MAIT cell activation and recruitment in inflammation and tissue damage in acute appendicitis.

Mucosal-associated invariant T (MAIT) cells are antimicrobial T cells abundant in the gut, but mechanisms for their migration into tissues during inflammation are poorly understood. Here, we used acute pediatric appendicitis (APA), a model of acute intestinal inflammation, to examine these migration mechanisms. MAIT cells were lower in numbers in circulation of patients with APA but were enriched in the inflamed appendix with increased production of proinflammatory cytokines. Using the patient-derived appendix organoid (PDAO) model, we found that circulating MAIT cells treated with inflammatory cytokines elevated in APA up-regulated chemokine receptors, including CCR1, CCR3, and CCR4. They exhibited enhanced infiltration of Escherichia coli-pulsed PDAO in a CCR1-, CCR2-, and CCR4-dependent manner. Close interactions of MAIT cells with infected organoids led to the PDAO structural destruction and death. These findings reveal a previously unidentified mechanism of MAIT cell tissue homing, their participation in tissue damage in APA, and their intricate relationship with mucosal tissues during acute intestinal inflammation in humans.

Increased IgE Deposition in Appendicular Tissue Specimens Is Compatible with a Type I Hypersensitivity Reaction in Acute Appendicitis.

BACKGROUND: IgE mediates type I hypersensitivity reaction and can be found in the mucosa of organs affected by allergy. Acute appendicitis (AA) is a common disease, but its etiology remains poorly understood. Here, we investigated IgE deposition in histological sections of AA samples to test the hypothesis that an allergic reaction may substantially contribute to the pathophysiology of AA. MATERIALS AND METHODS: In a retrospective study, we assessed the presence of IgE in appendicular specimens of histologically confirmed appendicitis and in the control group, comprised of negative appendicitis and incidental appendectomies, using a monoclonal antibody against human IgE. Samples from 134 appendectomies were included: 38 phlegmonous and 27 gangrenous appendicitis from the study group and 52 incidental appendectomies and 17 negative appendicitis from the control group. The slides were visualized by light microscopy, and a standard procedure was used to manually count the positive IgE staining cells. RESULTS: IgE staining was present in the cells of all but 5 appendicular specimens. We found a significantly increased number of IgE-positive cells in phlegmonous AA (median = 28) when compared to incidental appendectomy (median = 17) (p = 0.005; p < 0.0001 when adjusted for age and gender). No difference was found for gangrenous appendicitis. Discussion. The presence of IgE supports the contribution of an allergic reaction for the pathophysiology of phlegmonous appendicitis. The reduced number of IgE staining cells in gangrenous appendicitis can be due to tissue destruction, or, as been claimed by others, gangrenous appendicitis is a distinct entity, with different etiology. CONCLUSION: In this study, phlegmonous appendicitis had the highest number of IgE-positive appendicular cells. These findings suggest that an allergic reaction can contribute to the pathophysiology of AA, opening a novel possibility for preventive measures in a disease that typically requires surgery.

Acute appendicitis is associated with appendiceal microbiome changes including elevated Campylobacter jejuni levels.

