TLR-mediated type I IFN induction in pDCs requires the rapamycin-sensitive PI3K-mTOR-p70S6K pathway

Robust type I interferon (IFN-alpha/beta) production in plasmacytoid dendritic cells (pDCs) is critical for anti-viral immunity. Here we demonstrated a role for the mammalian target of rapamycin (mTOR) pathway in regulating interferon production by pDCs. Inhibition of mTOR or the ‘downstream’ mediators of mTOR p70S6K1,2 kinases during pDC activation via Toll-like receptor 9 (TLR9) blocked the interaction of TLR9 with the adaptor MyD88 and the subsequent activation of interferon response factor 7 (IRF7), resulting in impaired IFN-alpha production. Microarray analysis confirmed that inhibition of mTOR by the immunosuppressive drug rapamycin suppressed anti-viral and anti-inflammatory gene expression. Consistent with this, targeting rapamycin-encapsulated microparticles to antigen-presenting cells in vivo resulted in a diminution of IFN-alpha production in response to CpG DNA or the yellow fever vaccine virus strain 17D. Thus, mTOR signaling plays a critical role in TLR-mediated IFN-alpha responses by pDCs. CpGA is a TLR9 agonist. pDCs were isolated from mouse spleen or human PBMC. The effect of rapamycin on pDCs IFN-alpha production as induced by TLR ligands was studied. The mechanism of rapamycin effect was dissected in RAW cell line.