Abundant empty class II MHC molecules on the surface of immature dendriticcells

A monoclonal antibody specific for the empty conformation of class II MHC m olecules revealed the presence of abundant empty molecules on the surface o f spleen- and bone marrow-derived dendritic cells (DC) among various types of antigen-presenting cells. The empty class II MHC molecules are developme ntally regulated and expressed predominantly on immature DC. They can captu re peptide antigens directly from the extracellular medium and present boun d peptides to antigen-specific T lymphocytes, The ability of the empty cell -surface class II MHC proteins to bind peptides and present them to T cells without intracellular processing can serve to extend the spectrum of antig ens able to be presented by DC, consistent with their role as sentinels in the immune system.