OBJECTIVES: To compare the appendiceal microbiomes and examine the prevalence of Campylobacter species in the appendices of adult subjects with confirmed acute non-perforated appendicitis and controls with healthy appendices. DESIGN: Archived samples of formalin-fixed paraffin-embedded appendiceal tissues were obtained from 50 consecutive female subjects who underwent appendectomy for acute, non-perforated appendicitis, and 35 consecutive female controls who underwent incidental appendectomy during gynaecological surgery. RESULTS: 16S rRNA gene sequencing revealed that the relative abundances (RAs) of the major phyla in appendiceal tissues (Firmicutes, Proteobacteria, Bacteroidetes, and Actinobacteria) were similar in both groups. Beta diversity was significantly different due to differences in Bacteroidetes and Proteobacteria (p<0.0001). Within Proteobacteria, RAs of classes Alphaproteobacteria (~21%, fold change (FC)=1.31, false discovery rate (FDR) p value=0.03) and Epsilonproteobacteria (~1%, FC=0.25, FDR p value>0.05) were increased in acute appendicitis samples. RAs of unknown genera from families Burkholderiaceae and Enterobacteriaceae were decreased in appendicitis samples, and 14 genera were increased, including Neisseria, Acinetobacter and Campylobacter. Quantitative PCR revealed that levels of Campylobacter jejuni DNA, but not other Campylobacter species or pathogens tested, were significantly higher in appendicitis samples than in controls (p=0.013). Using a cut-off of 0.31 pg/µL, 40% of appendicitis cases and 6% of controls were positive for C. jejuni, indicating specificity of 93.7% (95% Cl 79.2 to 99.2), sensitivity of 40.9% (95% Cl 24.7 to 54.5), and OR of 10.38 (Fisher's p value=0.0006, 95% Cl 2.3 to 47.4). CONCLUSIONS: Our findings indicate that Campylobacter jejuni may be a significant cause of acute appendicitis. This supports earlier studies and suggests that targeted antibiotic therapies could be an alternative treatment for a subset of non-complicated acute appendicitis cases.

Appendix Tumor Microenvironment.

The pathological features of the appendix tumors fundamentally recall those of the more frequent colorectal neoplasms, although with a higher relative incidence of carcinoids, due to the abundant presence of enteroendocrine cells in the appendix wall. Moreover, different types of lymphomas, Hodgkin and non-Hodgkin, arising from the extra-nodal mucosal-associated lymphatic tissue, can be encountered. The appendix tumor microenvironment (TME) consists of a cellular component and of a noncellular component: the former includes the immunocompetent cells, while the latter represents the support stroma. Particularly in carcinoids, the immune cell reaction can be explicated by tumor-infiltrating lymphocytes, which, in some circumstances, may arrange around and inside the tumor in a brisk fashion influencing favorably the prognosis. This active reaction has to be distinguished from any preexisting inflammatory condition of the appendix and from superimposed tumor complications, such as infection or ischemia. In practice, we consider the appendix TME a complex framework with immunological, mechanic, and metabolic functions, all supported by a marked neo-lymphoangiogenesis.

Factors Involved in the Degeneration of Lymphoid Tissue in the Appendix.

INTRODUCTION: Studies evaluating the age-related alteration of human appendix have been reported. Although the appendix shows a degeneration of lymphoid tissues with aging, the mechanism of action remains unclear. MATERIAL AND METHODS: Surgically resected appendix tissues from patients with colon cancer, intestinal malrotation and ulcerative colitis (UC) were utilized for histological and flow cytometric analysis. RESULTS: Histological analysis showed that aging may induce steatotic changes in the appendix. However, there was no clear association between appendiceal fibrosis and aging. Lymphoid follicles in the appendix may start to develop before 5 days of age, gradually mature, and eventually disappear with aging. Flow cytometric analysis clearly identified a lymphocyte population in the appendix at 5 days, 45 and 75 years of age, and lymphoid follicles were also confirmed histologically. In contrast, lymphoid population was rarely detectable in the appendix at 79 and 80 years of age, and no lymphoid follicles were present histologically. Interestingly, cytograms from a case at 5 days of age suggested the existence of immature immune cells, as forward scatter showed an increase in cell size of the lymphocyte population. Histological analysis in UC patients found submucosal fat in the appendix of a case 66 years of age. Lymphoid follicular formation and mucosal structure were disrupted in cases of 70 and 72 years of age. UC patients may be more susceptible to steatotic change. Cytograms from appendices of UC patients also supported these histological findings. Our study confirms previous results that lymphoid tissues in the appendix degenerate over time, and proposes that inflammatory insult may facilitate the degenerative process in patients with UC.

The Appendix in Parkinson's Disease: From Vestigial Remnant to Vital Organ?

