Synthesis of iNOS and NO by MO-MDSCs are attributed to IFN-γ signaling through

STAT1 [4]. To determine if this pathway is active, B16- and 4T1-induced MDSCs were examined for STAT1 phosphorylation. CD11b+Gr1+ MDSCs from wild type, but not from IFN-γR−/− mice, expressed IFN-γR and IFN-γ-deficiency did not affect expression of IFN-γR (Supporting Information Fig. 2). IFN-γ-treated MDSCs from wild-type and IFN-γ−/− mice, but not from control IFN-γR−/− mice, contained phosphorylated STAT1 (Fig. 3C) indicating that MDSCs have the potential to respond to IFN-γ. Production of arginase has been attributed to IL-4 and IL-13 signaling through the common γ and IL-4Rα chains [9, 26]. Stimulation of MDSCs from wild type, but not from IL-4Rα−/− mice with IL-4, activated STAT6 (pSTAT6, where pSTAT6 is defined as phosphorylated selleck kinase inhibitor STAT6) (Fig. 3C), demonstrating that MDSCs have the potential to respond to IL-4 through IL-4Rα. These studies demonstrate that although MDSCs can respond to IFN-γ and IL-4, IFN-γ and IL-4Rα do not regulate MDSCs accumulation, phenotype, or suppression. Therefore, targeting IFN-γ and/or IL-4Rα will not reduce the quantity SRT1720 in vivo of MDSC, alter MDSC phenotype, or restore T-cell activation.

MDSC production of IL-10 and macrophage-induced MDSC production of IL-10 are partially regulated by IFN-γ and IL-4Rα. However, targeting these molecules is unlikely to facilitate polarization toward a type 1 response because the minimal reduction in MDSC production of IL-10 will not

restore macrophage production of IL-12. Therefore, treatments that downregulate IFN-γ and/or IL-4Rα are unlikely to be therapeutically effective. Breeding stock for BALB/c, transgenic medroxyprogesterone D011.10 (TcR is I-Ad-restricted, ovalbumin (OVA) peptide323-339-specific), transgenic OT-1 (TcR is H-2Kb-restricted, OVA peptide SINNFEKL-specific), IFN-γR-deficient C57BL/6, IFN-γ- deficient C57BL/6, IFN-γ-deficient, and IL-4Rα-deficient BALB/c, and BALB/c Clone 4 (H-2Kd-restricted, influenza hemagglutinin peptide518–526-specific) mice were from The Jackson Laboratory (Bar Harbor, ME, USA) or maintained in the UMBC animal facility. IFN-γR-deficient BALB/c mice were generated from 129-IFN-γR−/− mice (The Jackson Laboratory) by backcrossing to BALB/c for 12 generations. PCR screening was performed as described (http://jaxmice.jax.org/protocolsdb/f?p=116:2:1442124967609278::NO:2:P2_MASTER_PROTOCOL_ID,P2_JRS_CODE:7034,002702). Pups from the F12 generation were intercrossed and PCR screened to identify homozygous BALB/c IFN-γR−/− mice. Mice were bred in the UMBC animal facility. All animal procedures were approved by the UMBC Institutional Animal Care and Use Committee. Fluorescently-coupled Gr1 (clone RB68C5), CD11b, Ly6C (clone AL-21), Ly6G (clone 1A8), IL-4Rα, IFN-γR, CD115, F4/80, CD3, CD4, CD8, DO11.10 TCR (clone KJ1-26), Vβ8.1&8.