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Human peripheral monocytes have been categorized into three subsets based on differential expression levels of CD14 and CD16. However, the factors that influence the distribution of monocyte subsets and the roles which each subset plays in autoimmunity are not well studied. Here we show that circulating monocytes from patients with autoimmune uveitis exhibit a skewed phenotype towards intermediate CD14++CD16+ cells, and that this is associated with glucocorticoid therapy. We further demonstrate that CD14++CD16+ monocytes from patients and healthy control donors share a similar cell surface marker and gene expression profile. Comparison of the effects of intermediate CD14++CD16+ monocytes with classical CD14++CD16− and non-classical CD14+CD16++ monocytes revealed that the intermediate CD14++CD16+ subset had an attenuated capacity to promote both naïve CD4+ T cell proliferation and polarization into a Th1 phenotype, and memory CD4+ T cell proliferation and IL-17 expression. Furthermore, CD14++CD16+ cells inhibit CD4+ T cell proliferation induced by other monocyte subsets and enhance CD4+ T regulatory cell IL-10 expression. These data demonstrate the impact of glucocorticoids on monocyte phenotype in the context of autoimmune disease and the differential effects of monocyte subsets on effector T cell responses.

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