Adipocytes orchestrate the formation of tertiary lymphoid organs in the creeping fat of Crohn's disease affected mesentery

Tertiary lymphoid structures in diseases: immune mechanisms and therapeutic advances

Tertiary lymphoid structures (TLSs) are defined as lymphoid aggregates formed in non-hematopoietic organs under pathological conditions. Similar to secondary lymphoid organs (SLOs), the formation of TLSs relies on the interaction between lymphoid tissue inducer (LTi) cells and lymphoid tissue organizer (LTo) cells, involving multiple cytokines. Heterogeneity is a distinguishing feature of TLSs, which may lead to differences in their functions. Growing evidence suggests that TLSs are associated with various diseases, such as cancers, autoimmune diseases, transplant rejection, chronic inflammation, infection, and even ageing. However, the detailed mechanisms behind these clinical associations are not yet fully understood. The mechanisms by which TLS maturation and localization affect immune function are also unclear. Therefore, it is necessary to enhance the understanding of TLS development and function at the cellular and molecular level, which may allow us to utilize them to improve the immune microenvironment. In this review, we delve into the composition, formation mechanism, associations with diseases, and potential therapeutic applications of TLSs. Furthermore, we discuss the therapeutic implications of TLSs, such as their role as markers of therapeutic response and prognosis. Finally, we summarize various methods for detecting and targeting TLSs. Overall, we provide a comprehensive understanding of TLSs and aim to develop more effective therapeutic strategies.

Preventing fibrosis in IBD: update on immune pathways and clinical strategies

INTRODUCTION

Intestinal fibrosis is a common and serious complication of inflammatory bowel diseases (IBD) driving stricture formation in Crohn's disease patients and leading to submucosal damage in ulcerative colitis. Recent studies provided novel insights into the role of immune and nonimmune components in the pathogenesis of intestinal fibrosis. Those new findings may accelerate the development of anti-fibrotic treatment in IBD patients.

AREAS COVERED

This review is designed to cover the recent progress in mechanistic research and therapeutic developments on intestinal fibrosis in IBD patients, including new cell clusters, cytokines, proteins, microbiota, creeping fat, and anti-fibrotic therapies.

EXPERT OPINION

Due to the previously existing major obstacle of missing consensus on stricture definitions and the absence of clinical trial endpoints, testing of drugs with an anti-fibrotic mechanism is just starting in stricturing Crohn's disease (CD). A biomarker to stratify CD patients at diagnosis without any complications into at-risk populations for future strictures would be highly desirable. Further investigations are needed to identify novel mechanisms of fibrogenesis in the intestine that are targetable and ideally gut specific.

Fibrosis in IBD: from pathogenesis to therapeutic targets

BACKGROUND

Intestinal fibrosis resulting in stricture formation and obstruction in Crohn's disease (CD) and increased wall stiffness leading to symptoms in ulcerative colitis (UC) is among the largest unmet needs in inflammatory bowel disease (IBD). Fibrosis is caused by a multifactorial and complex process involving immune and non-immune cells, their soluble mediators and exposure to luminal contents, such as microbiota and environmental factors. To date, no antifibrotic therapy is available. Some progress has been made in creating consensus definitions and measurements to quantify stricture morphology for clinical practice and trials, but approaches to determine the degree of fibrosis within a stricture are still lacking.

OBJECTIVE

We herein describe the current state of stricture pathogenesis, measuring tools and clinical trial endpoints development.

DESIGN

Data presented and discussed in this review derive from the past and recent literature and the authors' own research and experience.

RESULTS AND CONCLUSIONS

Significant progress has been made in better understanding the pathogenesis of fibrosis, but additional studies and preclinical developments are needed to define specific therapeutic targets.

CT energy spectral parameters of creeping fat in Crohn's disease and correlation with inflammatory activity

OBJECTIVES

Creeping fat is a kind of unique abnormal mesenteric tissue at the sites of diseased bowel of Crohn's disease. By using dual-energy CT enterography, this study aimed to evaluate the feasibility of spectral parameters in the quantitative analysis of mesenteric adipose tissue or creeping fat.

METHODS

In this study, patients with known or suspected Crohn's disease who underwent dual-energy CT enterography from March 1, 2019, to March 31, 2021, were enrolled. Among them, 40 patients with surgery and pathology-proven creeping fat were selected as the creeping fat Crohn's disease group, and 40 normal patients were selected as the control group. The quantitative spectral parameters including the slope of the Hounsfield unit curve, normalised fat-water concentration, normalised fat-iodine concentration, and normalised fat volume fraction at the enteric phases were obtained. Mann-Whitney U test, Kruskal-Wallis H test, and receiver operating characteristic curve analysis were applied to compare quantitative parameters among various groups.

