Summary Several heat shock proteins (HSP) prime immune responses which are, in part, a result of activation of antigen presenting cells (APCs). APCs respond to these immunogenic HSPs by up-regulating co-stimulatory molecules and secreting cytokines including IL-1β. These HSP-mediated responses are central mediators in pathological conditions ranging from cancer, sterile inflammation associated with trauma and rheumatoid arthritis. We tested here the requirement of inflammasomes in the release of IL-1β by one immunogenic HSP, gp96. Our results show that murine APCs activate NLRP3 inflammasomes in response to gp96, by K+ efflux. This is shown to initiate inflammatory conditions in vivo, in the absence of additional known inflammasome activators or infection. These results document a novel mechanism by which proteins of endogenous origin, the HSPs, can modulate an inflammatory response following their release from aberrant cells.

The release of Heat Shock Proteins (HSPs) from aberrant cells can initiate immune responses following engagement of the HSPs with antigen presenting cells (APCs). This is an important mechanism for cancer immunosurveillance and can also be modeled by vaccination with HSPs through various routes, targeting specific APCs expressing the HSP receptor CD91. Immunological outcomes can be varied as a result of the broad expression of CD91 in different dendritic cell and macrophage populations. We investigated the cellular response of different APCs to the prototypical immunogenic HSP, gp96, in the context of Th1 immunity. Although APCs generally express similar levels of the HSP receptor CD91, we uncovered APC-distinct, downstream signaling pathways activating STAT1, and differential STAT1 induced genes. As a result of this differential and unique signaling we determined that gp96-activated macrophages, but not DCs are capable of activating NK cells to produce IFN-$$\gamma$$ γ . These data demonstrate that different APC subsets elicit unique intracellular signaling responses to HSPs which result in different patterns of downstream cellular activation and immune responses. Collectively this provides a novel tunable and autochthonous immune response to extracellular HSPs which has important implications on the development of immunity to cancer and infectious disease, as well as homeostasis.