Tissue localization of T and B lymphocytes in lagomorphs: Anatomical evidence for a major role of the gastrointestinal associated lymphoid tissue in generation of lymphocytes in the adult

Abstract

T and B cell domains are identified in rabbit lymphoid organs by immunofluorescence. The thymus is made up completely of T cells, the lymph node contains B cells in follicles and T cells in the diffuse cortex, the spleen contains B cells in the follicles of white pulp and T cells in the periaortic sheath with some overlap of T cells into B cell domains. The gastrointestinal lymphoid tissue contains a complex lymphoid cell organization. In the appendix at least seven zones may be recognized; T cells and B cells of different immunoglobulin classes are localized in different sites. T cells are localized in the dome overlying the follicles and thymus dependent area between the follicles. B cells of IgM, IgA, IgG and IgE classes are prominent in the center of follicles with lesser staining in the corona. The rim of the follicle contains null cells. The isthmus and mushroom submucosal tissue stain intensely for IgA, whereas IgE staining is less and IgM and IgG staining are very faint. These morphologic observations are consistent with other findings that suggest that the gastrointestinal lymphoid tissue is a major source of T and B cells in adult animals not only for the local production of secretory IgA and T cells which are released into the intestinal lumen but also for dissemination of T cells and B cells of other Ig classes to other lymphoid organs.