Signaling and the Inflammasome Mycobacteria through Mincle/CARD9 the Th17-Promoting Adjuvant Activity of Cord Factor and Peptidoglycan Recapitulate

Abstract

Although adjuvants are critical vaccine components, their modes of action are poorly understood. In this study, we investigated the mechanisms by which the heat-killed mycobacteria in CFA promote Th17 CD4 + T cell responses. We found that IL-17 secretion by CD4 + T cells following CFA immunization requires MyD88 and IL-1b/IL-1R signaling. Through measurement of Ag-specific responses after adoptive transfer of OTII cells, we confirmed that MyD88-dependent signaling controls Th17 differentiation rather than simply production of IL-17. Additional experiments showed that CFA-induced Th17 differentiation involves IL-1b processing by the inflammasome, as mice lacking caspase-1, ASC, or NLRP3 exhibit partially defective responses after immunization. Biochemical fractionation studies further revealed that peptidoglycan is the major component of heat-killed mycobacteria responsible for inflammasome activation. By assaying Il1b transcripts in the injection site skin of CFA-immunized mice, we found that signaling through the adaptor molecule caspase activation and recruitment domain 9 (CARD9) plays a major role in triggering pro–IL-1b expression. Moreover, we demonstrated that recognition of the mycobacterial glycolipid trehalose dimyco-late (cord factor) by the C-type lectin receptor mincle partially explains this CARD9 requirement. Importantly, purified pepti-doglycan and cord factor administered in mineral oil synergized to recapitulate the Th17-promoting activity of CFA, and, as expected, this response was diminished in caspase-1– and CARD9-deficient mice. Taken together, these findings suggest a general strategy for the rational design of Th17-skewing adjuvants by combining agonists of the CARD9 pathway with inflammasome activators. T he choice of adjuvants is often a critical factor in the success of vaccines, but the number of adjuvants available for clinical use is very limited. Effective adjuvants are known to act on the innate immune system to not only increase the magnitude of vaccine-induced immune responses, but also to direct the appropriate class of effector response (1). However, the innate immune pathways that must be targeted to elicit particular types of adaptive immunity are poorly understood, thus hampering the development of rationally designed adjuvants. Historically, mycobacteria and their components have been the basis of numerous adjuvants and immunotherapies. For instance, bacillus Calmette-Guérin instillation is widely used to treat superficial bladder cancer, and this attenuated mycobacterial strain has been employed as an adjuvant in experimental vaccines against Leishmania spp. and other pathogens (2). However, the best-known use of mycobacteria for stimulating the immune system is in CFA, a water-in-oil emulsion containing heat-killed Mycobacterium tuberculosis strain H37Ra or M. butyricum. Although not appropriate for human …

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Cite this paper

@inproceedings{Besra2013SignalingAT, title={Signaling and the Inflammasome Mycobacteria through Mincle/CARD9 the Th17-Promoting Adjuvant Activity of Cord Factor and Peptidoglycan Recapitulate}, author={Gurdyal S Besra and Vincenzo Cerundolo and Alan Sher Yamasaki and Xin Lin and Giorgio Trinchieri and Guangyou Feng and Sandy Oland and Sara Hieny and Pat Caspar and Sho Mayer-Barber and Sudagar S. Gurcha and Dragana Jankovic and Kevin Shenderov and Daniel L. Barber and Katrin D. Mayer-Barber and Carl G. Feng and Sho Yamasaki and Jenny P. -Y. Ting and Alan Sher}, year={2013} }