Reduced cutaneous CD200:CD200R1 signalling in psoriasis enhances neutrophil recruitment to skin

Abstract The skin immune system is tightly regulated to prevent inappropriate inflammation in response to harmless environmental substances. This regulation is actively maintained by mechanisms including cytokines and cell surface receptors and its loss results in inflammatory disease. In the case of psoriasis, inappropriate immune activation leads to IL-17-driven chronic inflammation, but molecular mechanisms underlying this loss of regulation are not well understood. We reveal that immunoglobulin superfamily member CD200, and signalling via its receptor, CD200R1 are reduced in non-lesional psoriasis skin. To examine the consequences of this, CD200R1 was blocked in a mouse model of psoriasis demonstrating that the receptor limits psoriasis-like inflammation. Specifically, CD200R1 blockade enhances acanthosis, CCL20 production and neutrophil recruitment but surprisingly, macrophage function and IL-17 production were not affected, and neutrophil reactive oxygen species production was reduced. Collectively, our data show that CD200R1 affects neutrophil function and limits inflammatory responses in healthy skin by restricting neutrophil recruitment. However, the CD200 pathway is reduced in psoriasis, resulting in a loss of immune control, and increased neutrophil recruitment in mouse models. In conclusion, we highlight a pathway that might be targeted to dampen inflammation in patients with psoriasis.