fiber on the microbiota and metabolic health. (MDPI)
2. PubMed reviews (2023–2024): fiber and microbiota modulation with clinical implications in metabolic diseases. (PubMed)

4) Toxin elimination: integrated physiological pathways
Liver
Phase I: structural modification of toxins (oxidation)
Phase II: conjugation → increased solubility
Elimination via bile → intestine
The microbiota may modify these metabolites and influence their recirculation
Kidneys
Filter the blood
Eliminate water-soluble toxins through urine
Intestine + microbiota
Excretion of toxins via feces
Physical and metabolic barrier against the absorption of harmful compounds
Lungs and skin
Elimination of CO₂ and volatile compounds
Minor role in the detoxification of more complex molecules

5) Integrative key concepts
SCFAs and health
Products of bacterial fiber fermentation (e.g., butyrate) not only provide substrates for intestinal cells but also modulate inflammation and systemic metabolism. (MDPI)
Microbiota and the gut–liver axis
Microbial metabolites influence hepatic metabolism, with potential effects on toxin handling and lipid metabolism. (Nature)
Diet and metabolic diseases
Microbiota changes associated with low fiber intake are linked to obesity and type 2 diabetes. (PubMed)

Mini-summary
1. The gut microbiota is an ecosystem of microorganisms that supports digestion, immunity, and metabolism; its alteration (dysbiosis) is associated with metabolic diseases. (Nature)
2. Non-digestible dietary fibers are fermented by gut microbes into beneficial compounds (SCFAs). (MDPI)
3. Microbiota and toxins influence each other: the microbiota can degrade or transform xenobiotics, while substances such as antibiotics and pollutants can alter microbial composition. (MDPI)
4. The body eliminates toxins through the liver, kidneys, intestine (with microbiota involvement), lungs, and skin.

Gluten and intestinal inflammation

by luciano

Gluten induces intestinal inflammation not only in celiac individuals but also in healthy ones

Intestinal inflammation is a condition of the gastro-intestinal system that affects a very large and constantly increasing number of people. This condition represents for the individual not only a state of disconfort that affects the quality of life but can – if underestimated or neglected – promote the onset or aggravation of serious illnesses.
An important role but still to be fully explored is played by gluten as it is pro-inflammatory.
The study” The Role of Gluten in Gastrointestinal Disorders: A Review. Sabrina Cenni. Gastrointestinal Disorders: A Review. Nutrients 2023” provides a useful overview of its effectiveness in the prevention and management of these disorderes.

“Abstract: Gluten is only partially digested by intestinal enzymes and can generate peptides that can alter intestinal permeability, facilitating bacterial translocation, thus affecting the immune system. Few studies addressed the role of diet with gluten in the development of intestinal inflammation and in other gastrointestinal disorders. The aim of this narrative review was to analyse the role of gluten in several gastrointestinal diseases so as to give a useful overview of its effectiveness in the prevention and management of these disorders.”

“Introduction. Gluten is a protein mass made of a complex network of gliadins and glutenins, which are proteins rich in glutamines and prolines found in most grains, such as barley, wheat, and rye [1 ,2]. Due to its high-water binding capacity and its consequent malleability and elasticity, gluten induces the formation of viscoelastic membranes, thus determining the proper consistency of dough, which allows it to be processed in bread and other foods [ 3– 5]. The high content of glutamines and prolines in gliadins make them difficult to cleave, making them able to escape degradation from gastric, pancreatic, and intestinal proteolytic enzymes [3, 4]. Therefore, gluten is what remains after the removal of starch, water-soluble proteins, and albumins [1]. In Western countries, the gluten dietary intake is approximately 5 to 20 g per day [3 , 4]. In the last decades, the literature reports an increased number of reactions following a widespread exposure to gluten [ 6]. Gluten-related diseases affect up to 10% of the general population and can be classified as three different disorders: IgE-mediated wheat allergy, Celiac disease (CD), and non-celiac gluten sensitivity (NCGS) [2, 6]. However, there is increasing evidence that gluten can trigger an innate and adaptative immune response responsible for intestinal inflammation [7]. Notably, along with other dietary elements, gluten may contribute to the development of inflammatory intestinal disorders, such as inflammatory bowel disease (IBD), as well as functional gastrointestinal disorders (FGIDs) and concur in symptom exacerbation, although its exact role is still under investigation.”

