Flagellin is a potent immunogen that is recognized by TLR5 and Naip5/6, activates the innate immune system, and elicits strong T and B cell responses. The adaptor protein MyD88 is critical for both TLR5, as well as IL-1β and IL-18 receptors, major downstream mediators of the Naip5/6. Herein, we define the role of known flagellin receptors and MyD88 in antibody responses generated towards flagellin. To characterize the innate immune components that regulate isotype specific antibody responses, we used several genetically deficient mice: Naip5, caspase-1, MyD88, and TLR5/caspase-1. Using purified flagellin from S. Typhimurium, we tested serum cytokine responses in mice after i.p. injections. We observed that serum levels of IL-12/23p40 were TLR5-dependent, IL-18 levels were Naip5-dependent, and KC and IL-6 levels were dependent on both. We dissected antibody responses produced towards both flagellin and OVA via a prime/boost regimen. We show that IgG2c responses towards flagellin are TLR5-, and inflammasome-dependent. While IgG1 levels were partially dependent on TLR5 and the inflammasome, a substantial IgG1 response was induced through an undefined pathway. Conversely, the adjuvant effects of flagellin extrinsic antigen OVA are TLR5 and inflammasome dependent. Our results demonstrate a novel third pathway of flagellin recognition that contributes to antibody production. Further characterization of this pathway will be useful for flagellin-based vaccine design.
- Copyright © 2013 by The American Association of Immunologists, Inc.