Differentiation of the follicle-associated epithelium in ileal Peyer's patch and production of 50-nm particles are maintained in B-cell-depleted fetal sheep

To evaluate the dependence of the differentiation of the follicle-associated epithelium (FAE) on the presence of follicular B-cells, the FAE of ileal Peyer's patch follicles was examined in B-cell-depleted fetal lambs. The FAE of these rudimentary follicles, which are devoid of lymphocytes, showed normal differentiation, including carbonic anhydrase reactivity and ultrastructural characteristics of transcytosis, extensive interdigitation of the lateral plasma membrane and the shedding of membrane-bounded particles, approximately 50 nm in size, resembling exosomes. These 50-nm membrane-bounded particles were abundant in the extracellular space of the epithelium and the dome but no particles were found in the rudimentary follicles. This study confirms that the rudimentary follicles consist of clusters of follicular dendritic cells. Our findings suggest that the differentiation of FAE of ileal Peyer's patch and the production of the 50-nm particles constitute features that appear to be independent of B-cells.