Gluten and intestinal inflammation.“Inflammation is the natural response of the innate immune system to external stimuli, such as microbial pathogens and injuries [8 ]. When the trigger persists and the immune cells are constantly activated, the inflammatory response may become chronic and self-sustainable [8]. The aetiology of inflammation is clear and easily detectable in some health conditions, while in others it can be difficult to identify [ 8]. The pathogenesis of inflammation is multifactorial. Nevertheless, genetic vulnerability, psychological stress, environmental factors, and some dietary patterns have been described as potentially implicated in the development of inflammatory phenotypes [ 8]. There are at least 50 different types of gliadin epitopes that can have an immunomodulatory and cytotoxic role or that can impact the gut permeating activities [ 8 ]; in fact, some of these can stimulate a pro-inflammatory innate immune response and others can activate specific T cells [8].
Gliadins immune cells’ activation is not only observed in celiac patients, as described by Lammers et al. [9, 10]. Indeed, their study concluded that gliadin induced an inflammatory response and, in particular, an important production of pro-inflammatory cytokines (IL-6, IL- 13, and interferon-gamma) both in Celiac patients and in healthy controls, even if proinflammatory cytokine levels were higher in Celiac patients [9, 10]. Similarly, Harris et al. showed that incubated peripheral blood mononuclear cells (PMBC) obtained from healthy HLA-DQ2 positive individuals produced proinflammatory cytokines, such as IL-23, IL-1beta, and TNF-α, when exposed to gliadin peptides [ 8, 11]. These cytokines’ production was significantly higher in Celiac patients compared to healthy controls [8,11]. Accordingly, Cinova et al., in their case-control study, demonstrated that gliadin could stimulate a substantial TNF-α and IL-8 production by monocytes, principally in celiac patients, but also, to a lesser extent, in healthy control individuals [12]. Gliadin also has an important role in modifying intestinal permeability through the reorganization of actin filaments and the modified expression of junctional complex proteins [ 8,13 ]. As demonstrated by Drago et al. and Lammers et al., gliadin’s binding to the chemokine receptor CXCR3 determines a release of zonulin, an active protein, which compromises the integrity of the intestinal barrier through the rearrangements of actin filaments, ultimately leading to an altered intestinal permeability both in Celiac and non-Celiac patients [ 9, 10, 14 ]. In conclusion, Ziegler et al. and Junker et al. reported that amylase trypsin inhibitors, found in gluten-containing cereals, have the capacity to activate toll-like receptors, thus stimulating the release of inflammatory cytokines and inducing a T-cell immune response in both celiac and non-celiac patients [15,16]”.

Einkorn wheat is the exception in relation to gluten-induced intestinal inflammation

A – Einkorn bread evidenced an anti-inflammatory effect. Integrated Evaluation of the Potential Health Benefits of Einkorn-Based Breads A. Gobetti et al. 2017.

B – Protective effects of ID331 Triticum monococcum. Protective effects of ID331 Triticum monococcum gliadin on in vitro models of the intestinal epithelium. Giuseppe Iacomino et al. (PMID: 27374565 DOI: 10.1016/j.foodchem.2016.06.014 )

Keywords: gluten; inflammatory bowel disease; functional gastrointestinal disorders; celiac disease

Implications of Baker’s Yeast Use in Breadmaking: Fermentative, Structural, and Nutritional Perspectives

by luciano

Abstract
Baker’s yeast (Saccharomyces cerevisiae) is the principal leavening agent in conventional breadmaking. The amount of yeast employed, its metabolic activity before baking, and the characteristics of the cellular residues present in the final product significantly influence the structural, sensory, and nutritional properties of bread. This review provides an in-depth analysis of the effects of excessive yeast usage, the composition of yeast residues after baking, and their impact on product quality and physiological interactions.