RESULTS

A significant difference was observed in the slope of the Hounsfield unit curve, normalised fat-water concentration, normalised fat-iodine concentration, and normalised fat volume fraction between mesenteric adipose tissue and creeping fat with Crohn's disease at the enteric phase (all p < 0.001). The slope of the Hounsfield unit curve of creeping fat at the enteric phase had a better capability to distinguish inactive and active Crohn's disease (AUC = 0.93, p < 0.001).

CONCLUSION

Dual-energy CT enterography with quantitative spectral parameters is a potentially novel noninvasive tool for evaluating creeping fat in Crohn's disease.

CRITICAL RELEVANCE STATEMENT

Energy spectral parameters of creeping fat in Crohn's disease are significantly different from normal mesenteric adipose tissues and are correlated with inflammatory activity.

KEY POINTS

• Dual-energy CT enterography allows quantitatively assessing creeping fat with spectral parameters. • The creeping fat has distinct spectral parameters to normal mesenteric adipose. • The spectral parameters accurately differentiate active and inactive Crohn's disease.

Tertiary lymphoid structures in autoimmune diseases

Tertiary lymphoid structures (TLSs) are organized lymphoid-like aggregations in non-lymphoid tissues. Tissues with chronic and persistent inflammation infiltration may drive and form ectopic germinal center-like structures, which are very common in autoimmune diseases, chronic infections, and tumor microenvironments. However, the mechanisms governing the formation of TLSs are still being explored. At present, it is not clear whether the formation of TLSs is associated with local uncontrolled immune inflammatory responses. While TLSs suggest a good prognosis in tumors, the opposite is true in autoimmune diseases. This review article will discuss the current views on initiating and maintaining TLSs and the potential therapeutic target in autoimmune diseases.

Creeping fat exhibits distinct Inflammation-specific adipogenic preadipocytes in Crohn's disease

Creeping fat (CrF) is an extraintestinal manifestation observed in patients with Crohn's disease (CD). It is characterized by the accumulation of mesenteric adipose tissue (MAT) that wraps around the intestinal wall. Although the role of CrF in CD is still debated, multiple studies have highlighted a correlation between CrF and inflammation, as well as fibrostenosais of the intestine, which contributes to the worsening of CD symptoms. However, the mechanism underlying the potential role of CrF in the development of Crohn's fibrosis remains an enigma. This study aimed to analyze CrF comprehensively using single-cell RNA sequencing analysis. The data was compared with transcriptomic data from adipose tissue in other disease conditions, such as ulcerative colitis, lymphedema, and obesity. Our analysis classified two lineages of preadipocyte (PAC) clusters responsible for adipogenesis and fibrosis in CrF. Committed PACs in CrF showed increased cytokine expression in response to bacterial stimuli, potentially worsening inflammation in patients with CD. We also observed an increase in fibrotic activity in PAC clusters in CrF. Co-analyzing the data from patients with lymphedema, we found that pro-fibrotic PACs featured upregulated pentraxin-3 expression, suggesting a potential target for the treatment of fibrosis in CrF. Furthermore, PACs in CrF exhibited a distinct increase in cell-to-cell communication via cytokines related to inflammation and fibrosis, such as CCL, LIGHT, PDGF, MIF, and SEMA3. Interestingly, these interactions also increased in PACs of the lymphedema, whereas the increased MIF signal of PACs was found to be a distinct characteristic of CrF. In immune cell clusters in CrF, we observed high immune activity of pro-inflammatory macrophages, antigen-presenting macrophages, B cells, and IgG+ plasma cells. Finally, we have demonstrated elevated IgG+ plasma cell infiltration and increased pentraxin-3 protein levels in the fibrotic regions of CrF in CD patients when compared to MAT from both UC patients and healthy individuals. These findings provide new insights into the transcriptomic features related to the inflammation of cells in CrF and suggest potential targets for attenuating fibrosis in CD.

Creeping Fat in the Pathogenesis of Crohn's Disease: An Orchestrator or a Silent Bystander?

