Regulation of antibody responses to flagellin by the innate immune system

Flagellin is the predominant component of the bacterial flagellum.  It is exposed on the surface of bacteria and is a major target of host immune responses. Flagellin has four domains: D0, D1, D2 and D3. The conserved D0 and D1 domains of flagellin are recognized by the innate immune system through multiple pathways, including TLR5, which recognizes the D1 domain, and Naip5/6, which recognizes the carboxyl end of the D0 domain. Preliminary data indicates that antibody responses are regulated by components of the innate immune system that confer flagellin recognition. IgG2c antibody responses in mice are dependent on MyD88, while IgG1 responses are independent of MyD88. We hypothesize that the conserved structural features of flagellin regulate these responses, and that TLR5 and Naip5/6 are the innate recognition pathways that determine Myd88-dependent IgG2c production.  My project aims are: 1) define the structural components of flagellin that determine antibody responses and 2) determine the innate immune pathways required for IgG1 MyD88-independendent response. To address these aims mice will be immunized with wild-type and mutant flagellin proteins that have non-functional recognition sites for TLR5 & Naip5/6. We will determine cytokine responses and measure isotype specific antibody responses against flagellin. Our results indicate that recognition of D0 and D1 domains are required for a robust IgG2c response. Moreover, there appears to be a third flagellin recognition pathway that is responsible for the MyD88-independent IgG1 responses. My project addresses fundamental principles in innate immune activation, antibody responses and the rational design of vaccine immunogens.