CpG DNA Induces Self and Cross-Hyporesponsiveness of RAW264.7 Cells in Response to CpG DNA and Lipopolysaccharide: Alterations in IL-1 Receptor-Associated Kinase Expression

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Abstract
Exposure of macrophages to LPS induces a state of hyporesponsiveness to subsequent challenge with LPS. It has not been known whether previous exposure to CpG DNA induces a similar suppressive response to subsequent stimulation with CpG DNA. In the present study, we demonstrate that pretreatment with CpG DNA induces suppression of cytokine release in a murine macrophage-like cell RAW264.7 in response to subsequent challenge by CpG DNA. Additionally, CpG DNA-mediated activation of mitogen-activated protein kinases, including c-Jun NH2-terminal kinase, extracellular signal-regulated kinase, and p38, and activation of transcription factors AP-1, CREB, NF-κB, and STAT1 are greatly suppressed in the cells pre-exposed to CpG DNA. Pretreatment with CpG DNA also partially inhibited LPS-mediated production of cytokines and activation of mitogen-activated protein kinases and transcription factors. Neither LPS nor CpG DNA treatment inhibited Toll-like receptor 4, MD2, Toll-like receptor 9, myeloid differentiation factor 88, Toll/IL-1R domain-containing adaptor protein, Tollip, and TNF-α receptor-associated factor 6 expression. Interestingly, CpG DNA or LPS stimulation led to the inhibition of IL-1R-associated kinase expression. These results indicate that CpG DNA-induced refractory of RAW264.7 cells may be, at least in part, due to suppressed IL-1R-associated kinase expression.