An 88,000-Mr Giardia lamblia surface protein which is immunogenic in humans

Human anti-Giardia lamblia sera specifically immunoprecipitated an 88,000-Mr surface protein from radioiodinated trophozoites, establishing this protein as a potentially important immunogen in humans. A mouse monoclonal antibody (GL-1) was isolated which immunoprecipitated the same 88,000-Mr surface protein recognized by the human sera. GL-1 gave uniform fluorescent staining of the cell surface and flagella of G. lamblia trophozoites from the Portland 1 and WB strains as well as fresh clinical isolates, but not of Giardia muris, suggesting that the surface antigen is specific to G. lamblia. Other human parasites, including Entamoeba histolytica, Trichomonas vaginalis, and Trichomonas hominis, were not stained. A second mouse monoclonal antibody (GL-2) gave weaker immunofluorescent staining of living G. lamblia trophozoites but intense staining of fixed cells. None of the other parasites tested were stained, with the exception of E. histolytica, which may contain a cross-reactive antigen. No proteins were recognized in immunoprecipitation studies with iodinated trophozoites.