A. Effects of Excessive Baker’s Yeast in Dough
Using an excessively high amount of yeast accelerates fermentation, producing adverse effects on dough development and flavor formation.
A.1 Consequences for Dough Fermentation
Rapid CO₂ production: Accelerated fermentation leads to premature saturation of the gluten network.
Overextension of the gluten matrix: Gas expansion may exceed the elastic capacity of the dough, predisposing it to collapse.
Rheological instability: The dough becomes overly gassy, sticky, and challenging to handle.
A.2 Implications for the Final Bread
Aroma and sensory profile: Fast fermentation yields pronounced yeasty or alcoholic notes and reduces aromatic complexity.
Crumb structure: Irregular alveoli and collapsed areas are common outcomes of overproofing.
Crust coloration: Premature depletion of fermentable sugars diminishes Maillard browning, resulting in a paler crust.
Shelf life: Structural weakness accelerates staling.
Controlled, slower fermentation is associated with superior structural and sensory quality.

B. Residual Yeast Components After Baking
During baking, S. cerevisiae cells are rapidly inactivated by heat, remaining in the bread as inert biomass.
B.1 Residual Components
After thermal inactivation, the following remain:
cellular fragments containing proteins, lipids, and nucleotides
cell-wall polysaccharides (β-glucans and mannans)
metabolites produced during pre-baking fermentation (esters, organic acids, aldehydes, higher alcohols)
CO₂ imprints forming the characteristic crumb structure
Nearly all ethanol evaporates during baking.
B.2 Scientific Considerations
Dead yeast cells do not ferment and possess no probiotic activity.
The bread’s microbial profile is unaffected, as baking sterilizes the matrix.
Cellular constituents provide minor nutritional contributions (B-vitamins, amino acids).

C. Excessive Residual Biomass From Overuse of Baker’s Yeast
When yeast is used in quantities above optimal levels, the resulting accumulation of inactive cells and metabolic byproducts measurably affects bread structure and sensory attributes.
C.1 Structural Effects
Dense or slightly gummy crumb: Excess particulate biomass interferes with gluten network dynamics.
Hydration changes: Cell-wall polysaccharides and cellular debris bind additional water, altering dough rheology.
Structural collapse: Typically an indirect consequence of overproofing.
C.2 Effects on Aroma and Flavor
Yeasty or mildly bitter notes: Linked to amino acids, nucleotides, and sulfur-containing compounds released from lysed cells.
Aroma imbalance: Elevated levels of esters and higher alcohols disrupt the natural aromatic profile of bread.
C.3 Nutritional Implications
Excess dead yeast increases concentrations of:
proteins
B-vitamins
minerals
β-glucans and mannans
However, no probiotic effect is conferred, as all cells are inactive.

D. In-Depth Scientific Analysis
D.1 Interaction With the Human Gut Microbiota
Thermally inactivated yeast cells are digested in the gastrointestinal tract like other dietary macromolecules.
They do not exert significant effects on gut microbiota composition.
β-glucans and mannans may have mild prebiotic, but not probiotic, effects.
Most microbiota-relevant transformations in bread are related to sourdough fermentation, which occurs before baking.
D.2 Importance of Accurate Yeast Dosage
Yeast quantity modulates:
Leavening: CO₂ production and gas retention in the gluten network
Aroma formation: Synthesis of esters, aldehydes, alcohols, and organic acids
Dough rheology: Enzymatic modification of starches and proteins
Insufficient yeast:
slow or inadequate rise
dense crumb
increased acidity in sourdough systems
Excess yeast:
overly rapid fermentation
overproofing and structural weakening
reduced aromatic complexity
Professional baking commonly uses 0.5–2% yeast relative to flour weight, adjusted for temperature, hydration, sugar, and salt content.
D.3 Components and Metabolic Byproducts Present After Yeast Death
Post-baking, the following remain integrated within the bread matrix:
pre-formed metabolites (esters, higher alcohols, organic acids)
cellular constituents (amino acids, nucleotides, lipids, minerals, B-vitamins, polysaccharides)
These influence:
aroma (precursors for Maillard reactions)
structure (notable only at high concentrations)
nutritional value (micronutrient contribution)
No metabolic activity occurs after cell death.

Conclusions
The use of baker’s yeast in breadmaking requires precise quantitative control, as fermentation dynamics and final product quality depend heavily on the amount employed. Dead yeast cells in baked bread constitute nutritionally relevant but metabolically inactive biomass, without meaningful effects on microbiota or food safety. Optimal bread quality is achieved through controlled pre-baking fermentation rather than post-baking cellular residues.