Although the phenomenon of hypertrophied adipose tissue surrounding inflamed bowel segments in Crohn's disease has been described since 1932, the mechanisms mediating the creeping fat formation and its role in the pathogenesis of the disease have not been fully unraveled. Recent advances demonstrating the multiple actions of adipose tissue beyond energy storage have brought creeping fat to the forefront of scientific research. In Crohn's disease, dysbiosis and transmural injury compromise the integrity of the intestinal barrier, resulting in an excessive influx of intraluminal microbiota and xenobiotics. The gut and peri-intestinal fat are in close anatomic relationship, implying a direct reciprocal immunologic relationship, whereas adipocytes are equipped with an arsenal of innate immunity sensors that respond to invading stimuli. As a result, adipocytes and their progenitor cells undergo profound immunophenotypic changes, leading to adipose tissue remodeling and eventual formation of creeping fat. Indeed, creeping fat is an immunologically active organ that synthesizes various pro- and anti-inflammatory cytokines, profibrotic mediators, and adipokines that serve as paracrine/autocrine signals and regulate immune responses. Therefore, creeping fat appears to be involved in inflammatory signaling, which explains why it has been associated with a higher severity or complicated phenotype of Crohn's disease. Interestingly, there is growing evidence for an alternative immunomodulatory function of creeping fat as a second barrier that prevents an abnormal systemic inflammatory response at the expense of an increasingly proliferating profibrotic environment. Further studies are needed to clarify how this modified adipose tissue exerts its antithetic effect during the course of Crohn's disease.

Single-cell Expression Atlas Reveals Cell Heterogeneity in the Creeping Fat of Crohn's Disease

BACKGROUND

Creeping fat (CrF) has been recognized to play a positive role in Crohn's disease (CD) progression, yet the cellular compositions within mesenteric adipose tissue (MAT) and their potential mechanism in CrF formation are poorly understood.

METHODS

Analysis of 10X single-cell RNA sequencing was performed on 67 064 cells from 3 pairs of surgically resected samples of CrF and their uninvolved MAT. The results were validated in another cohort with 6 paired MAT samples by immunofluorescence.

RESULTS

All samples manifested excellent consistency and repeatability in our study, and 10 cell types from the transcriptome atlas, including 20 clusters, were identified. In CrF, a specific vascular endothelial cell subpopulation highly expressing lipoprotein lipase was first identified, with a significantly increased proportion. This vascular endothelial cell subpopulation manifested robust peroxisome proliferator-activated receptor γ (PPARγ) transcription activity and an upregulated PPAR signaling pathway and was involved in lipid metabolism and the antibacterial response. A novel fibroblast subpopulation (FC3) with remarkable GREM1 and RFLNB expression was identified and validated to predominantly accumulate in the CrF. The FC3 was annotated as inflammation-associated fibroblasts, which are characterized by inflammatory responses and the regulation of Smad phosphorylation related to intestinal fibrosis. The trajectory of fibroblasts revealed their pro-inflammatory and profibrotic conversion tendency during CrF formation with corresponding gene dynamics. Additionally, we unprecedently dissected the different origins and functions of 6 macrophage subclusters within the myeloid compartment.

CONCLUSIONS

Our results uncover the cellular heterogeneity in the MAT of CD and the role of these various cellular compositions in CrF development. This comprehensive understanding of CrF provides future directions for in-depth research on and potential targets for MAT-based treatment.

Tertiary Lymphoid Structures (TLSs) and Stromal Blood Vessels Have Significant and Heterogeneous Impact on Recurrence, Lymphovascular and Perineural Invasion amongst Breast Cancer Molecular Subtypes

BACKGROUND

Tertiary lymphoid structures (TLSs) mediate local antitumor immunity, and interest in them significantly increased since cancer immunotherapy was implemented. We examined TLS- tumor stromal blood vessel interplay for each breast cancer (BC) molecular subtype related to recurrence, lymphovascular invasion (LVI), and perineural invasion (PnI).

METHODS

TLSs were quantified on hematoxylin and eosin stain specimens followed by CD34/smooth muscle actin (SMA) double immunostaining for stromal blood vessel maturation assessment. Statistical analysis linked microscopy to recurrence, LVI, and PnI.

RESULTS

TLS negative (TLS-) subgroups in each BC molecular subtype (except to Luminal A) have higher LVI, PnI, and recurrence. A significant rise in LVI and PnI were observed for the HER2+/TLS- subgroup (p < 0.001). The triple negative breast cancer (TNBC)/TLS- subgroup had the highest recurrence and invasion risk which was also significantly related to tumor grade. PnI but not LVI significantly influenced recurrence in the TNBC/TLS+ subgroup (p < 0.001). TLS-stromal blood vessel interrelation was different amongst BC molecular subtypes.

CONCLUSION

BC invasion and recurrence are strongly influenced by TLS presence and stromal blood vessels, especially for HER2 and TNBC BC molecular subtypes.

