Both HLA-DR restricted and nonrestricted functions of adherent cells are required for induction of T lymphocyte proliferative responses.

There appeared to be two distinct functions of adherent cells in human T lymphocyte proliferative responses to purified protein derivative (PPD). The first is antigen-presenting ability which is mediated by antigen-presenting cells (APC) among adherent cells. By employing antiserum blocking pretreatment of APC, it was revealed that HLA-DR antigens are involved in this function and that identity or partial identity of HLA-DR antigens between APC and T lymphocytes is required for T lymphocyte antigen recognition. The second function is mediated by the soluble factor produced by adherent cells and is HLA-DR nonrestricted. Although it remains unclear whether APC and adherent cells producing the soluble factor belong to the same cell population, this second function might lead T lymphocytes to proliferative as long as T lymphocytes recognize antigen (PPD) via APC.