Parkinson's disease (PD) has long been considered a brain disease, but studies now point to the gastrointestinal (GI) tract as a potential starting point for PD. In particular, the human vermiform appendix has been implicated in PD. The appendix is a tissue rich in immune cells, serving as part of the gut-associated lymphoid tissue and as a storehouse for the gut microbiome. The functions of the appendix converge with recent evidence demonstrating that gut inflammation and shifts in the microbiome are linked to PD. Some epidemiological studies have linked removal of the appendix to lowered PD risk, though there is controversy among these associations. What is apparent is that there is an abundance of aggregated forms of α-synuclein in the appendix relevant to PD pathology. α-Synuclein pathology is thought to propagate from gut to brain via the vagus nerve, which innervates GI tract locations, including the appendix. Remarkably, α-synuclein aggregates in the appendix occur not only in PD patients, but are also present in healthy individuals. This has led to the proposal that in the appendix α-synuclein aggregates are not unique to PD. Moreover, the molecular events leading to PD and the mechanisms by which α-synuclein aggregates transfers from gut to brain may be identifiable in the human appendix. The influence of the appendix on GI inflammation, autoimmunity, microbiome storage, and the lymphatic system may be yet unexplored mechanisms by which the appendix contributes to PD. Overall, the appendix represents a promising tissue site to advance our understanding of PD pathobiology.

The vermiform appendix: an immunological organ sustaining a microbiome inoculum.

The hominoid vermiform appendix has been characterized as a diverticulum of the caecum and describes an entity at the juxtaposition of the colon in the confluence of tanias. The independent development of the lymphoid follicle centres of the appendix is progressed at birth in the presence of the intestinal commensal microbiome, an obligatory prompt for the diversification of intestinal and extra-intestinal mucosal immunological tissue. In the vermiform appendix, this activity is centred on further developing the inventory of primary antibodies and the maturation of T- and B-lymphocyte cells in the follicles within the lymphoid tissue. Furthermore, the columnar epithelia, enterocytes and goblet cells comprise the complement of cells that occupy the lamina propria and muscularis mucosae of the vermiform appendix's mucosa, while macrophages and an abundance of immunoglobulin A and immunoglobulin G generating plasma cells seed the lamina propria Intraepithelial immune cells consisting predominantly of specific CD8+ T regulatory lymphocytes occupy sites in the appendix analogous to those present in the intestinal epithelia of the caecal colon. The complement of bacterial genera concealed in the vermiform appendix is posited extant as a biofilm inoculum of the intestinal commensal microbiome. This facilitates re-inoculation of the proximal colon and to a lesser degree the terminal ilium post an intestinal perturbation such as occurs with daily lifestyle stressors, dietary choices and the short-term administration of antibiotics rather than an infectious fulminant colitis. A plausible appreciation results of the importance of multiple immunological aspects of a healthy vermiform appendix and the provision of a commensal biofilm to the gut that repairs a dysbiotic microbiome contributing to balancing intestinal pro- and anti-inflammatory activity for maintaining homeostasis in the gut. Since the composition of the gut microbiome can vary over the short-term and long-term, it is plausible that the appendix inoculum may be instrumental in maintaining the intestinal microbiome.

Acute eosinophilic appendicitis simulating uncomplicated appendicitis.

Acute appendicitis is one of the most common abdominal emergencies worldwide. Uncomplicated appendicitis (UA), which does not involve perforation or peritonitis, has recently been treated with antibiotic therapy. Here, we report a case of acute eosinophilic appendicitis (AEA) that simulated UA and did not respond to antibiotic therapy. A 20-year-old Japanese woman emergently presented with the chief complaint of pain at the right iliac fossa. CT showed only swelling of the appendix. She was diagnosed with UA, and she received antibiotic therapy initially. However, the treatment was not effective and appendectomy was performed. The final histopathological diagnosis was AEA. The findings of this case suggest that AEA is likely to be diagnosed as UA. As AEA can simulate UA, the possibility of AEA should be considered when antibiotic therapy is not effective.

The immunological functions of the Appendix: An example of redundancy?

