Development of the follicle-associated epithelium and the secretory dendritic cell in the bursa of Fabricius of the guinea fowl (Numida Meleagris) studied by novel monoclonal antibodies

Two stromal elements, follicle-associated epithelium and secretory dendriti c cells of the bursa of Fabricius were studied by light microscopy and two novel MAbs, that were produced against splenic cell suspensions of guinea f owls. Both antigens recognized by these MAbs, designated GIIF3 and NICE, ar e localized in the cytoplasm of the stromal cells, and their molecular weig hts are 50 and 30 kD, respectively. During embryogenesis the GIIF3 and NICE cells emerge in the mesenchyme of the folds before follicle formation. The GIIF3 and the NICE-positive cells accumulate under the surface epithelium of the plicae and migrate into the epithelium, that precedes the bud-format ion. From the bud, the GIIF3-positive cells migrate up to the luminal surfa ce, and they transform to distinct, highly polarized follicle-associated ep ithelial cells. Single GIIF3-positive cells are also present in the interfo llicular epithelium. The NICE MAb recognized mesenchymal cells harbor in th e lymphoepithelial compartment of the folliculus, and they elaborate cytopl asmic granules. Around Day 20 of embryogenesis large amount of NICE-positiv e substance appear extracellularly in the medulla and around it. This perio d well correlates with the starting up of the bursal functions; clonal expa nsion of B cells, and generation of immune repertoire. After hatching the N ICE stainability diminishes, and it is restricted to the medullary bursal s ecretory dendritic cells. The NICE-positive, possibly elderly bursal secret ory dendritic cells, are capable for migration into the follicle-associated epithelium. In eight-day old birds some cells of the follicle-associated e pithelium reveals temporary NICE positivity, that may prove the transport o f the follicle-associated epithelial cells into luminal direction. By 12 we eks of age the presence of NICE-positive substance in the intercellular spa ce of the FAE, rather than in the cells of FAE may indicate the termination of the transport of secretory substance. In conclusion, two types of mesen chymal cells enter the surface epithelium of the bursal folds. The GIIF3-po sitive cells appear on the luminal surface of the follicles and occupy the place of the follicle-associated epithelial cells. The NICE-positive cells become secretory in nature and differentiate to bursal secretory dendritic cells. The follicle formation possibly, requires the joint presence of both GIIFS and NICE cells in the epithelium. Anat Rec 262:279-292, 2001. (C) 20 01 Wiley-Liss, Inc.