Studies on the cellular immune responses of insects toward the insect pathogen Trypanosoma rangeli

Trypanosoma rangeli uses the same range of insect vector species as the human pathogen T. cruzi, but unlike the latter species, T. rangeli is pathogenic to some of its reduviid bug vectors. In this paper some aspects of the hemocytic responses of Rhodnius prolixus, a susceptible host/vector of T. rangeli, are examined and compared with those of two nonsusceptible insect species, the American cockroach, Periplaneta americana, and the desert locust, Schistocerca gregaria. In contrast to Rhodnius, Periplaneta and Schistocerca clear trypanosomes injected into the hemocoel. By 4 hr postinoculation large numbers of nodules, multicellular aggregates, are formed in the hemocoels of the cockroaches and the locusts, and the number of nodules formed is dose dependent. Trypanosomes are observable in the nodules, mostly intracellularly within lysosomes, and are in various stages of degeneration. Nodules are formed by the reduviid bug's hemocytes but only after the infection has lasted a few days and when free trypanosomes are abundant.