Trypanosome-derived oligopeptidase B is released into the plasma of infected rodents, where it persists and retains full catalytic activity

A trypsin-like serine peptidase activity, levels of which correlate,vith bl ood parasitemia levels, is present in the plasma of rats acutely infected w ith Trypanosoma brucei brucei. Antibodies to a trypanosome peptidase with a trypsin-like substrate specificity (oligopeptidase B [OP-Tb]) cross-reacte d with a protein in the plasma of trypanosome-infected rats on a Western bl ot. These antibodies also abolished 80% of the activity in the plasma of tr ypanosome-infected rats, suggesting that the activity may be attributable t o a parasite-derived peptidase. We purified the enzyme responsible for the bulk of this activity from parasite-free T. b. brucei-infected rat plasma a nd confirmed its identity by protein sequencing. We show that live trypanos omes do not release OP-Tb in vitro and propose that disrupted parasites rel ease it into the host circulation, where it is unregulated and retains full catalytic activity and may thus play a role in the pathogenesis of African trypanosomiasis.