Characterization of a membrane antigen of Leishmania amazonensis that stimulates human immune responses.

To investigate human immune responses to defined leishmania Ag we have begun to characterize biochemically and immunologically, an abundant 42-kDa surface Ag of Leishmania amazonensis, a causative agent of human leishmaniasis. We have shown that this Ag, La gp42, is expressed on the surface of L. amazonensis promastigotes, being anchored to the membrane by a glycosyl-phosphatidylinositol moiety. As demonstrated by lectin blotting studies, La gp42 is glycosylated, binding both Con A and wheat germ agglutinin. Immunologically, La gp42 is strongly recognized by sera from patients with different forms of leishmaniasis as well as by patients with Chagas' disease. In addition, we show that purified La gp42 stimulates the proliferation of human T lymphocytes obtained from several leishmaniasis patients. Finally, the N-terminal sequence of La gp42 was obtained and a serologically cross-reactive 42-kDa protein with a homologous sequence was identified in Leishmania major.