2‐AG limits Theiler's virus induced acute neuroinflammation by modulating microglia and promoting MDSCs

The innate immune response is mediated by primary immune modulators such as cytokines and chemokines that together with immune cells and resident glia orchestrate CNS immunity and inflammation. Growing evidence supports that the endocannabinoid 2‐arachidonoylglycerol (2‐AG) exerts protective actions in CNS injury models. Here, we used the acute phase of Theiler's virus induced demyelination disease (TMEV‐IDD) as a model of acute neuroinflammation to investigate whether 2‐AG modifies the brain innate immune responses to TMEV and CNS leukocyte trafficking. 2‐AG or the inhibition of its hydrolysis diminished the reactivity and number of microglia at the TMEV injection site reducing their morphological complexity and modulating them towards an anti‐inflammatory state via CB2 receptors. Indeed, 2‐AG dampened the infiltration of immune cells into the CNS and inhibited their egress from the spleen, resulting in long‐term beneficial effects at the chronic phase of the disease. Intriguingly, it is not a generalized action over leukocytes since 2‐AG increased the presence and suppressive potency of myeloid derived suppressor cells (MDSCs) in the brain resulting in higher apoptotic CD4+ T cells at the injection site. Together, these data suggest a robust modulatory effect in the peripheral and central immunity by 2‐AG and highlight the interest of modulating endogenous cannabinoids to regulate CNS inflammatory conditions.This work was supported by grants to CG, DC and MLR from Ministry of the Economy and Competitiveness (CG: MINECO SAF2013–42784‐R, SAF2016 76449‐R; MLR: SAF2013–48271, DC: PI15/00963), the Comunidad de Madrid (CG: S2010/BMD‐2308 and MLR: S2010/BMD‐2353), the Red Española de Esclerosis Múltiple (CG: REEM: RD12/0032/0008; RD16/0015/0021; FC: RD12/0032/12, DC: RD16/0015/0019) sponsored by the Fondo de Investigación Sanitaria (FIS), partially financed by F.E.D.E.R.; European Union “Una manera de hacer Europa” and ARSEP Foundation to DC. Diego Clemente's group was sponsored by ADEM‐TO, Aciturri Aeronáutica S.L. and Vesuvius Ibérica LA. M.M. is a senior postdoctoral supported by the Comunidad de Madrid (S2010/BMD‐2308) and hired by MINECO; DC and IM‐D are hired by SESCAM.Peer reviewe