Disease Association of Anti‒Carboxyethyl Lysine Autoantibodies in Hidradenitis Suppurativa

Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease characterized by recurring suppurating lesions of the intertriginous areas, resulting in a substantial impact on patients' QOL. HS pathogenesis remains poorly understood. An autoimmune component has been proposed, but disease-specific autoantibodies, autoantigens, or autoreactive T cells have yet to be described. In this study, we identify a high prevalence of IgM, IgG, and IgA antibodies directed against Nε-carboxyethyl lysine (CEL), a methylglyoxal-induced advanced glycation end-product, in the sera of patients with HS. Titers of anti-CEL IgG and IgA antibodies were highly elevated in HS compared with those in healthy controls and individuals with other inflammatory skin diseases. Strikingly, the majority of anti-CEL IgG was of the IgG2 subclass and correlated independently with both disease severity and duration. Both CEL and anti-CEL‒producing plasmablasts could be isolated directly from HS skin lesions, further confirming the disease relevance of this autoimmune response. Our data point to an aberration of the methylglyoxal pathway in HS and support an autoimmune axis in the pathogenesis of this debilitating disease.

Tertiary lymphoid structures are critical for cancer prognosis and therapeutic response

Tertiary lymphoid structures (TLSs) are ectopic lymphocyte aggregates that form at sites of chronic inflammation, including cancers, in non-lymphoid tissues. Although the formation of TLSs is similar to that of secondary lymphoid organs, the pathogenic factors leading to TLS formation in cancerous tissues and the mechanisms underlying the role of these structures in the intra-tumoral adaptive antitumor immune response are not fully understood. The presence of TLSs may impact patient prognosis and treatment outcomes. This review examines the current understanding of TLSs in cancers, including their composition and formation as well as their potential to predict prognosis and therapeutic efficacy. We also summarize strategies to induce TLS formation for cancer treatment.

CXCL13-CXCR5 axis: Regulation in inflammatory diseases and cancer

Chemokine C-X-C motif ligand 13 (CXCL13), originally identified as a B-cell chemokine, plays an important role in the immune system. The interaction between CXCL13 and its receptor, the G-protein coupled receptor (GPCR) CXCR5, builds a signaling network that regulates not only normal organisms but also the development of many diseases. However, the precise action mechanism remains unclear. In this review, we discussed the functional mechanisms of the CXCL13-CXCR5 axis under normal conditions, with special focus on its association with diseases. For certain refractory diseases, we emphasize the diagnostic and therapeutic role of CXCL13-CXCR5 axis.

Role of tertiary lymphoid organs in the regulation of immune responses in the periphery

Tertiary lymphoid organs (TLOs) are collections of immune cells resembling secondary lymphoid organs (SLOs) that form in peripheral, non-lymphoid tissues in response to local chronic inflammation. While their formation mimics embryologic lymphoid organogenesis, TLOs form after birth at ectopic sites in response to local inflammation resulting in their ability to mount diverse immune responses. The structure of TLOs can vary from clusters of B and T lymphocytes to highly organized structures with B and T lymphocyte compartments, germinal centers, and lymphatic vessels (LVs) and high endothelial venules (HEVs), allowing them to generate robust immune responses at sites of tissue injury. Although our understanding of the formation and function of these structures has improved greatly over the last 30 years, their role as mediators of protective or pathologic immune responses in certain chronic inflammatory diseases remains enigmatic and may differ based on the local tissue microenvironment in which they form. In this review, we highlight the role of TLOs in the regulation of immune responses in chronic infection, chronic inflammatory and autoimmune diseases, cancer, and solid organ transplantation.

The Complex Relationship Between Microbiota, Immune Response and Creeping Fat in Crohn's Disease

In the last decade, there has been growing interest in the pathological involvement of hypertrophic mesenteric fat attached to the serosa of the inflamed intestinal segments involved in Crohn's disease [CD], known as creeping fat. In spite of its protective nature, creeping fat harbours an aberrant inflammatory activity which, in an already inflamed intestine, may explain why creeping fat is associated with a greater severity of CD. The transmural inflammation of CD facilitates the interaction of mesenteric fat with translocated intestinal microorganisms, contributing to activation of the immune response. This may be not the only way in which microorganisms alter the homeostasis of this fatty tissue: intestinal dysbiosis may also impair xenobiotic metabolism. All these CD-related alterations have a functional impact on nuclear receptors such as the farnesoid X receptor or the peroxisome proliferator-activated receptor γ, which are implicated in regulation of the immune response, adipogenesis and the maintenance of barrier function, as well as on creeping fat production of inflammatory-associated cells such as adipokines. The dysfunction of creeping fat worsens the inflammatory course of CD and may favour intestinal fibrosis and fistulizing complications. However, our current knowledge of the pathophysiology and pathogenic role of creeping fat is controversial and a better understanding might provide new therapeutic targets for CD. Here we aim to review and update the key cellular and molecular alterations involved in this inflammatory process that link the pathological components of CD with the development of creeping fat.

