Measurement of parasite-specific immune responses in vitro: evidence for suppression of the antibody response to Trypanosoma cruzi.

Using the Mishell and Dutton culture system, we have developed an assay for eliciting and quantifying parasite-specific immune responses in vitro. The ability of spleen cells from noninfected and Trypanosoma cruzi-infected mice to respond to parasite-associated antigens was assessed by examining the primary plaque-forming cell response to trinitrophenylated T. cruzi (TNP-TC). The response to TNP-TC of both normal, noninfected, unprimed mice and mice infected with T. cruzi is T cell dependent and appeared to involve recognition of parasite antigens by T. cruzi-specific T cells. In most experiments, spleen cells from infected mice respond to TNP-TC at levels equal to, or below, that of spleen cells from normal mice. This near "normal" response is in apparent contrast to the suppressed response of spleen cells from infected mice to another antigen (sheep red blood cells) or TNP on a different carrier (TNP-chicken erythrocytes). Demonstration that the response of spleen cells from infected mice to TNP-TC can be potentiated by addition of interleukin 2-containing supernatants or by depletion of plastic and Sephadex G-10-adherent cells suggests that the mechanisms which control the response of infected mice to nonparasite antigens may also limit parasite-specific immune responses.