Accessory-cell populations in the lymphoid tissues of fetal sheep were investigated following depletion ofB cells. An intraperitoneal injection of an anti-IgM antibody early in gestation resulted in a marked depletion of IgM+cells in lymphoid tissues. Immune and enzyme histochemical techniques were used to identify accessory-cellpopulations in the ileal Peyer's patch, spleen, and lymph nodes of B-cell-depleted fetal sheep. The rudimentaryfollicles in the ileal Peyer's patch showed strong enzyme reactivity for 5′ nucleotidase, indicating the presenceof follicular dendritic cells (FDCs). Enzyme reactivities for FDCs in primary follicles of the spleen and lymph nodeswere absent, as were reactivities for metallophilic macrophages in the marginal zone of the spleen. MgATPasereactivity associated with dendritic-cell populations in the gut-associated lymphoid tissues was detected.A monoclonal antibody against complement receptor-2 (CD21) reacted with FDCs in the rudimentary follicles ofthe ileal Peyer's patch and immature FDCs in lymph nodes. The results suggest that the development of accessory-cellpopulations in B-cell compartments of peripheral but not central lymphoid tissues is dependent on the presence of B cells.Peer Reviewe