Adipose tissue microenvironments during aging: Effects on stimulated lipolysis

Adipose tissue is a critical organ for nutrient sensing, energy storage and maintaining metabolic health. The failure of adipose tissue homeostasis leads to metabolic disease that is seen during obesity or aging. Local metabolic processes are coordinated by interacting microenvironments that make up the complexity and heterogeneity of the adipose tissue. Catecholamine-induced lipolysis, a critical pathway in adipocytes that drives the release of stored triglyceride as free fatty acid after stimulation, is impaired during aging. The impairment of this pathway is associated with a failure to maintain a healthy body weight, core body-temperature during cold stress or mount an immune response. Along with impairments in aged adipocytes, aging is associated with an accumulation of inflammation, immune cell activation, and increased dysfunction in the nervous and lymphatic systems within the adipose tissue. Together these microenvironments support the initiation of stimulated lipolysis and the transport of free fatty acid under conditions of metabolic homeostasis. However, during aging, the defects in these cellular systems result in a reduction in ability to stimulate lipolysis. This review will focus on how the immune, nervous and lymphatic systems interact during tissue homeostasis, review areas that are impaired with aging and discuss areas of research that are currently unclear.

Tertiary lymphoid structures in cancer

Ectopic lymphoid aggregates, termed tertiary lymphoid structures (TLSs), are formed in numerous cancer types, and, with few exceptions, their presence is associated with superior prognosis and response to immunotherapy. In spite of their presumed importance, the triggers that lead to TLS formation in cancer tissue and the contribution of these structures to intratumoral immune responses remain incompletely understood. Here, we discuss the present knowledge on TLSs in cancer, focusing on (i) the drivers of TLS formation, (ii) the function and contribution of TLSs to the antitumor immune response, and (iii) the potential of TLSs as therapeutic targets in human cancers.

Role of mesenteric component in Crohn’s disease: A friend or foe?

Crohn’s disease (CD) is a complex and relapsing gastrointestinal disease with mesenteric alterations. The mesenteric neural, vascular, and endocrine systems actively take part in the gut dysbiosis-adaptive immunity-mesentery-body axis, and this axis has been proven to be bidirectional. The abnormalities of morphology and function of the mesenteric component are associated with intestinal inflammation and disease progress of CD via responses to afferent signals, neuropeptides, lymphatic drainage, adipokines, and functional cytokines. The hypertrophy of mesenteric adipose tissue plays important roles in the pathogenesis of CD by secreting large amounts of adipokines and representing a rich source of proinflammatory or profibrotic cytokines. The vascular alteration, including angiogenesis and lymphangiogenesis, is concomitant in the disease course of CD. Of note, the enlarged and obstructed lymphatic vessels, which have been described in CD patients, are likely related to the early onset submucosa edema and being a cause of CD. The function of mesenteric lymphatics is influenced by endocrine of mesenteric nerves and adipocytes. Meanwhile, the structure of the mesenteric lymphatic vessels in hypertrophic mesenteric adipose tissue is mispatterned and ruptured, which can lead to lymph leakage. Leaky lymph factors can in turn stimulate adipose tissue to proliferate and effectively elicit an immune response. The identification of the role of mesentery and the crosstalk between mesenteric tissues in intestinal inflammation may shed light on understanding the underlying mechanism of CD and help explore new therapeutic targets.

Drug Targeting of Inflammatory Bowel Diseases by Biomolecules

Inflammatory bowel disease (IBD) is a group of disabling, destructive and incurable immune-mediated inflammatory diseases comprising Crohn’s disease (CD) and ulcerative colitis (UC), disorders that are highly prevalent worldwide and demand a large investment in healthcare. A persistent inflammatory state enables the dysfunction and destruction of healthy tissue, hindering the initiation and endurance of wound healing. Current treatments are ineffective at counteracting disease progression. Further, increased risk of serious side effects, other comorbidities and/or opportunistic infections highlight the need for effective treatment options. Gut microbiota, the key to preserving a healthy state, may, alternatively, increase a patient’s susceptibility to IBD onset and development given a relevant bacterial dysbiosis. Hence, the main goal of this review is to showcase the main conventional and emerging therapies for IBD, including microbiota-inspired untargeted and targeted approaches (such as phage therapy) to infection control. Special recognition is given to existing targeted strategies with biologics (via monoclonal antibodies, small molecules and nucleic acids) and stimuli-responsive (pH-, enzyme- and reactive oxygen species-triggered release), polymer-based nanomedicine that is specifically directed towards the regulation of inflammation overload (with some nanosystems additionally functionalized with carbohydrates or peptides directed towards M1-macrophages). The overall goal is to restore gut balance and decrease IBD’s societal impact.

