Flagellin induces antibody responses through a TLR5- and inflammasome-independent pathway.
Flagellin is a potent immunogen that activates the innate immune system via TLR5 and Naip5/6, and generates strong T and B cell responses. The adaptor protein MyD88 is critical for signaling by TLR5, as well as IL-1Rs and IL-18Rs, major downstream mediators of the Naip5/6 Nlrc4-inflammasome. In this study, we define roles of known flagellin receptors and MyD88 in Ab responses generated toward flagellin. We used mice genetically deficient in flagellin recognition pathways to characterize innate immune components that regulate isotype-specific Ab responses. Using purified flagellin from Salmonella, we dissected the contribution of innate flagellin recognition pathways to promote Ab responses toward flagellin and coadministered OVA in C57BL/6 mice. We demonstrate IgG2c responses toward flagellin were TLR5 and inflammasome dependent; IgG1 was the dominant isotype and partially TLR5 and inflammasome dependent. Our data indicate a substantial flagellin-specific IgG1 response was induced through a TLR5-, inflammasome-, and MyD88-independent pathway. IgA anti-FliC responses were TLR5 and MyD88 dependent and caspase-1 independent. Unlike C57BL/6 mice, flagellin-immunized A/J mice induced codominant IgG1 and IgG2a responses. Furthermore, MyD88-independent, flagellin-induced Ab responses were even more pronounced in A/J MyD88(-/-) mice, and IgA anti-FliC responses were suppressed by MyD88. Flagellin also worked as an adjuvant toward coadministered OVA, but it only promoted IgG1 anti-OVA responses. Our results demonstrate that a novel pathway for flagellin recognition contributes to Ab production. Characterization of this pathway will be useful for understanding immunity to flagellin and the rationale design of flagellin-based vaccines.
Department of Pathology, University of Washington, Seattle, WA 98195.
Américo Harry
AH
López-Yglesias
Xiaodan
X
Zhao
Ellen K
EK
Quarles
Marvin A
MA
Lai
Tim
T
VandenBos
Roland K
RK
Strong
Kelly D
KD
Smith
D000818:Animals; D020170:Caspase 1 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D005408:Flagellin / Q000235:genetics / Q000276:immunology*; D007070:Immunoglobulin A / Q000276:immunology; D007074:Immunoglobulin G / Q000276:immunology; D058847:Inflammasomes / Q000378:metabolism; D051379:Mice; D008805:Mice, Inbred A; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D053594:Myeloid Differentiation Factor 88 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D051616:Neuronal Apoptosis-Inhibitory Protein / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D010047:Ovalbumin; D017452:Receptors, IgG / Q000378:metabolism; D017472:Receptors, Interleukin-1 / Q000378:metabolism; D053724:Receptors, Interleukin-18 / Q000378:metabolism; D012486:Salmonella typhimurium / Q000201:enzymology / Q000235:genetics; D051198:Toll-Like Receptor 5 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*
C406563:IgG2c receptor; D007070:Immunoglobulin A; D007074:Immunoglobulin G; D058847:Inflammasomes; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; C496806:Naip5 protein, mouse; C496807:Naip6 protein, mouse; D051616:Neuronal Apoptosis-Inhibitory Protein; D017452:Receptors, IgG; D017472:Receptors, Interleukin-1; D053724:Receptors, Interleukin-18; D051198:Toll-Like Receptor 5; D005408:Flagellin; D010047:Ovalbumin; D020170:Caspase 1