Human dendritic cells: major stimulators of the autologous and allogeneic mixed leucocyte reactions.

Highly purified preparations of dendritic cells were obtained from human peripheral blood. Loosely adherent cells were selected and subsequently depleted of phagocytic cells and Fc receptor positive cells to yield the dendritic cell fraction. These isolates contained greater than 90% Ia positive cells, with many of the cells showing the morphological characteristics of the murine dendritic cell. These preparations were compared to other mononuclear cell fractions as stimulating cells in autologous and allogeneic mixed leucocyte reactions. The dendritic cell preparations provided the most potent stimulus for autologous T cell proliferation, with 10 x more 3H-thymidine incorporated by T lymphocytes incubated with autologous dendritic cells than with any other non-T cell preparation. Dendritic cells were also the most stimulatory cell in the allogeneic mixed leucocyte reaction, although the non-adherent subpopulation produced some stimulation of allogeneic T cells. In separate experiments, it was determined that B cells could be activated by pokeweed mitogen to vigorously stimulate autologous T cells. Visual observation of cluster formation in cultures containing dendritic cells and autologous T cells suggests that the capacity for intimate cell contact may be an important property of the dendritic cell in vivo.