Tertiary Lymphoid Structures in Cancer: The Double-Edged Sword Role in Antitumor Immunity and Potential Therapeutic Induction Strategies

The complex tumor microenvironment (TME) plays a vital role in cancer development and dramatically determines the efficacy of immunotherapy. Tertiary lymphoid structures (TLSs) within the TME are well recognized and consist of T cell-rich areas containing dendritic cells (DCs) and B cell-rich areas containing germinal centers (GCs). Accumulating research has indicated that there is a close association between tumor-associated TLSs and favorable clinical outcomes in most types of cancers, though a minority of studies have reported an association between TLSs and a poor prognosis. Overall, the double-edged sword role of TLSs in the TME and potential mechanisms need to be further investigated, which will provide novel therapeutic perspectives for antitumor immunoregulation. In this review, we focus on discussing the main functions of TLSs in the TME and recent advances in the therapeutic manipulation of TLSs through multiple strategies to enhance local antitumor immunity.

Implications of lymphatic alterations in the pathogenesis and treatment of inflammatory bowel disease

Inflammatory bowel disease (IBD) is characterized by intense immune dysregulation, gut microbiota imbalance, and intestinal epithelium destruction. Among the factors that contribute to the pathogenesis of IBD, lymphatics have received less attention, hence less studied, characterized, and explored. However, in recent years, the role of the lymphatic system in gastrointestinal pathophysiology continues to be highlighted. This paper examines the implications of lymphatic changes in IBD pathogenesis related to immune cells, gut microbiota, intestinal and mesenteric epithelial barrier integrity, and progression to colorectal cancer (CRC). Therapeutic targets of lymphatics in IBD studies are also presented. Available studies indicate that lymph nodes and other secondary lymphatic tissues, provide highly specialized microenvironments for mounting effective immune responses and that lymphatic integrity plays a significant role in small intestine homeostasis, where the lymphatic vasculature effectively controls tissue edema, leukocyte exit, bacterial antigen, and inflammatory chemokine clearance. In IBD, there are functional and morphological alterations in intestinal and mesenteric lymphatic vessels (more profoundly in Crohn's disease [CD] compared to ulcerative colitis [UC]), including lymphangiogenesis, lymphangiectasia, lymphadenopathy, and lymphatic vasculature blockade, affecting not only immunity but gut microbiota and epithelial barrier integrity. While increased lymphangiogenesis is primarily associated with a good prognosis of IBD, increased lymphangiectasia, lymphadenopathy, and lymphatic vessel occlusion correlate with poor prognosis. IBD therapies that target the lymphatic system seek to increase lymphangiogenesis via induction of lymphangiogenic factors and inhibition of its antagonists. The resultant increased lymphatic flow coupled with other anti-inflammatory activities restores gut homeostasis.

Novel mechanisms and clinical trial endpoints in intestinal fibrosis

The incidence of inflammatory bowel diseases (IBD) worldwide has resulted in a global public health challenge. Intestinal fibrosis leading to stricture formation and bowel obstruction is a frequent complication in Crohn's disease (CD), and the lack of anti-fibrotic therapies makes elucidation of fibrosis mechanisms a priority. Progress has shown that mesenchymal cells, cytokines, microbial products, and mesenteric adipocytes are jointly implicated in the pathogenesis of intestinal fibrosis. This recent information puts prevention or reversal of intestinal strictures within reach through innovative therapies validated by reliable clinical trial endpoints. Here, we review the role of immune and non-immune components of the pathogenesis of intestinal fibrosis, including new cell clusters, cytokine networks, host-microbiome interactions, creeping fat, and their translation for endpoint development in anti-fibrotic clinical trials.

Role of Adipose Tissue in Inflammatory Bowel Disease

Inflammatory bowel diseases (IBDs), chronic inflammatory disorders affecting the gastrointestinal tract, include Crohn's disease and ulcerative colitis. There are increasing clinical and experimental data showing that obesity, especially visceral adiposity, plays a substantial role in the pathogenesis of IBD. Obesity seems to be an important risk factor also for IBD disease severity and clinical outcomes. Visceral adipose tissue is an active multifunctional metabolic organ involved in lipid storage and immunological and endocrine activity. Bowel inflammation penetrates the surrounding adipose tissue along the mesentery. Mesenteric fat serves as a barrier to inflammation and controls immune responses to the translocation of gut bacteria. At the same time, mesenteric adipose tissue may be the principal source of cytokines and adipokines responsible for inflammatory processes associated with IBD. This review is particularly focusing on the potential role of adipokines in IBD pathogenesis and their possible use as promising therapeutic targets.

