Comparative studies on the roles of mediator molecules in expression of the suppressor activity of Mycobacterium avium complex‐induced immunosuppressive macrophages against T cell and B cell mitogenic responses

Summary Mycobacterium avium complex‐induced immunosuppressive macrophages (MAC‐MΦs) exhibit suppressor activity against c oncanavalin A‐induced T cell mitogenesis (T cell Con A mitogenesis). We examined the profiles of the MAC‐MΦ‐mediated suppression of lipopolysaccharide‐induced B cell mitogenesis (B cell LPS mitogenesis) and found the following. First, although N G ‐monomethyl‐L‐arginine and carboxy‐PTIO effectively blocked the MAC‐MΦ's suppressor activity against T cell Con A mitogenesis, MAC‐MΦ's action against B cell LPS mitogenesis was only weakly affected by these NO‐reducing agents. Second, B cell LPS mitogenesis was remarkably more susceptible to MAC‐MΦ‐derived reactive oxygen intermediates than T cell Con A mitogenesis. Third, B cell LPS mitogenesis was less susceptible to the inhibitory effects of the other MAC‐MΦ‐derived suppressor mediators, including free fatty acids, TGF‐β and prostaglandin E 2 , than T cell Con A mitogenesis. Fourth, MAC‐MΦ's suppressor activity was strongly dependent on B7‐1 like molecule‐mediated cell contact with target cells only in the case of T cell Con A mitogenesis. Therefore, there are significant differences in the modes of suppressor action of MAC‐MΦs against T cell and B cell mitogenesis.