Role of Hsp90 in CpG ODN mediated immunostimulation in avian macrophages

In mammals, CpG mediated immune activation is initiated through toll-like receptor (TLR) 9 and Hsp90 via activation of MAPK/ERK and PI3K/AKT pathways. However, in the absence of TLR9 ortholog in chicken genome, the role of Hsp90 and kinase (MAPK/ERK and PI3K/AKT) pathways in initiating CpG ODN2007 induced immune activation in chicken is not clear. Using electrophoretic mobility shift assay (EMSA) and selective inhibitors of signal transduction pathways, we determined the role of these pathways in the production of Th1 cytokines/chemokines and nitric oxide (NO) in CpG ODN2007 treated avian macrophage cells. Hsp90α but not Hsp90β is bound to CpG ODN2007. Inhibition of Hsp90 with geldanamycin resulted in the inactivation of MAPK/ERK and PI3K/AKT pathways leading to significantly reduced levels of IFN-γ, IL-6 and NO mRNAs in CpG ODN2007 stimulated cells. Moreover, inhibition of ERK1/2 and PI3/AKT kinase pathways with PD985009 and LY294002, respectively, suppresses the phosphorylation of ERK2 and AKT leading to the production of decreased amounts of IFN-γ, IL-6 and NO mRNAs in CpG ODN2007 stimulated cells. Our results demonstrate that binding of CpG ODN2007 to Hsp90 induces activation of ERK2 and AKT phosphorylation leading to the production of high levels of IFN-γ, IL-6, MIP-3α and nitric oxide (NO). In contrast to mammals, our results suggest that Hsp90α but not Hsp90β binds with the CpG ODN2007 and may play a major role in CpG ODN2007 induced immunoactivation in avian macrophage cells. To our knowledge, this is the first report evaluating the involvement of Hsp90 and kinase (MAPK/ERK and PI3K/AKT) pathways in CpG mediated immunostimulation in avian macrophage cells.