Dendritic cells are critical accessory cells for thymus-dependent antibody responses in mouse and in man.

We report that dendritic cells (DC) are necessary and potent accessory cells for anti-sheep erythrocyte responses in both mouse and man. In mice, a small number of DC (0.3-1% of the culture) restores the response of B/T-lymphocyte mixtures to that observed in unfractionated spleen. An even lower dose (0.03-0.1% DC) is needed if the T cells have been primed to antigen. Responses are both antigen and T cell dependent. Selective depletion of DC from unfractionated spleen with the monoclonal antibody 33D1 and complement ablates the antibody response. In contrast to DC, purified spleen macrophages are weak or inactive stimulators. However, when mixed with DC, macrophages can increase the yield of antibody-secreting cells about 2-fold. In man, small numbers (0.3-1%) of blood DC stimulate antibody formation in vitro. Purified human monocytes do not stimulate but in low doses (1% of the culture) inhibit the antibody response. Likewise, selective removal of human monocytes with antibody and complement enhances or accelerates the development of antibody-secreting cells. We conclude that DC are required for the development of T-dependent antibody responses by mouse and human lymphocytes in vitro.