Circulating factor from a kala-azar patient suppresses in vitro antileishmanial T cell proliferation

In vitro lymphocyte blastogenesis stimulated by phytohaemagglutinin (PHA), streptococcal antigens (SKSD) and leishmanial antigens were used to assess T cell responsiveness in one patient with kala-azar before and after therapy. During the illness, responses to PHA and SKSD but not to leishmanial antigens could be detected. After treatment lymphocytes responded to all three stimuli when cells were cultured in convalescent plasma, but failed to respond to leishmanial antigens when cultured in plasma obtained before treatment. These observations suggest the presence of a circulating inhibitor of anti-leishmanial T cell responsiveness in kala-azar, and warrant further investigation.