Immunocytochemical study of the ontogeny of Peyer's patches in the Brazilian marsupial Didelphis albiventris.

A detailed ontogenetic immunocytochemical study is reported on gut-associated lymphoid development in the Brazilian marsupial Didelphis albiventris. This employed antibody probes raised to evolutionarily conserved peptides which have been shown to detect HLA-DR-like (class II MHC) antigens and T and B cell markers in a wide range of animal species. Cells with macrophage and dendritic morphology expressing class II MHC and a few cells expressing the T cell marker CD3 were found in the lamina propria of duodenal villi in early (approximately 24 mm crown-rump length) latent opossum. Cells with B cell markers were not detected until lactent animals reached > 60 mm. Development of Peyer's patches (PP) was seen first in the duodenum in 45-60 mm lactent animals, progressing to well developed PP in the duodenum and ileum in lactent animals > 80 mm. These PP, like those in weanling and juvenile animals, consisted of follicles with a network of class II MHC positive dendritic cells and round cells lacking T and B markers, but lacking well defined mantle zones. B cells were present mainly in the lymphatic sinuses, with CD3 T cells present between follicles in the PP and intraepithelially in the villi. The study reveals the sequential development of class II MHC positive dendritic cells, T cells and B cells in the intestinal ontogeny of the opossum PP. These features occurred initially exclusively in the duodenum and subsequently in the ileum, paralleling the physiological maturation of the gut in eutheria.