Adipokine-Modulated Immunological Homeostasis Shapes the Pathophysiology of Inflammatory Bowel Disease

Inflammatory colon diseases, which are a global health concern, include a variety of gastrointestinal tract disorders, such as inflammatory bowel disease and colon cancer. The pathogenesis of these colon disorders involves immune alterations with the pronounced infiltration of innate and adaptive immune cells into the intestines and the augmented expression of mucosal pro-inflammatory cytokines stimulated by commensal microbiota. Epidemiological studies during the past half century have shown that the proportion of obese people in a population is associated with the incidence and pathogenesis of gastrointestinal tract disorders. The advancement of understanding of the immunological basis of colon disease has shown that adipocyte-derived biologically active substances (adipokines) modulate the role of innate and adaptive immune cells in the progress of intestinal inflammation. The biomedical significance in immunological homeostasis of adipokines, including adiponectin, leptin, apelin and resistin, is clear. In this review, we highlight the existing literature on the effect and contribution of adipokines to the regulation of immunological homeostasis in inflammatory colon diseases and discuss their crucial roles in disease etiology and pathogenesis, as well as the implications of these results for new therapies in these disorders.

Pathophysiology of Crohn's disease inflammation and recurrence

Chron’s Disease is a chronic inflammatory intestinal disease, first described at the beginning of the last century. The disease is characterized by the alternation of periods of flares and remissions influenced by a complex pathogenesis in which inflammation plays a key role. Crohn’s disease evolution is mediated by a complex alteration of the inflammatory response which is characterized by alterations of the innate immunity of the intestinal mucosa barrier together with a remodeling of the extracellular matrix through the expression of metalloproteins and increased adhesion molecules expression, such as MAcCAM-1. This reshaped microenvironment enhances leucocytes migration in the sites of inflammation, promoting a T_H1 response, through the production of cytokines such as IL-12 and TNF-α. IL-12 itself and IL-23 have been targeted for the medical treatment of CD. Giving the limited success of medical therapies, the treatment of the disease is invariably surgical. This review will highlight the role of inflammation in CD and describe the surgical approaches for the prevention of the almost inevitable recurrence.

Metabolic Regulation of Group 3 Innate Lymphoid Cells and Their Role in Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is characterized by chronic and relapsing inflammatory disorder of the intestine. IBD is associated with complex pathogenesis, and considerable data suggest that innate lymphoid cells contribute to the development and progression of the condition. Group 3 innate lymphoid cells (ILC3s) not only play a protective role in maintaining intestinal homeostasis and gut barrier function, but also a pathogenic role in intestinal inflammation. ILC3s can sense environmental and host-derived signals and combine these cues to modulate cell expansion, migration and function, and transmit information to the broader immune system. Herein, we review current knowledge of how ILC3s can be regulated by dietary nutrients, microbiota and their metabolites, as well as other metabolites. In addition, we describe the phenotypic and functional alterations of ILC3s in IBD and discuss the therapeutic potential of ILC3s in the treatment of IBD.

Ectopic Lymphoid Organs and Immune-Mediated Diseases: Molecular Basis for Pharmacological Approaches

Chronic inflammation is the result a persistent increase in the expression of several proinflammatory pathways with impaired inflammatory resolution. Ectopic lymphoid organs (ELOs), untypical lymphoid annexes, emerge during chronic inflammation and contribute to the physiopathology of chronic inflammatory disorders. This review discusses the pathophysiological role of ELOs in the progression of immune-mediated inflammatory diseases (IMIDs), including multiple sclerosis (MS), rheumatoid arthritis (RA), inflammatory bowel disease (IBD), atherosclerosis, and Sjögren syndrome (SSj). The molecular pathways underlying the emergence of ELOs are of interest for the development of novel pharmacological approaches for the management of chronic inflammatory diseases.

Strictureplasty versus bowel resection for the surgical management of fibrostenotic Crohn's disease: a systematic review and meta-analysis

BACKGROUND

Strictureplasty (SPX) conserves bowel length and minimizes the risk of developing short bowel syndrome in patients undergoing surgery for Crohn's disease (CD). However, SPX may be associated with a higher risk of recurrence compared with bowel resection (BR).

