A comparative study of the gut-associated lymphoid tissue of primates and rodents

Mouse and human intestinal immunity: same ballpark, different players; different rules, same score

The study of animal immune physiology and animal models of human disease have accelerated many aspects of translational research by allowing direct, definitive investigations. In particular, the use of mice has allowed genetic manipulation, adoptive transfer, immunization, and focused cell and tissue sampling, which would obviously be unthinkable for studies in humans. However, the disease relevance of some animal models may be uncertain and difficulties in interpretation may occur as a consequence of immunological differences between the two species. In this review, we will consider general differences in the structure and development of human and mouse mucosal lymphoid microenvironments and then discuss species differences in mucosal B- and T-cell biology that relate to the current concepts of intestinal immune function.

Normal structure, function, and histology of mucosa-associated lymphoid tissue

The mucosa-associated lymphoid tissue (MALT) initiates immune responses to specific antigens encountered along all mucosal surfaces. MALT inductive sites are secondary immune tissues where antigen sampling occurs and immune responses are initiated. Effector sites, present as diffuse lymphoid tissue along all mucosal surfaces are the sites of IgA transport across the mucosal epithelium. Though there are many differences between inductive sites in various organs, they all contain the same basic compartments-follicles, interfollicular regions, subepithelial dome regions, and follicle-associated epithelium. The morphologic differences between MALT and other secondary lymphoid tissues, between the MALT sites of differing anatomic locations, and species differences among laboratory animals are described. The morphologic changes in MALT associated with aging, route of nutrition, and genetic mutation (i.e., the nude and SCID mutations) are also discussed. MALT tissues comprise the mucosal immune system which can function independently of the systemic immune system and are, therefore, an important and often overlooked aspect of immunopathology.

IGHV1, IGHV5 and IGHV7 subgroup genes in the rhesus macaque

The diversity of the antibody response is achieved, in part, by rearrangement of different immunoglobulin (Ig) genes. The Ig heavy chain is made up of a variable region (IGHV), a diversity region (IGHD) and a joining region (IGHJ). Human germline IGHV genes have been grouped into seven multigene subgroups. Size and usage of these subgroups is not equal, the IGHV3 subgroup is the most commonly used (36%), followed by IGHV1/7 (26%), then IGHV4, IGHV5, IGHV2, IGHV6 (15%, 12%, 4%, 3% respectively). The rhesus macaque (Macaca mulatta) is a useful non-human primate model for studies of infection and the database of germline Ig genes for the macaque is gradually growing to become a useful tool in the study of B-cell responses. The proportions of IGHV subgroup usage in the macaque are similar to those in man. Representatives from IGHV3 and IGHV4 subgroups for the macaque have been published, as have germline sequences of the IGHD and IGHJ genes. However, to date there have been no sequences published from the second largest IGHV subgroup, IGHV1. We report the isolation and sequencing of a genomic fragment containing an IGHV1 gene from the macaque. Polymerase chain reaction (PCR) primers designed from this sequence enabled us to amplify and sequence 25 new IGHV1 germline genes. We also isolated two IGHV7 genes, using the same primers, and two IGHV5 genes, using human IGHV5 primers.

Immunohistochemical analysis of ageing human B and T cell populations reveals an age-related decline of CD8 T cells in spleen but not gut-associated lymphoid tissue (GALT)

It is thought that senescence of the immune system is responsible, at least in part, for many health problems associated with ageing. Previous studies on changes in lymphocyte composition have used flow cytometry to study peripheral blood lymphocytes (PBL's), or cells isolated from rodent tissue, and have yielded conflicting results. We have used immunohistochemistry to determine whether the B and T cells in human tissue from spleen and gut are affected by age. Areas of germinal centre, mantle zone and marginal zone of B cell follicles were measured. In addition, CD4 and CD8 T cells in T cell areas and in B cell follicles were counted. We observed a striking age-related decrease in the proportion of CD8+ T cells in the T cell zones of the spleen. This decrease was not apparent in the T cell population that occupies splenic B cell areas, or in GALT. Further differences, in CD4+ cells, were seen between T cell populations in the T cell zones and those in B cell areas. These findings highlight differences between lymphocyte populations in different lymphoid tissues, and different compartments within each tissue, which may be of importance in future studies of the ageing immune system.

