Human Peyer's patches: lympho-epithelial relationships and characteristics of immunoglobulin-producing cells

Villous B cells of the small intestine are specialized for invariant NK T cell dependence

B cells are important in mucosal microbial homeostasis through their well-known role in secretory IgA production and their emerging role in mucosal immunoregulation. Several specialized intraintestinal B cell compartments have been characterized, but the nature of conventional B cells in the lamina propria is poorly understood. In this study, we identify a B cell population predominantly composed of surface IgM(+) IgD(+) cells residing in villi of the small intestine and superficial lamina propria of the large intestine, but distinct from the intraepithelial compartment or organized intestinal lymphoid structures. Small intestinal (villous) B cells are diminished in genotypes that alter the strength of BCR signaling (Bruton tyrosine kinase(xid), Galphai2(-/-)), and in mice lacking cognate BCR specificity. They are not dependent on enteric microbial sensing, because they are abundant in mice that are germfree or genetically deficient in TLR signaling. However, villous B cells are reduced in the absence of invariant NK T cells (Jalpha18(-/-) or CD1d(-/-) mice). These findings define a distinct population of conventional B cells in small intestinal villi, and suggest an immunologic link between CD1-restricted invariant NK T cells and this B cell population.

Intestinal M cells: The fallible sentinels?

The gastrointestinal tract represents the largest mucosal membrane surface in the human body. The immune system in the gut is the first line of host defense against mucosal microbial pathogens and it plays a crucial role in maintaining mucosal homeostasis. Membranous or microfold cells, commonly referred to as microfold cells, are specialized epithelial cells of the gut-associated lymphoid tissues (GALT) and they play a sentinel role for the intestinal immune system by delivering luminal antigens through the follicle-associated epithelium to the underlying immune cells. M cells sample and uptake antigens at their apical membrane, encase them in vesicles to transport them to the basolateral membrane of M cells, and from there deliver antigens to the nearby lymphocytes. On the flip side, some intestinal pathogens exploit M cells as their portal of entry to invade the host and cause infections. In this article, we briefly review our current knowledge on the morphology, development, and function of M cells, with an emphasis on their dual role in the pathogenesis of gut infection and in the development of host mucosal immunity.

Keynote review: Intestinal Peyer's patch M cells and oral vaccine targeting

Specialized M cells in the follicle-associated epithelium of intestinal Peyer's patches serve as portals for diverse particulates. Following antigen handover to dome lymphocytes, a protective mucosal antibody secretion ensues. One approach to oral vaccine delivery is to mimic the entry pathways of pathogens via M cells. The paucity of human tissue for in vitro investigation has hampered the discovery of M-cell pathogen receptors; however an in vitro human M like-cell culture model displays many expected phenotypic features. Comparative studies using microarrays reveal several novel M-cell surface receptors that could be used to potentially target orally delivered antigens.

Selective adherence of IgA to murine Peyer's patch M cells: evidence for a novel IgA receptor

M cells represent the primary route by which mucosal Ags are transported across the intestinal epithelium and delivered to underlying gut-associated lymphoid tissues. In rodents and rabbits, Peyer's patch M cells selectively bind and endocytose secretory IgA (SIgA) Abs. Neither the nature of the M cell IgR nor the domains of SIgA involved in this interaction are known. Using a mouse ligated ileal loop assay, we found that monoclonal IgA Abs with or without secretory component, but not IgG or IgM Abs, bound to the apical surfaces of Peyer's patch M cells, indicating that the receptor is specific for the IgA isotype. Human serum IgA and colostral SIgA also bound to mouse M cells. The asialoglycoprotein receptor or other lectin-like receptors were not detected on the apical surfaces of M cells. We used recombinant human IgA1 and human IgA2 Abs and domain swapped IgA/IgG chimeras to determine that both domains Calpha1 and Calpha2 are required for IgA adherence to mouse Peyer's patch M cells. This distinguishes the M cell IgA receptor from CD89 (FcalphaI), which binds domains Calpha2-Calpha3. Finally, we observed by immunofluorescence microscopy that some M cells in the human ileum are coated with IgA. Together these data suggest that mouse, and possibly human, M cells express an IgA-specific receptor on their apical surfaces that mediates the transepithelial transport of SIgA from the intestinal lumen to underlying gut-associated organized lymphoid tissues.