AIM

We sought to compare morbidity and recurrence following SPX and BR in patients with fibrostenotic CD.

METHODS

A systematic review was performed according to PRISMA and MOOSE guidelines. Observational studies that compared outcomes of CD patients undergoing either SPX or BR were identified. Log hazard ratios (InHR) for recurrence-free survival (RFS) and their standard errors were calculated from Kaplan-Meier plots or Cox regression models and pooled using the inverse variance method. Dichotomous variables were pooled as odds ratios (OR) using the Mantel-Haenszel method. Continuous variables were pooled as weighted mean differences.

RESULTS

Twelve studies of 1026 CD patients (SPX n = 444, 43.27%; BR with or without SPX n = 582, 56.72%) were eligible for inclusion. There was an increased likelihood of disease recurrence with SPX than with BR (OR 1.61; 95% CI, 1.03, 2.52; p = 0.04; I² = 0%). Patients who had a SPX alone had a significantly reduced RFS than those who underwent BR (HR 1.47; 95% CI, 1.08, 2.01; p = 0.02; I² = 0%). There was no difference in morbidity between the groups (OR 0.58; 95% CI, 0.26, 1.28; p = 0.18; I² = 0%).

CONCLUSION

SPX should only be performed in those patients with Crohn's strictures that are at high risk for short bowel syndrome and intestinal failure; otherwise, BR is the favored surgical technique for the management of fibrostenotic CD.

Meta-analysis of early bowel resection versus initial medical therapy in patient's with ileocolonic Crohn's disease

BACKGROUND

Early bowel resection (EBR) in ileocolonic Crohn's disease (CD) may be associated with more durable remission compared with initial medical therapy (IMT) even when biologic therapy is included.

AIM

To compare the efficacy of EBR versus IMT for ileocolonic CD METHODS: A systematic search was performed to identify studies that compared EBR (performed < 1 year from initial diagnosis) or IMT for the management of ileocolonic CD. Log hazard ratios (InHR) for relapse-free survival (RFS) and their standard errors were calculated from Kaplan-Meier plots and pooled using the inverse-variance method. Dichotomous variables were pooled as odds ratios (OR). Quality assessment of the included studies was performed using the Newcastle-Ottawa (NOS) and Jadad scales.

RESULTS

A total of 7 studies with 1863 CD patients (EBR n = 581, 31.2%; IMT n = 1282, 68.8%) were eligible for inclusion. There was a moderate-to-high risk of bias. The median NOS was 8 (range 7-9). There was a reduced likelihood of overall (OR, 0.53; 95% confidence interval (95% CI), 0.34, 0.83; p = 0.005) and surgical (OR, 0.47; 95% CI, 0.24, 0.91; p = 0.03) relapse with EBR. There was also a less requirement for maintenance biologic therapy (OR, 0.24; 95% CI, 0.14, 0.42; p < 0.0001). Patients who underwent EBR had a significantly improved RFS than those who underwent IMT (HR, 0.62; 95% CI, 0.52, 0.73; p < 0.001). There was no difference in morbidity (OR, 1.67; 95% CI, 0.44, 6.36; p = 0.45) between the groups.

CONCLUSION

EBR may be associated with less relapse and need for maintenance biologic therapy than IMT. 'Upfront' or early resection may represent a reasonable and cost-effective alternative to biologic therapy, especially in biologic-resistant subpopulations.

Chronic Inflammation: A Common Promoter in Tertiary Lymphoid Organ Neogenesis

Tertiary lymphoid organs (TLOs) frequently develop locally in adults in response to non-resolving inflammation. Chronic inflammation leads to the differentiation of stromal fibroblast cells toward lymphoid tissue organizer-like cells, which interact with lymphotoxin α1β2+ immune cells. The interaction initiates lymphoid neogenesis by recruiting immune cells to the site of inflammation and ultimately leads to the formation of TLOs. Mature TLOs harbor a segregated T-cell zone, B-cell follicles with an activated germinal center, follicular dendritic cells, and high endothelial venules, which architecturally resemble those in secondary lymphoid organs. Since CXCL13 and LTα₁β₂ play key roles in TLO neogenesis, they might constitute potential biomarkers of TLO activity. The well-developed TLOs actively regulate local immune responses and influence disease progression, and they are thereby regarded as the powerhouses of local immunity. In this review, we recapitulated the determinants for TLOs development, with great emphasis on the fundamental role of chronic inflammation and tissue-resident stromal cells for TLO neogenesis, hence offering guidance for therapeutic interventions in TLO-associated diseases.