Biological redundancy ensures robustness in living organisms at several levels, from genes to organs. In this review, we explore the concept of redundancy and robustness through an analysis of the caecal appendix, an organ that is often considered to be a redundant remnant of evolution. However, phylogenic data show that the Appendix was selected during evolution and is unlikely to disappear once it appeared. In humans, it is highly conserved and malformations are extremely rare, suggesting a role for that structure. The Appendix could perform a dual role. First, it is a concentrate of lymphoid tissue resembling Peyer's patches and is the primary site for immunoglobulin A production which is crucial to regulate the density and quality of the intestinal flora. Second, given its shape and position, the Appendix could be a unique niche for commensal bacteria in the body. It is extremely rich in biofilms that continuously shed bacteria into the intestinal lumen. The Appendix contains a microbiota as diverse as that found in the colon and could replenish the large intestine with healthy flora after a diarrhea episode. In conditions of modern medicine hygiene, and people live healthy without their appendix. However, several reports suggest that the effects of appendectomy could be subtler and associated with the development of inflammatory conditions such as inflammatory bowel disease (IBD), heart disease but also in less expected disorders such as Parkinson's disease. Lack of an Appendix also predicts a worsen outcome for recurrent Clostridium difficile infection, which is the first nosocomial infection in hospitals. Here, we review the literature and in combination with our own data, we suggest that the Appendix might be redundant in its immunological function but unique as a reservoir of microbiota.

B cell activation in the cecal patches during the development of an experimental colitis model.

Although previous studies have suggested that appendix seems to be involved in the colitis, the role of this in the pathogenesis remains unclear. In this study, we assessed the importance of appendiceal lymphoid follicles, specifically the cecal patches (CP) in mice, using an experimental colitis model. Treatment with oxazolone resulted in ulcerations particularly at CP with follicular expansion as well as colitis. The colitis was attenuated by either appendectomy or the absence of mature B cells. We therefore established an intravital imaging system accompanied by the fluorescence resonance energy transfer technology to analyze the dynamic immune response of CP B cells. Our observation revealed frequent Ca2+ signaling in CP B cells during the early phase of colitis development. These findings suggested that the CP B cells may be involved in the pathogenesis of colitis including inflammatory bowel diseases in humans.

Composition of the cellular infiltrate in patients with simple and complex appendicitis.

BACKGROUND: It is now well established that there are two types of appendicitis: simple (nonperforating) and complex (perforating). This study evaluates differences in the composition of the immune cellular infiltrate in children with simple and complex appendicitis. MATERIALS AND METHODS: A total of 47 consecutive children undergoing appendectomy for acute appendicitis between January 2011 and December 2012 were included. Intraoperative criteria were used to identify patients with either simple or complex appendicitis and were confirmed histopathologically. Immune histochemical techniques were used to identify immune cell markers in the appendiceal specimens. Digital imaging analysis was performed using Image J. RESULTS: In the specimens of patients with complex appendicitis, significantly more myeloperoxidase positive cells (neutrophils) (8.7% versus 1.2%, P < 0.001) were detected compared to patients with a simple appendicitis. In contrast, fewer CD8+ T cells (0.4% versus 1.3%, P = 0.016), CD20 + cells (2.9% versus 9.0%, P = 0.027), and CD21 + cells (0.2% versus 0.6%, P = 0.028) were present in tissue from patients with complex compared to simple appendicitis. CONCLUSIONS: The increase in proinflammatory innate cells and decrease of adaptive cells in patients with complex appendicitis suggest potential aggravating processes in complex appendicitis. Further research into the underlying mechanisms may identify novel biomarkers to be able to differentiate simple and complex appendicitis.

Appendectomy, tonsillectomy, and risk for sarcoidosis - A hospital-based case-control study in Japan.

