Effect of fixed epimastigote forms of Trypanosoma cruzi on the hemocytes and the prophenoloxidase-activating system of the crayfish Pacifastacus leniusculus.

The effect of the parasite Trypanosoma cruzi on the hemocytes and the prophenoloxidase (proPO)-activating system of the crayfish Pacifastacus leniusculus was studied. Incubation of the crayfish hemocyte lysate with fixed epimastigote forms of the parasites (4 x 10(5) cells/ml) induced a marked activation of the crayfish proPO system, measured as phenoloxidase activity. The activation of proPO by the parasite was much stronger (7-fold) than that induced by beta-1, 3-glucans (1 mg/ml) which are known to be efficient elicitors of the proPO system. The fixed parasites promoted the spreading and degranulation of different populations of the crayfish hemocytes isolated by Percoll gradients, and were often observed to be attached to the crayfish hemocytes in rosette-like fashion. The attachment of the epimastigote forms of T. cruzi to the crayfish blood cell surface was not dependent on the adhesive 76-kDa protein released by the crayfish hemocytes, since the exocytotic inhibitor SITS and monospecific antibodies to the 76-kDa protein did not prevent parasite adhesion. The crayfish hemocytes apparently are able to phagocytose the fixed epimastigote forms of T. cruzi in vitro.