Uncertainties - discrepancies in immunology

The many immunological observations and results from in-vitro or in-vivo experiments vary, and their interpretations differ enormously. A major problem is that within a normal distribution of biological phenomena, which are measurable with many methods, virtually anything is possible. Within a coevolutionary context, the definition of biologically relevant thresholds is an important key to improve our understanding of weaknesses and strengths of the immune system. This review is a personal view, comparing textbook rules and experiments using model antigens with observations on immunity against infections or tumors to critically evaluate our perception and understanding of specificity, affinity maturation, antigen presentation, selection of the class of the immune response, immunological memory and protective immunity, positive selection of T cells and self/nonself discrimination.

The immunology of inflammatory bowel disease

The dogma of systemic immunity can be ignored in relation to mucosal immunity. These distinct immune systems evolved based on specific environmental realities. Given the potentially hostile environment encountered by the mucosal immune system, it is a necessary adaptation that the overall tone is one of suppression. Breaches in this tone may lead to chronic inflammation. Understanding how specific components and processes of the mucosal immune system interact with the environment will elucidate the pathogenesis of IBD and lead to novel therapeutic approaches.

Vimentin, cytokeratin 8 and cytokeratin 18 are not specific markers for M-cells in human palatine tonsils

Standard immunohistochemical methods were used to detect the presence of vimentin, cytokeratin 8, cytokeratin 18, macrophages and Langerhans cells in the human tonsillar epithelium in formalin-fixed and frozen tissue specimens. Vimentin detection was restricted to infiltrating cells of the lymphoid series, dendritic and vascular endothelial cells. All epithelial cells were negative. Cytokeratin 8 and 18 were readily detected in a large proportion of epithelial cells lining the crypt, but these cells bore no resemblance to the intestinal M-cells. Langerhans cells and macrophages were seen in both the oropharyngeal and crypt epithelium and were more common in the latter. This study confirms the presence of antigen-presenting cells, macrophages and Langerhans cells in the tonsillar epithelium and shows that intermediate filament proteins, vimentin, cytokeratin 8 and 18 are unreliable markers for human tonsillar M-cells, if indeed such cells exist in human tonsils.

Ocular pANCA antigens are expressed in nonpigmented ciliary body epithelium and are conserved in multiple mammalian species

PURPOSE

pANCA marker autoantibody is expressed by a subset of patients with anterior uveitis. A recombinantly isolated pANCA monoclonal antibody, Fab 5-3, identifies ocular expression of corresponding pANCA antigens in human ciliary body and retina. In this study, Fab 5-3 was used to explore pANCA antigen expression in ocular tissues of multiple mammalian species and identify the ciliary body cell type expressing the pANCA antigen.

METHODS

Ocular tissues were obtained from several mammalian species and evaluated for expression of the pANCA (Fab 5-3) antigen(s) using immunohistochemistry and Western analysis of tissue extracts. Additionally, primary cultures of nonpigmented and pigmented rabbit ciliary body epithelium were analyzed for pANCA expression using immunofluorescence and Western analysis.

RESULTS

Ocular pANCA (Fab 5-3) antigen expression was observed by immunohistochemistry only in the cytoplasm of retinal ganglion cells and ciliary body epithelium. Retinal antigen expression was conserved in all species examined. Ciliary body expression was observed in human, rabbit, rat, and mouse, but not in pig or cow. Antigen expression in the rabbit ciliary body was restricted to the nonpigmented layer as defined in primary cultures of nonpigmented and pigmented ciliary body epithelium. Immunoreactive proteins in both the human and rabbit included a 32-33 kDa doublet (histone H1), and novel 80 and 100 kDa proteins.

CONCLUSIONS

This study identifies ocular pANCA antigen expression in multiple mammalian species localized to the retinal ganglion cell layer and the non-pigmented ciliary body epithelium. The present study also establishes novel 80 and 100 kDa proteins which may correspond to the cytoplasmic antigens detected in situ and can be further characterized biochemically and immunologically using small animal model systems.