BACKGROUND: The role of surgery in the onset of sarcoidosis is unclear. We investigated whether surgery is an internal environmental factor for sarcoidosis onset within the Japanese population. METHODS: We enrolled 222 patients diagnosed with sarcoidosis (78 men, 144 women) who were admitted to our department between 1984 and 2012. We also enrolled 529 control subjects (251 men, 278 women), who were matched for sex, age at admission, and year of admission. Surgical history, family history, and smoking status were evaluated. RESULTS: Multivariate analysis correlated history of appendectomy (OR, 1.55; 95% CI, 1.05-2.29) and tonsillectomy (OR, 2.79; 95% CI, 0.91-8.56) with the occurrence of sarcoidosis; other surgical procedures had no correlation. In women, appendectomy had a stronger association with sarcoidosis (OR, 1.69; 95% CI, 1.05-2.73), as opposed to that in men (OR, 1.39; 95% CI, 0.68-2.85). This association was greater in women aged ≥45 years than in those aged <45 years. There was a stronger correlation between tonsillectomy and sarcoidosis in women (OR, 3.30; 95% CI, 0.88-12.39), than in men (OR, 1.26; 95% CI, 0.10-16.52). ORs for sarcoidosis were 5.55 (95% CI, 2.02-15.27) and 0.97 (95% CI, 0.52-1.84) in women aged ≥45 years with a history of appendectomy at <20 years and ≥20 years, respectively, with the former being statistically significant. CONCLUSIONS: Appendix and tonsil removal was associated with sarcoidosis onset, suggesting their potential protective role against sarcoidosis development. Further studies are needed to minimize possible confounding factors.

The immunology of the vermiform appendix: a review of the literature.

This literature review assesses the current knowledge about the immunological aspects of the vermiform appendix in health and disease. An essential part of its immunological function is the interaction with the intestinal bacteria, a trait shown to be preserved during its evolution. The existence of the appendiceal biofilm in particular has proved to have a beneficial effect for the entire gut. In assessing the influence of acute appendicitis and the importance of a normally functioning gut flora, however, multiple immunological aspects point towards the appendix as a priming site for ulcerative colitis. Describing the immunological and microbiotical changes in the appendix during acute and chronic inflammation of the appendix, this review suggests that this association becomes increasingly plausible. Sustained by the distinct composition of cells, molecules and microbiota, as well as by the ever more likely negative correlation between the appendix and ulcerative colitis, the idea of the appendix being a vestigial organ should therefore be discarded.

[DYNAMICS OF INDICES OF A LOCAL IMMUNITY IN AN ACUTE APPENDICITIS].

Abstract The results of investigation on dynamics of a local immunity indices in an acute appendicitis, depending on the pathological process stage as well as on bacteriological investigation of parietal microflora of processus vermicularis, were adduced. The sIgA and lisocymal dynamics have witnessed that while a destructive process progressing their concentration was enhanced, and in a gangrenous acute appendicitis they practically disappeared. Due to affection of a barrier function of the processus vermicularis wall a favorable conditions were created for the microorganisms intramural translocation as well as to abdominal cavity.

Intestinal stem cells and intestinal homeostasis in health and in inflammation: A review.

BACKGROUND: The human intestine is a complex group of organs, highly specialized in processing food and providing nutrients to the body. It is under constant threat from microbials and toxins and has therefore developed a number of protective mechanisms. One important mechanism is the constant shedding of epithelial cells into the lumen; another is the production and maintenance of a double-layered mucous boundary in which there is continuous sampling of the luminal microbiota and a persistent presence of antimicrobial enzymes. However, the gut needs commensal bacteria to effectively break down food into absorbable nutrients, which necessitates constant communication between the luminal bacteria and the intestinal immune cells in homeostasis. Disruption of homeostasis, for whatever reason, will give rise to (chronic) inflammation. DISCUSSION: Both medical and surgical management of this disruption is discussed.

Appendiceal Immunoglobulin G4-Related Disease Mimicking Appendiceal Tumor or Appendicitis: A Case Report.

