Immunological and biochemical characterization of an immunogenic antigen (5G8) of Giardia lamblia (MPF6P.648)

The protozoan parasite G. lamblia is an intestinal parasite of humans, which the World Health Organization estimates to have infected 250 million people worldwide. Clinical manifestations of G. lamblia infections vary from the asymptomatic carrier state to severe diarrhea, abdominal pain, nausea, malabsorption and weight loss. Our knowledge about the immunogenic antigens of G. lamblia is limited. The purpose of this study was immunologically and biochemically characterize an immunogenic antigen (protein 5G8) of G. lamblia . We generated monoclonal antibodies (moAbs) spe­cific to the protein 5g8 of the parasite by using splenocytes derived from in­fected mice. All of these moAbs recognized a protein of 71 kDa by Western blotting. This protein was isolated from a G. lamblia trophozoite lysate by affinity chromatography. The purified 71 kDa protein was analyzed by mass spectrometry. This immunogenic antigen was expressed inside of the G.lamblia trofozoites (>90% of total cell population) and only a small percentage (≈ 2-5%) of those trophozoites expressed high levels of the 5G8 protein on the cell surface. Trophozoite population expressing the 5G8 protein on the cell surface induced stronger antibody response that trophozoite population that does not express this protein on cell surface. The characterization of this antigen will provide a better understanding of the G. lamblia -host interaction, and will be important for developing effective control strategies against giardiasis.