Sera from chronic Chagasic patients and rodents infected with Trypanosoma cruzi inhibit trans-sialidase by recognizing its amino-terminal and catalytic domain.

We investigated whether sera from chronic Chagasic patients and animals infected with Trypanosoma cruzi inhibit the removal of sialic acid from human erythrocytes and the transfer of sialic acid from sialyllactose to [14C]lactose in the reactions catalyzed by the parasite trans-sialidase. Sera from Swiss mice and Calomys callosus animals infected with three different T. cruzi strains inhibit both reactions. Inhibition increases during the infection, reaching maximal levels when the parasitemia decreases. Among 44 sera of untreated chronic Chagasic patients, 40 inhibit both reactions. Inhibition is observed with total, defatted sera or with purified immunoglobulins. Whereas most of the inhibitory antibodies from Chagasic patients react with the papain fragment of trans-sialidase in immunoblots, a few patients have noninhibitory antibodies that react only with the entire trans-sialidase. These findings may be relevant for the pathology of Chagas' disease.