Differential antibody responses to Giardia lamblia strain variants expressing dissimilar levels of an immunogenic protein

Aims Giardia lamblia is a protozoan parasite that causes giardiasis, one of the most common worldwide gastrointestinal diseases. For rational development of a Giardia vaccine, increasing our understanding of the host‐Giardia interaction is crucial. In this study, we analysed the immunogenicity and antigenicity of two G lamblia strain variants [GS and GS‐5G8 (+)], which express different levels of the variant‐specific surface protein (VSP) 5G8 and also analysed the intestinal histological changes associated with Giardia infection. Methods and results We evaluated the antibody responses induced by G lamblia strains in infected, reinfected and immunized C3H/HeJ mice using ELISA, flow cytometry, Western blotting and histological analysis. Our results showed that G lamblia GS‐5G8 (+) was more immunogenic and antigenic than the GS strain. The antibody response against the GS‐5G8 (+) strain primarily recognized 5G8 protein. Serum antibody from infected and reinfected mice exhibited specific agglutination of trophozoites in vitro. GS‐5G8 (+)‐infected mice showed higher CD19+ infiltrating cell levels compared to GS‐infected animals. Conclusion G lamblia strains with different expression levels of an immunogenic antigen (VSP 5G8) induce differential antibody responses. A better understanding of the immunogenic proteins of G lamblia will contribute to the rational development of an effective vaccine against this parasitic disease.