Mucosal immunity and gastrointestinal antigen processing

The intestine is the largest lymphoid organ in the body by virtue of lymphocyte numbers and quantity of immunoglobulin produced. This is largely related to the enormous antigen load to which these cells are exposed on a daily basis. However, despite this, the mucosa-associated lymphoid tissue appears to be regulated by unique mechanisms, and this is reflected in specific phenomena (oral tolerance, controlled or physiologic inflammation) as well as unusual lymphoid populations (intraepithelial lymphocytes) that respond to alternative pathways of activation. This, coupled with the existence of novel antigen-presenting cells (intestinal epithelial cells) sets the scene for distinct immune responses. It is these distinct regulatory factors that support immunosuppression or tolerance rather than active immunity at a site juxtaposed to the external environment. This review defines these novel interactions and suggests how alteration in normal function may result in allergic or inflammatory responses. A clearer understanding of mucosal immunoregulation may lead to new therapeutic approaches for these diseases.

Mast cell and neuroendocrine cytoplasmic autoantigen(s) detected by monoclonal pANCA antibodies

pANCA is a marker antibody expressed in most patients with ulcerative colitis, and its cognate antigen is potentially an immunologic target in this disease. This study evaluates whether pANCA detects an autoantigen that is expressed in the colonic mucosa. Immunohistochemistry of colon specimens with human pANCA monoclonal antibodies (Fab 5-2 and 5-3) revealed a minor population of immunoreactive mucosal cells bearing a cytoplasmic vesicle antigen. By distribution, morphology, and tryptase expression, these were identified as mast cells. Immunofluorescent analysis revealed similar immunoreactivity of mouse mast cell lines and human KU812. Western analysis of mouse mast cell lines revealed immunoreactive proteins, and these were distinct from previously proposed pANCA antigens (histone H1, HMG 1 and 2, and neutrophil vesicle antigens). Cognate antigen for Fab 5-2 and 5-3 was also expressed in other tissue mast cells, cerebellar neurons, and pancreatic islet cells. These findings identify a novel cytoplasmic autoantigen(s) associated with UC by its presence in colonic mucosa and recognition by a disease-associated marker antibody.

Larynx-associated lymphoid tissue (LALT) in young children

BACKGROUND

Mucosa-associated lymphoid tissue (MALT) plays a central role in mucosal immunity. Whereas the characteristics and function of MALT in the intestine are well established, almost nothing is known about MALT in the larynx.

METHODS

In this study we examined the morphology and the lymphocyte subset composition of MALT in the larynges of children who had died of sudden infant death or various defined traumatic or nontraumatic causes.

RESULTS

Organized lymphoid tissue was found in the supraglottic parts of the larynx in nearly 80% of the children in both groups. This lymphoid tissue showed all morphological signs of MALT, such as typical lymphoid follicles with germinal centers, infiltration of the overlying epithelium by lymphocytes, and high endothelial venules (HEV). Thus we will use the term LALT (larynx-associated lymphoid tissue) to refer to this tissue. The lymphoid follicles of LALT contained mainly B lymphocytes with some CD4+ lymphocytes in the germinal centers. Remarkably, T lymphocytes of both subset types and B lymphocytes were observed in comparable numbers in the parafollicular area.

CONCLUSIONS

We assume that LALT is a physiological structure of the larynx in young children. The morphology and the distribution of lymphocyte subsets are similar to those of MALT in the human gut. LALT may be a regular part of the mucosal immune system in young children with the role of respiratory inductive site for mucosal immunity.

