Microcirculation of intestinal lymphoid follicles in rat Peyer's patches.

Peyer's patch microvasculature carries recirculating lymphoid cells into lymphoid follicles and supports vigorous metabolic demands of crypts and replicating germinal centers. Scanning electron microscopy of methyl methacrylate casts of blood vessels in rat intestinal Peyer's patches revealed that ascending arterioles pierce follicles and feed to a subepithelial capillary network beneath the follicle surface. These capillaries interconnect with baskets of capillaries beneath adjacent crypts and flow into postcapillary venules in thymus-dependent areas around the follicle perimeters. This pattern is a modification of the fountain pattern in villi and reflects the secondary development of germinal centers of B lymphocytes between central ascending arterioles and peripheral postcapillary venules. Sections of glycol methacrylate-embedded follicles injected with India ink revealed multiple fine capillaries in germinal centers not detected by previous techniques. Capillary flow from follicle apex to adjacent crypts provides a route for feedback control of replenishment of the specialized antigen-trapping epithelium covering follicles, and it is an opportunity for absorbed materials and cellular products beneath the epithelium to modify migration of lymphocytes out of postcapillary venules into follicles.