The role of HLA-DR antigens in PPD-stimulated lymphocyte-monocyte interactions.

Autologous monocytes are required for an optimal lymphocyte proliferative response to purified protein derivate of tuberculin (PPD) in vitro and for a mixed lymphocyte culture induced by alloantigens. In the proliferative response to PPD we found that autologous monocytes could be replaced with HLA-DR-compatible monocytes and partly with HLA-DR semi-identical. In spite of a statistically significant difference between autologous and HLA-DR disparate monocytes in their cooperative capacity with PPD-stimulated lymphocytes, replacement in nearly one third of the cases was possible. These findings were supported by more detailed studies in which increasing numbers of allogenic and autologous monocytes were added to the isolated lymphocytes in the presence of PPD. It is concluded that the serologically defined HLA-DR antigens alone give insufficient information of the restriction elements controlling the PPD-stimulated lymphocyte-monocyte interactions.