Nasal-associated lymphoid tissue is an inductive site for rat tear IgA antibody responses

The role of nasal-associated lymphoid tissue (NALT) as a mucosal inductive site for tear IgA antibody responses was investigated in the rat model. Fluorescent microspheres were shown to access and be taken up by NALT after intranasal of ocular-topical administration, although fewer microspheres were found in the latter case. Tear IgA anti-DNP antibody responses to dinitrophenylated Streptococcus pneumoniae were 6 micrograms/ml at day 7, 10 micrograms/ml at day 10, and were still detectable on day 21 (5 micrograms/ml) following ocular or gastrointestinal immunization. Intranasal immunization induced tear IgA responses which were 1.7-fold higher at day 7 (10 micrograms/ml), peaked by day 10 (14 micrograms/ml) and were still 1.6-fold higher (8 micrograms/ml) at day 21 than responses of ocular or gastrointestinal groups. These findings suggest that intranasal immunization may be more effective than ocular or gastrointestinal administration in eliciting tear IgA antibody responses and, taken together with the microsphere data, indicate that NALT can serve as an inductive site for ocular mucosal IgA responses.

Pathogenesis of aphthoid ulcers in Crohn's disease: correlative findings by magnifying colonoscopy, electron microscopy, and immunohistochemistry

BACKGROUND

The mechanism of ulceration in Crohn's disease remains unknown.

AIMS

To clarify the role of the follicle associated epithelium (FAE) of colonic lymphoid nodules in the formation of ulcers in Crohn's disease.

METHODS

After identification of colonic lymphoid nodules and aphthoid lesions by magnifying colonoscopy, 76 biopsy specimens were obtained from 10 patients with Crohn's disease and three patients with colonic lymphoid hyperplasia. This study correlated magnifying colonoscopic, electron microscopic, and immunohistochemical findings of biopsy specimens.

RESULTS

In Crohn's disease, scanning electron microscopy of lymphoid nodules surrounded by a red halo without visible erosions by magnifying colonoscopy, showed surface erosions 150-200 microns in size. These lymphoid nodules with red halos had small erosions either light microscopically or electron microscopically in 18 of 21 specimens (86%). Correlation of scanning and transmission electron microscopy showed residues of FAE including M cells at the edges of the erosions. In immunohistochemical studies, HLA-DR antigen was limited in M cells of FAE in the patients with lymphoid hyperplasia without inflammatory bowel disease. In Crohn's disease patients in remission, however, HLA-DR antigen was strongly expressed over the entire FAE of lymphoid nodules with a red halo endoscopically, while the expression was weak and irregular in the mucosa surrounding the lymphoid nodules. HLA-DR was strongly expressed in the entire inflamed colonic mucosa in the active stage.

CONCLUSION

The red halo appearance surrounding lymphoid follicles seems to precede visible aphthoid ulcers and suggests that ulcerations in Crohn's disease originate from FAE, possibly related to its physiological role as a portal of entry for potentially pathogenic agents.

Morphologic evaluation of the pathogenesis of bacterial enteric infections

Current advances in the understanding of the pathogenicity of the agents of diarrheal infections, Vibrio cholerae, diarrheagenic E. coli, Shigella, Salmonella, and enteropathogenic Yersinia, have, to a great extent, become possible due to morphological studies of host-pathogen interactions in natural and experimental infections. Despite a multigenic nature and a diversity of pathogenic features in the bacterial species and even in serogroups of the same species, it is now possible to delineate four major patterns of interaction of enteric pathogens with their cellular targets, the enterocytes, and with the immune apparatus of the gut. These patterns, epicellular cytotonic, epicellular restructuring cytotonic, invasive intraepithelial cytotonic and cytotoxic, and invasive transcellular cytotonic and cytotoxic bacteremic, underlie early pathogenesis and clinical manifestations in the respective diarrheal diseases. In this review, the results of the morphological analyses of these patterns over the last 3 decades as well as some methodological problems encountered in the interpretation of morphological observations are discussed.

Rat intestinal M cells contain acidic endosomal-lysosomal compartments and express class II major histocompatibility complex determinants

BACKGROUND

It is generally believed that M cells do not modify the antigens they transport from the intestinal lumen to underlying immunocompetent cells because it has been reported that M cells contain few elements of the lysosomal system.

METHODS

We used specific cytochemical and immunocytochemical probes to examine whether M cells in jejunal Peyer's patches of adult rats contain the requisite intracellular components to process and potentially present endocytosed antigens.

