THE RECEPTOR DEC-205 EXPRESSED BY DENDRITIC CELLS AND THYMIC EPITHELIAL-CELLS IS INVOLVED IN ANTIGEN-PROCESSING

DENDRITIC cells and thymic epithelial cells perform important immunore gulatory functions by presenting antigens in the form of peptides boun d to cell-surface major histocompatibility complex (MHC) molecules to T cells(1-3). Whereas B cells are known to present specific antigens e fficiently through their surface immunoglobins, a comparable mechanism for the capture and efficient presentation of diverse antigens by den dritic cells and thymic epithelial cells has not previously been descr ibed. We show here that their antigen-presentation function is associa ted with the high-level expression of DEC-205, an integral membrane pr otein homologous to the macrophage mannose receptor and related recept ors which are able to bind carbohydrates and mediate endocytosis. DEC- 205 is rapidly taken up by means of coated pits and vesicles, and is d elivered to a multivesicular endosomal compartment that resembles the MHC class II-containing vesicles implicated in antigen presentation. R abbit antibodies that bind DEC-205 are presented to reactive T-cell hy bridomas 100-fold more efficiently than rabbit antibodies that do not bind DEC-205, Thus DEC-205 is a novel endocytic receptor that can be u sed by dendritic cells and thymic epithelial cells to direct captured antigens from the extracellular space to a specialized antigen-process ing compartment.