Aging of the immune system

by luciano

Overview of the latest research on the aging immune system and its relationship with inflammation

Highlights
1 – Aging is a multifactorial process driven by various intrinsic and extrinsic factors, including genomic instability, telomere shortening (DNA sequence changes) [A], epigenetic alterations, loss of proteostasis, impaired macroautophagy, altered nutrient sensing [B], mitochondrial dysfunction, cellular senescence, stem cell exhaustion, altered intercellular communication, chronic inflammation, and dysbiosis. These factors are closely related to aging, and research has shown that inducing them can accelerate aging, while modifying them can slow, halt, or even reverse the aging process.
2 – Molecules secreted by senescent cells (senescence-associated secretory phenotype SASP [C]) promote chronic inflammation and can induce senescence in normal cells. At the same time, chronic inflammation accelerates the senescence of immune cells, resulting in weakened immune function and the inability to eliminate senescent cells and inflammatory factors, creating a vicious cycle of inflammation and senescence.

3 – Inflammaging [D] (chronic, low-grade, and persistent inflammation) is a recognized hallmark of aging, linked to morbidity and mortality. Inflammaging is so closely intertwined with the aging process that highly accurate aging clocks, predictive of morbidity and mortality, can be constructed using inflammatory markers.

4 – Although coniderable variability in aging exists among individuals, the aging process generally involves chronic inflammation, tissue homeostasis disorders, and dysfunction of the immune system and organ homeostasis disorders, and dysfunction of the immune system and organ functions, functions, readily causing cardiovascular, metabolic, autoimmune, and neurodegenerative diseases associated with aging.

5 – Gerotherapeutic interventions such as caloric restriction, ketogenic diet, or exercise may support healthspan in part by attenuating immune aging through unified immunometabolic mechanisms.

Researches

1 – The immune system offers a window into aging. 2025 Nature Aging.
The immune system permeates and regulates organs and tissues across the body, and has diverse roles beyond pathogen control, including in development, tissue homeostasis and repair. The reshaping of the immune system that occurs during aging is therefore highly consequential.
During aging, the ability of the immune system to efficiently and precisely respond to new antigenic, infectious or neoplastic challenges wanes, and the reactivation and refinement of memory responses falters. One of the earliest manifestations of aging is the involution of the thymus (the site of T cell development), which occurs during puberty. In later life, the immune system increasingly shifts from its homeostatic and protective roles towards a state that is char acterized by heightened proinflammatory activity, with a propensity for autoreactivity. Rather than safeguarding the host, the aged immune system may contribute to systemic dysfunction and pathology.

