Deletion of the Complement Anaphylatoxin C3a Receptor Attenuates, Whereas Ectopic Expression of C3a in the Brain Exacerbates, Experimental Autoimmune Encephalomyelitis

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Abstract
The C3aR is expressed throughout the CNS and is increased in expression on glial cells during CNS inflammation. However, the role that C3a and the C3aR play in chronic inflammation, such as in the demyelinating disease experimental autoimmune encephalomyelitis (EAE), remains unclear. We show in this study that deletion of the C3aR is protective in myelin oligodendrocyte glycoprotein-induced EAE in C57BL/6 mice. C3aR-deficient (C3aR−/−) mice had a significantly attenuated course of EAE compared with control mice during the chronic phase of the disease. Immunohistochemical analysis demonstrated modestly reduced macrophage and T cell infiltration in the spinal cords of C3aR−/− mice. To examine the role of C3a in EAE, we developed a transgenic mouse that expresses C3a exclusively in the CNS using the glial fibrillary acidic protein (GFAP) promoter. We observed that C3a/GFAP mice had exacerbated EAE during the chronic phase of the disease, with significant mortality compared with nontransgenic littermates. C3a/GFAP mice had massive meningeal and perivascular infiltration of macrophages and CD4+ T cells. These studies indicate that C3a may contribute to the pathogenesis of demyelinating disease by directly or indirectly chemoattracting encephalitogenic cells to the CNS.