Immunoglobulin G4 (IgG4)-related disease is an autoimmune disease that forms tumorous lesions. Several cases involving various organs are reported, however, IgG4-related disease involving appendix has not been reported yet. In this report, we presented a case of IgG4-related disease of appendix, which raised a suspicion of appendiceal tumor or usual appendicitis and, therefore, led to unnecessary surgical resection. IgG4-related disease should be considered in the differential diagnosis for a mass-like swelling of the appendix, in order to avoid unnecessary surgery.

The Link between the Appendix and Ulcerative Colitis: Clinical Relevance and Potential Immunological Mechanisms.

The human appendix has long been considered as a vestigial organ, an organ that has lost its function during evolution. In recent years, however, reports have emerged that link the appendix to numerous immunological functions in humans. Evidence has been presented for an important role of the appendix in maintaining intestinal health. This theory suggests that the appendix may be a reservoir or 'safe house' from which the commensal gut flora can rapidly be reestablished if it is eradicated from the colon. However, the appendix may also have a role in the development of inflammatory bowel disease (IBD). Several large epidemiological cohort studies have demonstrated the preventive effect of appendectomy on the development of ulcerative colitis, a finding that has been confirmed in murine colitis models. In addition, current studies are examining the possible therapeutic effect of an appendectomy to modulate disease course in patients with ulcerative colitis. This literature review assesses the current knowledge about the clinical and immunological aspects of the vermiform appendix in IBD and suggests that the idea of the appendix as a vestigial remnant should be discarded.

Role of Eosinophils in Acute Appendicitis.

INTRODUCTION: High negative appendectomy rate still prevails on conventional histologic examination. Increased mural eosinophilic infiltrate had been observed in acute appendicitis. Present study aimed to evaluate the role of mural eosinophils in clinically suspected acute appendicitis but histological normal appendix, as an indicator of acute inflammation, alone or in association with edema and to estimate the cut off value for high eosinophil count for the diagnosis of acute appendicitis. METHODS: A prospective cross sectional study was conducted on appendectomy specimens which were categorized into three groups of classical acute appendicitis, negative appendectomy and control. HandE and Giemsa stained section were studied for the presence of mural eosinophilic infiltrate, mast cells and edema. RESULTS: Of total 170 cases, group 1 comprised of 68 cases, group 2 consisted of 78 cases and group 3 consisted of 24 cases. Mean eosinophil and mast cell counts in the muscularis propria were significantly higher in CAA and NA categories when compared to control group. Positive association was found between high eosinophil count and edema in CAA and NA categories. Cut off value of ≥6/ mm2 for mural eosinophil count was not significantly different in between NA and control categories. CONCLUSIONS: Increased mural eosinophils were significantly present in acute appendicitis and clinically suspected acute appendicitis but histological normal appendix when compared with control group. Sole presence of increased mural eosinophils might represent acute inflammation. However, cut off value for high eosinophil count could not be established to suggest acute appendicitis.

Chemokine-mediated B cell trafficking during early rabbit GALT development.

Microbial and host cell interactions stimulate rabbit B cells to diversify the primary Ab repertoire in GALT. B cells at the base of appendix follicles begin proliferating and diversifying their V-(D)-J genes around 1 wk of age, ∼5 d after B cells first begin entering appendix follicles. To gain insight into the microbial and host cell interactions that stimulate B cells to diversify the primary Ab repertoire, we analyzed B cell trafficking within follicles during the first week of life. We visualized B cells, as well as chemokines that mediate B cell homing in lymphoid tissues, by in situ hybridization, and we examined B cell chemokine receptor expression by flow cytometry. We found that B cells were activated and began downregulating their BCRs well before a detectable B cell proliferative region appeared at the follicle base. The proliferative region was similar to germinal center dark zones, in that it exhibited elevated CXCL12 mRNA expression, and B cells that upregulated CXCR4 mRNA in response to signals acquired from selected intestinal commensals localized in this region. Our results suggest that after entering appendix follicles, B cells home sequentially to the follicle-associated epithelium, the follicular dendritic cell network, the B cell/T cell boundary, and, ultimately, the base of the follicle, where they enter a proliferative program and diversify the primary Ab repertoire.