In this Focus, Nature Aging introduces a series of reviews and opinions that cover recent advances in immune aging. Building on their studies defining immune aging as a driver of organismal aging, Delgado-Pulido and colleagues explore how aging transforms the immune system ‘from healer to saboteur’, and describe the deterioration of protective functions and the acquisition of pathogenic features of the aged adaptive immune system.
Majewska and Krizhanovsky zoom in on one of these protective immune functions that declines with age: namely, the clearance of senescent cells. Through surveying the interactions between senescent and immune cells (which may deteriorate during aging), the authors highlight the role of the aged immune system in facilitating the accumulation and propagation of senescent cells across tissues with age, and thereby fueling tissue dysfunction and disease pathogenesis.
The effects of immune aging on age-related diseases are far-reaching. The fatal consequences of immune aging were demonstrated by impaired infection control during the COVID-19 pandemic. Immune aging has also been implicated in the pathogenesis of non-infectious age-related diseases, including cardiovascular, fibrotic and metabolic diseases, cancer and dementia. Indeed, both peripheral immunity and central neuroinflammation are recognized as contributors to, markers of and potential therapeutic targets in neurodegenerative conditions, and inflammaging is a recognized hallmark of aging linked to morbidity and mortalityrk. Pa and colleagues call attention to resident tissue macrophages as particular culprits of inflammaging and propose that restoring resident tissue macrophages by targeting the niche or myelopoiesis in the bone marrow could attenuate their contribution to tumori- genesis and promote healthy aging.
Inflammaging is so closely intertwined with organismal aging that highly accurate aging clocks, predictive of morbidity and mortality, can be built using markers of inflammation. Tracking individual immune aging trajectories could inform on disease risks as well as contribute to the suits of biological age-predictive biomarkers. However, both aging and the immune system hold considerable complexity and diversity. Franceschi and colleagues survey immune aging clocks through the lens of personalized inflammaging. They highlight that each individual’s unique combination of genetics, lifetime exposures and lifestyle factors results in heterogeneous manifestations of inflammaging, pose that precision measures and interventions should be prioritized, and spotlight a potential role for artificial intelligence in navigating this complexity.
Research on the biological processes of aging is often conducted using model organisms or in vitro models, yet thanks to the ease of access to human blood samples, the immune system offers a window into aging in humans. Immune aging can also be leveraged in clinical trials of aging, by testing the strength of vaccine responses or infection control. Trials that test emerging tech nologies or gerotherapeutic interventions could not only identify strategies to improve immune responses but also stand to inform our understanding of the plasticity of aging in humans and offer important milestones in refining the design of trials conducted with older adults. Discussing strategies to boost immune responses to vaccination in aging, Hofer and colleagues highlight the potential of enhancing vaccines by using gerotherapies to attenuate immune aging.
As well as providing an overview of the hallmarks of immune aging, Kim and Dixit further explore gerotherapeutic interventions, through an immunometabolic lens. They explore how gerotherapeutic interventions such as calorie restriction, ketogenic diet adoption or exercise may sustain healthspan in part through attenuation of immune aging via unified immunometabolic mechanisms. They also highlight adipose as an immunological organ with considerable physiological influence on aging.
Across these articles, the immune system stands out as an early target during aging: the loss of its protective capacities facilitates tissue degeneration and pathology. Weyand and Goronzy, however, highlight the acquisition of autoreactive functions during immune aging, and reflect on recent data that unexpectedly report an increase in autoimmune conditions with age. They propose that autoimmunity during aging constitutes inappropriate immune youthfulness and suggest that wan ing immune activity during aging could be beneficial in calibrating autoreactivity.
As a tractable and targetable window into aging in humans, the aged immune system holds opportunities for translationally valuable discoveries and constitutes a potential broad target to extend healthspan. We are very grateful to the authors and reviewers who have contributed to this issue. Our goal for this Focus has been to stimulate interest and promote cross-pollination of ideas across disciplines. We look forward to supporting immune aging research and sharing exciting findings from this field in the years to come.
References
1. Yousefzadeh, M. J. et al. Nature 594, 100–105 (2021).
2. Desdín-Micó, G. et al. Science 368, 1371–1376 (2020).
3. Bartleson, J. M. et al. Nat. Aging 1, 769–782 (2021).
4. Sarazin, M. et al. Nat. Aging 4, 761–770 (2024).
5. López-Otín, C., Blasco, M. A., Partridge, L., Serrano, M. & Kroemer, G. Cell 186, 243–278 (2023).
6. Sayed N. et al. Nat. Aging 1, 598–615 (2021).
7. Conrad N. et al. Lancet 401, 1878–1890 (2023).
The immune system offers a window into aging. Volume 5; Agosto 2025 Nature Aging. https://doi.org/10.1038/s43587-025-00948-5

2 – Recent Advances in Aging and Immunosenescence: Mechanisms and Therapeutic Strategies. Shuaiqi Wang1 . Cell. 2025

