Purification and characterization of Giardia lamblia antigens in the feces of Mongolian gerbils.

In a recent study, we identified Giardia lamblia 65- and 70-kDa antigens in the feces of infected Mongolian gerbils. The 65-kDa antigen was from a strain isolated from a human with symptoms of giardiasis, and the 70-kDa antigen was from a strain isolated from a human with no symptoms of giardiasis. In this study, we used preparative electrophoresis and electroelution techniques to purify these antigens to a degree which showed a single discrete protein band on silver-stained polyacrylamide gels. By enzyme-linked immunoelectrotransfer blot, common epitopes on the 65- and 70-kDa antigens were indicated by their cross-reactivity with rabbit anti-65-kDa and anti-70-kDa sera. By indirect immunofluorescence assay, the cysts and trophozoites of the two strains cross-reacted with these sera. Of seven lectins tested, only concanavalin A bound to the 70-kDa antigen, suggesting a glycoprotein, and it possessed a low isoelectric point as assessed by preparative isoelectric focusing. Molecular mass estimations of these antigens by sodium dodecyl sulfate-polyacrylamide gradient gel electrophoresis were similar to the 65- and 70-kDa estimations obtained by native polyacrylamide gradient gel electrophoresis. Although the 65- and 70-kDa antigens proved to be resistant to 100 degrees C heat and stable in storage for up to 25 months at -20 degrees C, neither appeared to be the same as a fecal G. lamblia antigen with similar molecular mass found by other investigators. This suggests that variable G. lamblia antigens may be found in the feces of infected humans.