Psychological stress triggers the accumulation of myeloid-derived suppressor cells in the liver through adrenergic receptor signaling

Abstract Chronic physiological stress affects tightly regulated crosstalk between the nervous and the immune system. However, the exact mechanism(s) of stress-induced immunomodulation is far from clear. Immature myeloid cells such as myeloid-derived suppressor cells (MDSCs) impair immune responses, which may in turn increase susceptibility to infections and cancer or their complications. In a mouse model of chronic psychological stress through physical restraint, we found mononuclear-MDSC (Mo-MDSC) cells, defined as CD11b +Ly6C highLy6G highcells, to accumulate in the liver. These cells expressed high levels of Mo-MDSC markers such as CD14, TLR4, IL-4Rα as well as markers indicative of anti-apoptotic and immunosuppressive functions (HIF-1α, G-CSFR, Bcl2, Arg2, iNOS). In addition, FACS sorted MDSCs suppressed production of IFN-ɣ by T cells in vitro. Increased levels of proinflammatory mediators were detectable in serum samples of stressed mice, with circulating levels of IL-6 and G-CSF being the most pronounced mediators. The observed intrahepatic accumulation of Mo-MDSC-like cells was mediated by IL-6 and G-CSF and could be reversed by treatment with corresponding receptor-blocking monoclonal antibodies. In addition, this phenomenon was driven by norepinephrine (NE), the main neurotransmitter released from sympathetic neurons, and could be recapitulated by in vivo administration of NE to non-stressed mice. Our work reveals a novel mechanism of immunosuppression that is governed by adrenergic and inflammatory cues and alters the cellular landscape of the liver with implications for immune surveillance against microbes and cancer. This work was funded by NSERC