Introduction
Population aging is currently one of the major global challenges [1]. With the intensification of population aging, delaying aging and improving the quality of life for elderly people have become important tasks. Aging is a multifactorial process driven by various intrinsic and extrinsic factors, including genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, disabled macroautophagy, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, altered intercellular communication, chronic inflammation, and dysbiosis [2]. These factors are closely related to organismal aging, and research has shown that inducing them can accelerate aging, while intervening in them can slow down, halt, or even reverse the aging process [2]. Thoroughly studying these aging factors to elucidate the mechanisms of aging can help identify interventions to delay aging, such as caloric restriction, nutritional interventions, and gut microbiota transplantation, as well as clinical treatments for aging-related diseases, eases, including senolytics, stem cell therapy, and antioxidant and anti-inflammatory including senolytics, stem cell therapy, and antioxidant and anti-inflammatory treatments.
These approaches can mitigate aging and aging-related diseases, thereby achieving healthy achieving healthy aging and longevity [3–5].
Among these factors, cellular senescence is a key contributor to organismal aging. Targeting senescent cells (SCs) holds promise for developing novel and practical antiaging therapies [6]. Cellular senescence is an irreversible state of cell cycle arrest caused by varivarious factors, such as DNA damage and telomere shortening [7,8]. Additionally, the process whereby immune system function gradually declines or becomes dysregulated whereby immune system function gradually declines or becomes dysregulated with human aging is known as immunosenescence [E] [9]. Although coniderable variability in aging exists among individuals, the aging process generally involves chronic inflammation, tissue homeostasis disorders, and dysfunction of the immune system and organ homeostasis disorders, and dysfunction of the immune system and organ functions, [2] functions, [2] readily causing cardiovascular, metabolic, autoimmune, and neurodegenerative diseases associated with aging [5,10–13]. Existing research indicates that transplanting SCs into young mice induces bodily dysfunction, while transplanting them into aged mice exacerbates aging and increases the risk of death [6].
This suggests that SCs accelerate organismal aging. The specific reason is that SCs release the senescence-associated secretory phenotype (SASP) into the tissue, promoting chronic inflammation and inducing senescence in surrounding tissue cells and immune cells [14]. SCs and chronic inflammation interact and crosstalk, forming a vicious cycle of inflammation and aging.
Therefore, in-depth research into the key characteristics and underlying mechanisms of cellular senescence, immunosenescence, and inflammation, identifying drug intervention targets, and developing targeted interventions can help mitigate aging and aging-related diseases, thereby promoting healthy aging in the elderly. In recent years, based on the establishment of a series of aging-related cellular and animal models (Table 1), the latest research has revealed the molecular mechanisms of cellular senescence and immunosenescence and the body’s regulation of aging from an immune response perspective.
Moreover, based on new mechanisms, strategies targeting the elimination of SCs have become a promising treatment method for alleviating aging and age-related diseases.
Later, it was discovered that some that small-molecule senolytic senolytic drugs target proteins in cell senescent antiapoptotic pathways (SCAPs) can selectively kill SCs (Figure 1).
Currently, effective, safe, and selective immunotherapy selective approaches targeting SCs are becoming promising a treatment method. Some teams research have teams have already already developed senolytic CAR T cells [19], senolytic vaccines [20], and immune checkpoint blockade (ICB) therapies to achieve the clearance of SCs [21].

Figure 1. 1. Cellular Cellular senescence and senolytics. SCs continuously produce numerous pro-inflammatory senescence and senolytics. SCs continuously produce numerous pro-inflammamolecules and tissue-remodeling molecules, known as the SASP, which further accelerates the aging tory molecules and tissue-remodeling molecules, known as the SASP, which further accelerates the process. Senolytics promote the regeneration of new healthy cells by identifying and clearing SCs. Created with BioRender.com (accessed on 10 May 2024).

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Summary and Prospects
The global issue of population aging is becoming increasingly severe, with elderly individuals being more susceptible to infections and age-related diseases, leading to higher morbidity and mortality rates [5]. Cellular senescence and immunosenescence are closely linked to aging; therefore, this review focuses on immunotherapies targeting aging. It revisits significant recent discoveries in the mechanisms of cellular senescence and immunosenescence that have propelled the development of new treatment paradigms for aging and age-related diseases.
Recent Advances in Aging and Immunosenescence: Mechanisms and Therapeutic Strategies. Shuaiqi Wang1 . Cell. 2025
Department of Immunology, CAMS Key Laboratory T-Cell and Cancer Immunotherapy, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and School of Basic Medicine, Peking Union Medical College, State Key Laboratory of Common Mechanism Research for Major Diseases, Beijing 100005, China; b2023005058@pumc.edu.cn (S.W.); huotong1998@pumc.edu.cn (T.H.); b2022005055@student.pumc.edu.cn (M.L.); s2022005053@student.pumc.edu.cn (Y.Z.); zhangjianmin@ibms.pumc.edu.cn (J.Z.). https://doi.org/10.3390/cells14070499

