Expression of HLA Class II Molecules on Human Monocytes and Dendritic Cells
By using a procedure for obtaining highly enriched dendritic cells (DRCs) and purified monocytes (MOs) from human peripheral blood, we have observed that the antigen-presenting cell (APC) function of human blood resides in the fibronectin receptor-positive, FcR-negative DRC population that lacks several monocyte/macrophage-specific differentiation antigens. On the other hand, purified MOs were not capable of presenting the soluble antigen PPD to T cells. To evaluate the expression of class II molecules from different loci (DR, DQ, and DP) on MOs and DRCs, binding of defined monoclonal antibodies (Mabs), specific for products of different HLA class II loci were quantitated by the use of 125I-F (ab′)2 anti-mouse Ig. On a per cell basis, MOs and DRCs expressed similar amounts of DR, DQ, and DP antigens (Table 1).