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 cells (macrophages, Mphi) in the cultures and that an optimal PPD response occurred at a T/Mphi 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-treated similarly prepared B cells were in most instances effective in inducing a secondary TNP-specific response of in vitro-sensitized T cells.