Effects of type II alveolar epithelial cells on T cell mitogenic responses to concanavalin A and purified protein derivatives.

To investigate the role of type II alveolar epithelial cells during the T cell-dependent host immune response to Mycobacterium tuberculosis (MTB), effects of MTB-infected A-549 human type II alveolar epithelial cells (A-549 cells) on T cell mitogenesis in response to concanavalin A (Con A) and purified protein derivatives (PPD) were studied. Human peripheral blood mononuclear cells (PBMCs) were cocultivated with uninfected or MTB-infected A-549 cells and Con A-and PPD-induced T cell mitogeneses were examined, and the following findings were obtained. T cell mitogenesis was inhibited by uninfected as well as MTB-infected A-549 cells, even when a dual-chamber culture system was used to prevent direct cell contact between PBMCs and A-549 cells. Therefore, it appears that A-549 cells suppress T cell mitogenesis by producing some unknown humoral suppressor factors.