Dendritic cells in health and disease

Cells with a dendritic morphology that are rich in surface class II histocompatibility antigens (Ia antigens) but lacking in other lymphocytes or monocyte markers constitute a small (less than 1%) proportion of circulating mononuclear cells, but in inflammatory joint effusions they comprise up to 7% of the mononuclear population. Their role as accessory cells in normal autologous and allogenic mixed leukocyte reactions is reviewed and the possible contribution of dendritic cells to intra-articular immunologic processes is considered.