Genetic control of isotype specific antibody responses to flagellin in mice (IRC4P.450)

Abstract Adjuvants can improve the efficacy of vaccines by inducing class-switched immune responses. Host factors controlling the magnitude of class-switched antibody responses are poorly understood. We have observed flagellin-immunized mouse strains differ in the magnitude of isotype specific antibody responses. Some strains are high responders (A/J, Swiss Webster) and other strains are low responders (C57BL6, Balb/c). All strains had comparable primary anti-flagellin IgM responses, suggesting common genetic variations influence isotype class switching. We hypothesized different genetic differences between A/J and C57BL/6 mice determine magnitude of responder phenotype. We bred C57BL/6 and A/J mice and tested F1 and F2 offspring for isotype specific antibody responses. Mice were immunized with a FliC protein mutated in the Naip5/6 recognition domain to overcome known differences in Naip5-dependent inflammasome activation between these mouse strains. We demonstrate anti-flagellin IgG1, IgG2a/c and IgA responses are inherited as a quantitative trait. Using consomic mice, we show the high responder phenotype is not controlled by the IgH locus on A/J chromosome 12. Using mutant flagellin proteins, we demonstrate the high responder phenotype is primarily controlled by the FliC D2/D3 domain. Understanding the host factors contributing to FliC D2/D3 induced antibody responses aid in the rationale design of vaccines, and help establish principles for future adjuvant design and development.