Challenge with innate and protein antigens induces CCR7 expression by microglia in vitro and in vivo

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Abstract
Since activated microglia are able to phagocytose damaged cells and subsequently express major histocompatibility complex class II (MHC‐II) and co‐stimulatory proteins, they are considered to function as antigen presenting cells (APCs) in the central nervous system. The maturation and migratory potential of professional APCs is associated with the expression of chemokine receptor CCR7. We therefore investigated whether the immunological activation of microglia induces CCR7 expression. We here present that activation of cultured microglia by both the innate antigen lipopolysaccharide and protein antigen ovalbumin rapidly induces CCR7 expression, accompanied by increased MHC‐II expression. Moreover, it is shown that CCR7 expression in IBA‐1 positive cells is induced during the symptom onset and progression of experimental autoimmune encephalomyelitis, a rodent model for multiple sclerosis. These results suggest that microglia express CCR7 under specific inflammatory conditions, corroborating the idea that microglia develop into APCs with migratory potential toward lymphoid chemokines.