Role of GP82 in the Selective Binding to Gastric Mucin during Oral Infection with Trypanosoma cruzi.

Oral infection by Trypanosoma cruzi has been the primary cause of recent outbreaks of acute Chagas' diseases. This route of infection may involve selective binding of the metacyclic trypomastigote surface molecule gp82 to gastric mucin as a first step towards invasion of the gastric mucosal epithelium and subsequent systemic infection. Here we addressed that question by performing in vitro and in vivo experiments. A recombinant protein containing the complete gp82 sequence (J18), a construct lacking the gp82 central domain (J18*), and 20-mer synthetic peptides based on the gp82 central domain, were used for gastric mucin binding and HeLa cell invasion assays, or for in vivo experiments. Metacyclic trypomastigotes and J18 bound to gastric mucin whereas J18* failed to bind. Parasite or J18 binding to submaxillary mucin was negligible. HeLa cell invasion by metacyclic forms was not affected by gastric mucin but was inhibited in the presence of submaxillary mucin. Of peptides tested for inhibition of J18 binding to gastric mucin, the inhibitory peptide p7 markedly reduced parasite invasion of HeLa cells in the presence of gastric mucin. Peptide p7*, with the same composition as p7 but with a scrambled sequence, had no effect. Mice fed with peptide p7 before oral infection with metacyclic forms developed lower parasitemias than mice fed with peptide p7*. Our results indicate that selective binding of gp82 to gastric mucin may direct T. cruzi metacyclic trypomastigotes to stomach mucosal epithelium in oral infection. Author Summary: Frequent outbreaks of acute Chagas' disease by food contamination with T. cruzi, characterized by high mortality, have been reported in recent years. In Brazil, oral infection is currently the most important mechanism of T. cruzi transmission. Studies on oral T. cruzi infection in mice have shown that insect-stage metacyclic trypomastigotes invade only the gastric mucosal epithelium and not other areas of mucosal epithelia prior to establishing systemic infection. Here we have shown that metacyclic trypomastigotes bind selectively to gastric mucin, a property also displayed by gp82, a metacyclic stage-specific surface protein implicated in cell adhesion/invasion process. It is also shown that the gastric mucin-binding property of gp82 resides in the central domain of the molecule and that the synthetic peptide p7, based on a gastric mucin-binding sequence of gp82, markedly reduces parasite invasion of cultured human epithelial cells in the presence of gastric mucin. These results, plus the finding that mice that received peptide p7 before oral infection with metacyclic trypomastigotes had fewer parasites replicating in the gastric mucosa and developed lower parasitemias than control mice, lead us to suggest that gp82-mediated interaction with gastric mucin may direct T. cruzi to stomach mucosal epithelium in oral infection. [ABSTRACT FROM AUTHOR]