Antigen recognition by effector T cells in antileishmanial defense

We have observed that T cells (Ly1+2-) from draining lymph nodes of mice that have footpad infections with Leishmania major activate macrophages for antileishmanial effects in vitro in an apparently contact-dependent, noncytotoxic manner. The nature of antigenic specificity in this system was investigated. Whereas lymphocytes sensitized to L. major induced antileishmanial effects in macrophages infected with L. major, lymphocytes sensitized to Listeria monocytogenes were ineffective. When macrophages infected with L. major were primed with listerial antigens, however, the lymphocytes sensitized to Listeria induced antiparasitic effects in an apparently lymphokine-independent manner. Furthermore, lymphocytes sensitized to one Leishmania spp. activated macrophages for in vitro defense against both homologous and heterologous Leishmania spp. These findings suggest that antigen recognition in macrophage activation for antileishmanial defense is critical and is restricted to the initial interaction of effector lymphocytes and macrophages. Recognition of genus-conserved antigens apparently can serve to trigger effector T cells to activate antileishmanial defense in macrophages.