ALTERATIONS INDUCED BY TRYPANOSOMA-CRUZI IN ACTIVATED MOUSE LYMPHOCYTES

Although a number of immunological anomalies have been shown to occur during the acute period of Trypanosoma cruzi infection, the contributi on of the parasite has not been clarified. In this work, we co-culture d activated splenic mononuclear cells (SMC) from normal outbred (CD1) or inbred (CBA/J) mice with purified T. cruzi trypomastigotes and stud ied ensuing T- and B- lymphocyte alterations. In the presence of paras ites, phytohaemagglutinin-stimulated SMC from either mouse background manifested a marked reduction in both lymphoproliferative capacity (i. e., H-3-thymidine incorporation) and cell membrane levels of interleuk in-2 receptors (IL-2R; determined by flow cytometry) relative to SMC f rom parasite-free cultures. Thus, substantial proportions of activated SMC either became unable to express detectable levels of IL-2R or exp ressed this receptor in significantly lower numbers than control SMC. Supernatants from T. cruzi suspensions reproduced these suppressive ef fects on phytohaemagglutinin-stimulated SMC from normal or chronically infected CD1 or CBA/J mice. Similar results were obtained with SMC ac tivated with a bacterial lipopolysaccharide. Since IL-2R expression is required for activated lymphocytes to progress through the cell cycle and multiply to mount effective immune responses, impaired IL-2R expr ession by T. cruzi provides a plausible hypothesis for the wide-ranged immunosuppression that occurs in the infected host.