Morphological characteristics of the ileal Peyer's patches in the rhesus macaque: a histological and ultrastructural study

Ileal Peyer's patches of rhesus macaques were investigated by light and electron microscopy (scanning-electron microscopy, transmission-electron microscopy). The results were compared with findings in other species. Differences were found concerning the shape of the dome area, the composition of the dome epithelium and the apical membrane of M cells: in the rhesus monkey, hemispherical domes bulge into the intestinal lumen. The dome epithelium is composed of three populations of gut epithelial cells; absorptive enterocytes as the predominant cell type; goblet cells; and M cells ("microfold bearing' or "membraneous' gut epithelial cells). The apical membrane of M cells forms irregular protrusions.

Selective biopsy of human Peyer's patches during ileal endoscopy

During routine lower gastrointestinal endoscopy of children for suspected chronic inflammatory bowel disease, it is possible to visualize lymphoid follicles (Peyer's patches) in the last few centimeters of the terminal ileum. Biopsy specimens have been taken from these Peyer's patches and the lymphoid cells have been isolated by collagenase digestion. The mean cell yield of Peyer's patch cells was 1.7 x 10(8) lymphocytes/g tissue. Isolated Peyer's patch cells were 26%-54% CD3+ (pan T cells), 14%-34% CD4+ (helper/inducer T cells), and 9%-17% CD8+ (suppressor/cytotoxic T cells). Twenty six percent to 48% of the Peyer's patch cells were B cells; less than 1% contained cytoplasmic immunoglobulin A. When stimulated in vitro with phytohemagglutinin or pokeweed mitogen, cells from Peyer's patches proliferated. The successful isolation of functional cells from Peyer's patches will now allow studies to be done at the afferent limb of mucosal immunoregulation in humans.

Immunology of gastrointestinal lymphoma

Experimental work showing that IgA plasma cell precursors activated in gut associated lymphoid tissue (GALT) of rats and sheep migrate to the lamina propria of the gut via the regional lymphatics, mesenteric lymph node and blood, has been supported by immunohistochemical studies. In rats, immunoblasts with cytoplasmic IgA are present in the Peyer's patches in association with the high endothelial venules which is probably an important, though not the only, site of extravasation into the gut, whereas cells with cytoplasmic IgA are rarely observed in the dome regions of Peyer's patches. Immunohistochemical studies of human Peyer's patches have revealed differences between the distribution of cells with cytoplasmic IgA in man compared to rats. In man, immunoblasts with cytoplasmic IgA are not concentrated in the zone of cells containing the high endothelial venules, whereas they are present in the dome regions of the Peyer's patches. The following questions arise: Do precursors of IgA plasma cells activated in human GALT migrate to the lamina propria via the blood, but extravasate predominantly via the capillary network, rather than the high endothelial venules? or do IgA plasma cell precursors 'mature' in situ in the Peyer's patches of man and subsequently migrate laterally to seed the lamina propria? Three lines of evidence from studies of primary B cell lymphomas of GALT support the latter hypothesis: 1) Primary B cell lymphomas of the gut remain localized to GALT for long periods of time; 2) Histological studies of the lymphoid tissue in these lymphomas have shown a gradation of cell types, from the muscularis mucosae towards the mucosal epithelium, which strongly suggests that plasma cells develop in situ in the gut from the adjacent layers of cells; 3) Preliminary studies of DNA extracted from the blood-borne cells from patients with GALT-derived B cell lymphoma have failed to demonstrate the presence of clonal gene rearrangements. Normal and malignant human GALT contains a perifollicular population of B cells with centrocyte-like morphology which lack surface IgD. No direct equivalent can be detected in rodent Peyer's patches. Their quiescent nature and distribution in malignant GALT suggests that they are follicle centre cell-derived and precursors of immunoblasts and plasma cells. As such they may be memory B cells. Their association with epithelium is a consistent feature of normal and malignant GALT which is of unknown but undoubted significance. The function of intraepithelial T cells is still unknown. Malignant T cells in MHI may be derived from intraepithelial T cells.(ABSTRACT TRUNCATED AT 400 WORDS)