Significant higher-level C-C motif chemokine ligand 2/3 and chemotactic power in cerebral white matter than grey matter in rat and human.

Recent observations indicate that cerebral white matter (WM) exhibits a higher chemoattractant capability for immune cells. The C-C motif chemokine ligands 2 and 3 (CCL2, CCL3) are key chemokines for monocytes and T cells. However, tissue differential of these chemokines is unclear, although the higher CCL2/3 mRNA levels were found in rodent WM. It has been shown that more immune cells infiltrated to WM than to grey matter (GM) in multiple sclerosis (MS) and human/simian immunodeficiency virus (HIV/SIV)-infected brains. More nodular lesions have also been identified in the WM of patients with MS or HIV/SIV encephalitis. We hypothesize that higher levels of CCL2/3 in the WM may associate with neuropathogenesis. To test this hypothesis, we compared CCL2 and CCL3 peptide levels in WM and GM of rat and human, and found both were significantly higher in the WM. Next, we tested the effect of CCL2 on primary rat microglia migration and observed a dose-dependent migratory pattern. Then, we assessed effects of WM and GM homogenates on microglia chemotaxis and observed significant stronger effects of WM than GM in a concentration-dependent manner. The concentration-dependent pattern of tissue homogenates on chemotaxis was similar to the effect of CCL2. Finally, we found the chemoattractant effects of WM on microglia were significantly attenuated by addition of a CCL2 receptor blocker to culture medium and a neutralizing antibody against CCL3 functional motif in the WM homogenate. Taking together, these results suggest that CCL2/3 played significant roles in the microglia chemotaxis toward WM homogenate.