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

Human Peyers patches (PP) were studied by immunohistochemistry to characterize functional properties of the follicle-associated epithelium (FAE) including the "membrane" (M) cells. The FAE had no transporting capacity for polymeric IgA (pIgA) because it did not express the secretory component (SC) which acts as a pIgA receptor. However, it expressed MHC class II (HLA-DR) determinants, except for the M cells (which were tentatively identified by absence of brush border alkaline phosphatase). It is possible, therefore, that the FAE generally performs class II-restricted transport and presentation to T cells of antigens which have been adequately processed in the gut lumen. The function of M cells may be limited to transport of particulate or undegraded antigens to subjacent macrophages for processing and subsequent presentation. There were significantly more intra- and subepithelial T cells in PP than in distant villi, and the T cells were concentrated adjacent to M cells. The proportion of the CD4+ phenotype (putative helper T cells) was much higher in FAE (approximately 40%) than in villous epithelium where the CD8+ (putative suppressor) phenotype predominated strikingly (approximately 90%). This disparity might reflect differences in capacity for positive and negative immune regulation at the two sites. The B cells terminating with Ig production in PP and adjacent to solitary lymphoid follicles apparently belonged to relatively mature memory clones as they showed a large proportion of IgG immunocytes and reduced J-chain expression. Conversely, both IgG and IgA immunocytes in lamina propria (LP) showed a high percentage of J-chain positivity (80-100%); such positivity was also considerable (45-60%) in mesenteric lymph nodes (MLN) in contrast to peripheral lymph nodes (PLN) and palatine tonsils (PT). Moreover, there was a decreasing percentage of IgA2 immunocytes in the order of PP (52%), distant ileal LP (40%), MLN (32%), PLN (11%), and PT (5%). Taken together, our results suggested that dissemination of relatively immature memory B-cell clones with high J-chain expression takes place from PP through MLN and that preferential settlement of such clones occurs in LP.