CIRCULATING TRANS-SIALIDASE ACTIVITY AND TRANS-SIALIDASE-INHIBITING ANTIBODIES IN TRYPANOSOMA-CRUZI INFECTED MICE

Parasite-derived trans-sididase (TS) activity was demonstrated in the serum and blood of Trypanosoma cruzi-infected mice. Serum TS activity levels correlated well with parasitemia in BALB/c and Swiss mice durin g the initial stages of the infection. However, in later stages the TS activity levels decreased despite increasing parasitemia. This coinci ded with the appearance of circulating TS antibodies. On the other han d, there was always a good correlation between TS activity and parasit emia in athymic nude mice. Sera from mice with high parasitemia and lo w TS activity inhibited TS activity in vitro. The inhibition was also observed with purified serum IgG, and it was absorbed by staphylococca l protein A, indicating that it was caused by anti-TS IgG antibodies. These antibodies inhibited the enzymatic activity of insolubilized TS, indicating that they act by interfering with the catalytic site rathe r than by aggregating the enzyme. The presence of inhibitory antibodie s, however, did not prevent the progression of parasitemia in BALB/c m ice.