DENDRITIC CELLS FRESHLY ISOLATED FROM HUMAN BLOOD EXPRESS CD4 AND MATURE INTO TYPICAL IMMUNOSTIMULATORY DENDRITIC CELLS AFTER CULTURE IN MONOCYTE-CONDITIONED MEDIUM

A procedure has been developed to isolate dendritic cells to a high de gree of purity from fresh blood. Prior enrichment methods have relied upon an initial 1-2-d culture period. Purified fresh isolates lack the characteristic morphology, phenotype, and immunostimulatory function of dendritic cells. The purified cells have the appearance of medium s ized lymphocytes and express substantial levels of CD4, but lack the T cell molecules CD3, CD8, and T cell receptor. When placed in culture, the cells mature in a manner resembling the previously described, cyt okine-dependent maturation of epidermal dendritic cells (Langerhans ce lls). The cells enlarge and exhibit many cell processes, express much higher levels of major histocompatibility complex class II and a panel of accessory molecules for T cell activation, and become potent stimu lators of the mixed leukocyte reaction. Among the many changes during this maturation process are a fall in CD4 and the appearance of high l evels of B7/BB1, the costimulator for enhanced interleukin 2 productio n in T cells. These changes are not associated with cell proliferation , but are dependent upon the addition of monocyte-conditioned medium. We suggest that the freshly isolated CD4-positive blood dendritic cell s are recent migrants from the bone marrow, and that subsequent matura tion of the lineage occurs in tissues in situ upon appropriate exposur e to cytokines.