A study of modified lymphatics in the deep cortex of ruminant lymph nodes.

Ruminant lymph nodes, except when very small, were found to have a system of smooth-walled channels in the periphery of the 'deep cortical units' defined by Bélisle & Sainte-Marie (1981 a,b). Each channel originated with many 'blind' branches in the subnodular layer of the cortex and ended by joining a medullary sinus. The wall consisted of a continuous endothelial lining, a sometimes thin or discontinuous basement membrane without a basal lamina, and at least one layer of flattened reticular fibroblasts.

Ontogeny of reticular cells in the ileal Peyer's patch of sheep and goats.

The ontogeny of reticular cells in the ileal Peyer's patch of sheep from 70 days gestational age was studied by light and electron microscopy and by enzyme histochemistry. Small to medium-sized lymphocytes were seen in the lamina propria at 97 days, when the stroma was essentially still mesenchymal. By 110 days, the stromal cells in the dome/follicle primordia had differentiated into reticular fibroblasts, whose processes and fibers were seen to surround groups of lymphocytes.

The intestinal habitat for organized lymphoid tissues in ruminants; comparative aspects of structure, function and development.

Unlike the Peyer's patches of rats and mice, which are considered to be secondary lymphoid organs, the ileal Peyer's patch of sheep is thought to be responsible for the primary generation of B cells, like the bursa of Fabricius of birds. The ileal Peyer's patch of sheep shows prenatal maturation, antigen-independent lymphopoiesis, a rate of lymphocyte production larger than that of the thymus, and involution at a young age. Follicles contain few T cells and have an IgM+, relatively immature B lymphocyte population, as judged by B-cell differentiation markers.

Ontogeny, distribution and structure of aggregated lymphoid follicles in the large intestine of sheep.

Aggregates of lymphocytes were demonstrated from 70 days gestation (term 150 days in sheep) in the proximal colon and rectum. Immunoperoxidase staining for 5'-bromo-2'-deoxyuridine incorporation and IgM, indicated that the lymphocyte population of lymphoid follicles in fetal sheep colon was actively dividing and surface IgM positive. Enzyme histochemistry for 5'-nucleotidase showed that the lymphocytes developed in a meshwork of positive reticular cells, suggestive of developing follicles.

Organization of ruminant Peyer's patches as seen with enzyme histochemical markers of stromal and accessory cells.

Five enzyme histochemical reactions were used to characterize calf, goat kid and lamb Peyer's patches. 5'-nucleotidase and acid phosphatase gave a reticular pattern of staining in follicular and interfollicular regions, respectively. Different subpopulations of fibroblastic reticulum cells were suggested for the T cell area, the dome/corona region, and the follicle capsule.