The follicle-associated epithelium in the bursa of Fabricius cell origin studied by means of quail-chick chimeras and monoclonal antibodies.

The cell origin of the follicle-associated epithelium (FAE) of the bursa of Fabricius was studied by two different technical approaches. Precolonized quail bursal rudiments were grafted into chick embryos and the grafts were recovered 2 wk after hatching of the recipients. By taking advantage of the distinct nuclear characteristics of chick and quail cells, it could be shown that the specialized FAE consists of a mixture of epithelial cells, with special features, among which hemopoietic cells, originating from the host, are dispersed. Staining of chicken bursas with different monoclonal antibodies reacting either with the epithelial component (BEP-1) or with the hemopoietic cells of the bursa (L22, L17) confirmed that hemopoietic cells, presumably macrophages, are mixed with the epithelial cells at the level of FAE.