CCL2 recruits T cells into the brain in a CCR2-independent manner.

CCL2 is a chemokine that can be induced during neuroinflammation to recruit immune cells, but its role in the central nervous system (CNS) is unclear. Our aim was to better understand its role. We induced CCL2 in CNS of naive CCL2-deficient mice using intrathecally administered replication-defective adenovirus and examined cell infiltration by flow cytometry. CCL2 expression induced pronounced and unexpected recruitment of regulatory and IFNγ-producing T cells to CNS from blood, possibly related to defective egress of monocytes from CCL2-deficient bone marrow. Infiltration also occurred in mice lacking CCR2, a receptor for CCL2. Expression of another receptor for CCL2, CCR4, and CXCR3, a receptor for CXCL10, which was also induced, were both increased in CCL2-treated CNS. CCR4 was expressed by neurons and astrocytes as well as CD4 T cells, and CXCR3 was expressed by CD4 and CD8 T cells. Chemokine-recruited T cells did not lead to CNS pathology. Our findings show a role for CCL2 in recruitment of CD4 T cells to the CNS and show that redundancy among chemokine receptors ensures optimal response.