Identification of a novel dendritic cell-like subset of CD64(+)/CD16(+) blood monocytes

Human monocytes (Mo) consist of a major subset of Fc gamma -receptor I (CD6 4)-positive typical low accessory phagocytes, and a minor CD64(-) DC-like s ubset with high T cell-accessory and IFN-alpha -releasing activity. Both po pulations also differentially express CD16 (Fc gamma -receptor III). Double labeling with anti-CD64 and anti-CD16 mAb, as performed here, identified f our different subsets. The CD64- subset consists of CD64(-)/16(+) cells wit h high antigen-presenting cell (APC) function and macrophage-like phenotype , and a CD64(-)/16(-) subset of less active APC but which exhibits a higher mixed lymphocyte reaction (MLR) stimulating and IFN-alpha -producing capac ity, possibly resembling plasmacytoid dendritic cell type II (DC2) blood pr ecursors. As well as the majority of CD64(+) cells that appeared CD64(+)/16 (-) and represent typical low-accessory, CD14(high) Mo, We could identify a nd describe a novel minor subset of CD64(+)/16(+) cells which is unique in combining typical DC and Mo characteristics in the same cell. These are hig h IL-12 production, high accessory capacity far antigen- or allogen-activat ed lymphocytes, and high expression of HLA-DR, CD86, and CD11c.