HLA‐D‐restricted Antigen Activation of Sensitized T Lymphocytes: Studies on the Ability of HLA‐D/DR‐expressing B Lymphocytes to Substitute for Macrophages in Antigen Activation

The proliferative response of sensitized human T lymphocytes to purified protein derivative (PPD) and to trinitrophenyl (TNP)‐conjugated autologous cells in vitro is restricted by self HLA‐D/DR determinants. Here we report that the PPD‐specific response is strictly related to the content of phagocytosing celts (macrophages, M) in the cultures and that an optinal PPD response occurred at a T/M ratio between 10:1 and 5:1. B‐cell‐enriched suspensions, which also express the HLA‐D/DR determinants, were not able to replace the macrophages in this HLA‐D/DR‐restricted response. On the other hand, TNP‐trealed similarly prepared B cells were in most instances effective in inducing a secondary TNP‐specific response of in vitro‐sensitized T cells.