The Role of Gut‐associated Lymphoid Tissues in the Generation of Immunoglobulin‐bearing Lymphocytes in Sheep

Abstract

Summary. Experiments were designed to examine the relative contributions of Payer's patches and mesenteric lymph nodes to the population of circulating immunoglobulin-bearing lymphocytes in sheep. The ileum, with more than 9O' !' o of the total Peyer's patches, the mesenteric lymph nodes, or both, were removed from lambs at different stages of development and the composition of the cell populations in lymph from different sources and in the blood was examined. Lambs which had had the ileum removed before or within a few days of birth were deficient in small lymphocytes bearing membrane immunoglobulin. This deficit remained for at least the first year of the animals' lives. Neither the removal of mesenteric lymph nodes nor removal of the ileum had any statistically significant effect on the total output of cells or on the population of igA-producing cells in lymph draining from the gut.

The follicle‐associated epithelium of the ileal Peyer's patch in ruminants is distinguished by its shedding of 50 nm particles

“…These observations add to previous evidence suggesting a structural and functional maturation of PP before birth and their qualification as a primary lymphoid organ (8). There is evidence that the ileal PP is an important site for the primary generation of B cells in sheep (16). Handling of macromolecular tracers by its FAE is of interest in this context.…”

CD40 signalling in ileal Peyer's patch B cells: implications for T cell-dependent antigen selection

“…If this is true, then CD40 signalling may play a primary role in iPfB cell differentiation rather than iPfB cell proliferation. This conclusion would be consistent with observations that B cell emigration from the ileal PP increased markedly in lambs after birth (12), a time when antigen exposure occurs, and that B cell numbers were decreased in the blood of young lambs that had been thymectomized and were deficient in CD4 + T cells (28).…”

“…However, clustering of somatic mutations to the CDR regions of Ig X light chain V genes (18), the marked increase in iPfB cell emigration following birth (12) and the premature involution of ileal PP follicles in sterile gut-loops (19) could equally be interpreted as evidence that antigen, and perhaps T cells, do play a role in both iPfB cell proliferation and the selection of emigrant B cells. A T cell-dependent antigen selection of emigrant iPfB cells would further imply that the TCR repertoire 'shaped' the Ig repertoire of circulating B cells.…”

“…In young sheep, -70% of all B cells are located within lymphoid follicles of the ileal PP (11) and emigrant B cells make a major contribution to the B cell populations in all lymphoid tissues (12,13). The ileal PP follicular (iPf) B cells express membrane IgM and Ig light chain (14) but are phenatypically and functionally immature (15)(16)(17).…”

Antibody Repertoire Development in Fetal and Neonatal Piglets. XX. B Cell Lymphogenesis Is Absent in the Ileal Peyer’s Patches, Their Repertoire Development Is Antigen Dependent, and They Are Not Required for B Cell Maintenance

“…5). The failure of resection to reduce B cell levels is inconsistent with the pivotal report of Gerber et al (72). These investigators resected 1-2 m ileum of fetal, newborn, and 6-mo-old sheep and manually recorded the number of Ig + cells per 500 small lymphocytes in the draining lymph using a primitive slide smear method.…”