3 – Chronic Low-Grade Inflammation and Brain Structure in the Middle-Aged and Elderly Adults. 2024
Abstract: Low-grade inflammation (LGI) mainly acted as the mediator of the association of obesity and inflammatory diet with numerous chronic diseases, including neuropsychiatric diseases. However, the evidence about the effect of LGI on brain structure is limited but important, especially in the context of accelerating aging. This study was then designed to close the gap, and we leveraged a total of 37,699 participants from the UK Biobank and utilized inflammation score (INFLA-score) to measure LGI. We built the longitudinal relationships of INFLA-score with brain imaging phenotypes using multiple linear regression models. We further analyzed the interactive effects of specific covariates. The results showed high level inflammation reduced the volumes of the subcortex and cortex, especially the globus pallidus ( β [95% confidence interval] = −0.062 [−0.083, −0.041]), thalamus (−0.053 [−0.073, −0.033]), insula (−0.052 [−0.072, −0.032]), superior temporal gyrus (−0.049 [−0.069, −0.028]), lateral orbitofrontal cortex (−0.047 [−0.068, −0.027]), and others. Most significant effects were observed among urban residents. Furthermore, males and individuals with physical frailty were susceptive to the associations. The study provided potential insights into pathological changes during disease progression and might aid in the development of preventive and control targets in an age-friendly city to promote great health and well-being for sustainable development goals.

Figure 1. Study workflow.Figure 1. Study workflow. We screened 37,699 UK Biobank participants to explore the effects of
We screened 37,699 UK Biobank participants to explore the effects of low-
grade inflammationlow-grade(LGI) oninflammation (LGI) on thd brain system, and the exclusion criteria of our study population
thd brain system, and the exclusion criteria of our study population is
shown in pane (A).is shownAdditionally,in pane we(A).usedAdditionally,the weINFLA-score,used thecharacterizedINFLA-score, bycharacterizedC-reactivebyprotein,C-reactive protein, white blood cell, plateletwhite bloodcounts,cell,andplateletneutrophil-to-lymphocytecounts, and neutrophil-to-lymphocyteratio, to measureratio,andto measurequantifyandthequantify the levels of LGI, and relevantlevels of LGI,informationand relevantas showninformationin paneas shown(B). Asinshownpane (B).inAspaneshown(C),intakingpane (C),influen-taking influential tial factors of LGI intofactorsaccount,of LGIweintofit theaccount,multiplewe fitlinearthe multipleregressionlinearmodelregressioncontrollingmodel forcontrollingcovariatesfor covariates (age, sex, IMD, WHR,(age,healthysex, IMD,lifestyle,WHR, healthyprevalencelifestyle,of hypertension,prevalence of hypertension, diabetes mellitus and stroke)
diabetes mellitus and stroke)
and conducted subgroupand conductedanalysis bysubgroupage, sex,analysisWHR,bymetabolicage, sex,syndrome,WHR, metabolicphysicalsyndrome,frailty. Thephysicalmainfrailty. The results demonstratedmaina significantresults demonstratedassociationa ofsignificantLGI withassociationatrophyofofLGIbrainwithregions,atrophy ofincludingbrain regions,sub- including cortex, frontal lobe,subcortex,temporalfrontallobe, parietallobe, temporallobe andlobe,insulaparietallobe.lobe and insula lobe.

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Conclusions
To sum up, the conceptual and design framework of our investigation is to characterize the associations between LGI and brain imaging phenotypes, thus showing that LGI may lead to subclinical cognitive decline or neuropsychic diseases partly via structural neural pathways. Moreover, our analyses revealed that more significant associations of LGI with the atrophy of brain structure among male or individuals with physical frailty. These findings not only contribute to the evolvement of clinical diagnosis and therapy, but also provide a novel perspective for the development of new preventive strategies, namely, when brain lesions are subclinical and without any apparent clinical sign, inflammatory intervention, such as diet therapy, is an early preventive strategy.
Chronic Low-Grade Inflammation and Brain Structure in the Middle-Aged and Elderly Adults. Yujia Bao et al. School of Public Health, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China; bubble-y@sjtu.edu.cn (Y.B.); c.cctx@sjtu.edu.cn (X.C.); melody321@sjtu.edu.cn (Y.L.); scp-173@sjtu.edu.cn (S.Y.). Nutrients 2024, 16, 2313. https:// doi.org/10.3390/nu16142313