CD300a is an inhibitory immunoreceptor expressed in lymphoid and myeloid cells. This study evaluates whether CD300a plays a role in the control of joint inflammation in a model of Ag-induced arthritis (AIA) in mice. CD300a was found to be expressed mostly on neutrophils and its expression was enhanced on neutrophils that migrated to the inflamed synovial cavity. Joint inflammation, as characterized by neutrophil accumulation, was significantly greater in CD300a KO (CD300a−/−) mice subjected to AIA, as compared to WT mice. This was associated with joint dysfunction, as measured by lower mechanical nociception threshold. There was greater production of the chemokine CXCL1 and the cytokine IL-6 in joints of CD300a−/− mice. In vitro, Mϕs from CD300a−/− mice released higher concentrations of CXCL1 and IL-6 in response to LPS. Splenocytes from immunized CD300a−/− mice produced increased levels of IFN-γ and IL-17 and lower levels of IL-10 when challenged with Ag than cells from WT mice. Neutrophils lacking the CD300a gene had greater chemotactic activity in response to fMLP, CXCL1, and LTB4 than WT neutrophils. In conclusion, these results reveal that the absence of CD300a promotes exacerbation of inflammation in a model of Ag-induced arthritis, suggesting that CD300a is an important receptor for negatively controlling the inflammatory response in this model. Mechanistically, CD300a seems to regulate the activity of various immune cells types involved in the process, including neutrophils, Mϕs, and lymphocytes.
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