Anti-alpha-galactosyl antibodies in chagasic patients. Possible biological significance.

1. Antibodies from Chagasic patients (Ch), bound to a column of immobilized purified glycoprotein 25-kDa antigen of Trypanosoma cruzi epimastigotes (gp25), were partially lytic (70% lysis at 50 micrograms/ml) to cultured metacyclic trypomastigotes (Y strain) in a complement-mediated reaction (alternative pathway). 2. Antibodies (Ch) eluted with galactose from a melibiose-Agarose column reacted in ELISA titration plates with gp25, whole cells of metacyclic trypomastigotes (Y strain), and less intensely with aqueous extracts of either T. cruzi (CL-14 strain) or Herpetomonas muscarum. 3. Agglutination of rabbit erythrocytes by anti-Gal antibodies from Chagasic patients or normal human sera (NHS) was inhibited by galactose and alpha-but not beta-anomeric galactosides. 4. Anti-Gal antibodies (Ch or NHS) were lytic to metacyclic trypomastigotes in complement-mediated reactions. 5. Agglutination of rabbit red cells by a serum sample from a T. cruzi-infected Rhesus monkey was inhibited by laminin. This serum was also lytic to metacyclic forms of T. cruzi (Y strain) involving the alternative complement pathway (70% lysis at 1:20 final dilution). 6. These results open the possibility of using anti-Gal antibodies for protection against infection by virulent T. cruzi.