T‐lymphocyte requirement for the induction of mouse macrophage procoagulant activity by Trypanosoma brucei

Summary We have previously shown that peritoneal macrophages from Trypanosoma brucei infected mice, but not from uninfected mice, expressed high levels of procoagulant activity that could not be produced in vitro by incubation of unstimulated macrophages with bloodstream forms of trypanosomes. In the present study we demonstrate that trypanosome‐induced macrophage activation can be achieved in vitro by providing either sensitized (day 7 of infection) lymphocytes and trypanosomes or the supernatant fluid from this interaction. The ability of lymphocytes to secrete macrophage‐activating lymphokines is enhanced up to day 12 of infection but was absent in the later stages. Although enhancement of the procoagulant activity occurred in infected nude mice, it seems that macrophage function in African trypanosomiasis, as regards the expression of procoagulant activity, is regulated by T‐lymphocytes.