Mechanism of cell invasion by Trypanosoma cruzi: importance of sialidase activity.

The sialidase activity of trypomastigotes of Trypanosoma cruzi and its relationship to the ability of different stocks of the organism to infect cultured cells was examined. Sialidase activity in lysates of trypomastigotes was confirmed and shown to be present in organisms of four different stocks of T. cruzi. In addition, sialidase activity was detected in sera of mice acutely infected with organisms of each of the stocks of T. cruzi examined. Erythrocytes from these mice were agglutinated by peanut lectin, suggesting sialidase activity in vivo. Treatment of normal mouse peritoneal macrophages with sera from acutely infected mice resulted in an increased capacity of the cells to internalize blood trypomastigotes. IgM or IgG antibodies specific to T. cruzi were not detected in the sera displaying sialidase activity. Treatment of parasites and/or normal mouse macrophages with Vibrio cholerae neuraminidase, however, had little effect in the rate of internalization of parasites. Treatment of L 929 mouse fibroblasts with neuraminidase reduced significantly the rate of infection of the cells with blood trypomastigotes. Anti-sialidase activity developed and was detected in sera of infected mice and humans, suggesting that the neuraminidase activity of the parasite may play a significant role in the invasion of host cells only during the initial phase of the infection.