Natural and induced antibodies contribute to differential susceptibility to secondary cystic echinococcosis of Balb/c and C57Bl/6 mice.

Antibodies are key immune players in several helminth infections and animal models have been central for the identification of their mechanisms of protection. Murine secondary cystic echinococcosis is a useful model for studying Echinococcus granulosus immunobiology, being the immune profile mounted by the experimental host a determinant of parasite success or failure in infection establishment. In the present study, we analyzed infection outcome using Balb/c and C57Bl/6 mice strains, and compared their antibody responses in terms of quality and intensity. Our results showed that Balb/c is a highly susceptible strain to secondary cystic echinococcosis, while C57Bl/6 mice are quite resistant. Moreover, significant differences between strains were observed in natural and induced antibodies recognizing E. granulosus antigens, both at the systemic and peritoneal levels. Natural cross-reacting IgM, IgG2b and IgG3 antibodies were detected in sera from both strains but with different intensities, and - remarkably - natural IgG2b showed to be an intrinsic correlate of protection in both mice strains. Interestingly, naïve C57Bl/6 serum displayed a higher protoscolicidal activity, and heterologous - but not homologous - transference of C57Bl/6 naïve serum into Balb/c mice, significantly reduced their infection susceptibility. In the peritoneal cavity, different levels of natural cross-reacting IgM and IgG3 antibodies were detected in both mice strains, while cross-reacting IgG2b was detected only in C57Bl/6 mice. On the other hand, infected mice from both strains developed isotype-mixed antibody responses, with Balb/c mice biasing their response towards high avidity IgG1 and C57Bl/6 mice showing a predominance of mixed IgM/IgG2c/IgG2b/IgG3. In this regard, IgG1 levels showed to be a correlate of susceptibility in both mice strains. In conclusion, our results suggest that antibodies - either natural or induced - play a role in the susceptibility degree to murine secondary cystic echinococcosis.