RESULTS

M cells contained acid phosphatase-enriched prelysosomelike and lysosomelike structures. A basic congener of dinitrophenol, which concentrates in acidic cell compartments, is localized following its instillation into Peyer's patch-containing ligated jejunal loops to the endosomal-lysosomal system of M cells. Prelysosomelike and lysosomelike structures in ultrathin cryosections of M cells reacted with polyclonal antibody to a membrane glycoprotein (lgp120) enriched in prelysosomes and lysosomes. Using monoclonal antibody OX6 as a probe, M cells expressed the major histocompatibility complex (MHC) class II determinant, Ia, on the basolateral plasma membrane and in organelles with structural features of endosomes, prelysosomes, and lysosomes. Expression was enhanced by pretreatment with interferon gamma.

CONCLUSIONS

M cells possess acidic endosomal and acid phosphatase-containing prelysosomal and lysosomal compartments and express MHC class II determinants. Hence, M cells may have the capacity to process and present endocytosed antigens to adjacent intraepithelial T lymphocytes.

HLA-DR expression on M cells overlying Peyer's patches is a common feature of human small intestine

The expression of major histocompatibility complex (MHC) class II (HLA-DR) antigens on M cells within follicle-associated epithelial cells (FAE) covering Peyer's patches was analyzed immunohistochemically. HLA-DR antigens were strongly expressed on M cells and cells with dendritic morphology, whereas other FAE covering Peyer's patches showed weak, but definite staining. Dendritic cells were also positive for S-100 protein and IL-1. These findings suggest that M cells as well as dendritic cells within FAE form an antigen-presenting cell system and contribute to the first information releaser for the mucosal immune system.

Somatic generation of diversity in a mammalian primary lymphoid organ: the sheep ileal Peyer's patches

Ileal Peyer's patches (IPPs) in the sheep are composed of tightly packed follicles in which surface IgM-positive B cells proliferate and can be exported to the periphery. We report that the light chain rearrangement pattern in a single IPP follicle is much more restricted than in the entire tissue, which indicates that, as in the chicken bursa, ongoing rearrangement does not take place in this organ. Moreover, we show that B cells extensively diversify their antigen receptor while proliferating in IPP follicles. Sequencing of part of the V lambda locus indicates that this diversification is not achieved by gene conversion, but rather by untemplated somatic mutation and intense selective pressure. These results strongly imply that sheep IPPs behave as a bursa-equivalent, primary lymphoid organ of diversification and that somatic point hypermutation, which is known to proceed during secondary immune responses, can also generate an antibody repertoire.

Secretory immunity in celiac disease: cellular expression of immunoglobulin A subclass and joining chain

Two-color immunofluorescence staining in situ demonstrated increased proportions of immunoglobulin A2 subclass-producing cells in jejunal mucosa from adult patients with untreated (47%, P less than 0.01) or treated (37%, P less than 0.05) celiac disease compared with controls (28%). Costaining was also performed for joining chain, which is a key factor in the epithelial transport of secretory antibodies; its expression by immunoglobulin A2 cells was only marginally reduced in untreated patients (96%) compared with treated patients and controls (98%). Also, immunoglobulin A1 cells showed similar joining chain positivity (89%) in all three groups. Considering the expanded total jejunal immunoglobulin A-cell population and the subclass-associated joining chain expression, it could be calculated that the potential of immunoglobulin A2 cells for contribution to secretory immunity was increased 3.9 times in untreated (P less than 0.01) and 1.8 times in treated (P less than 0.05) patients and that of immunoglobulin A1 cells was increased 1.7 times in untreated (P less than 0.05) but remained unaltered in treated patients. The estimated relative contributions of locally produced immunoglobulin A2 to secretory immunoglobulin A would thus be 51% and 37% in the two patient categories, respectively, compared with 31% in the controls. These data suggested enhanced secretory immunity in celiac disease and might reflect a protective, possibly antimicrobial, immune response. It could not be excluded, however, that increased generation of secretory immunoglobulin A at the same time contributes to the gluten-induced pathogenesis of celiac disease.