In order to investigate the role of peripheral infiltrating macrophages (IMs) in chronic alcohol, we used a common model [20] of chronic alcohol consumption in mice (Fig. 1a). We measured the mRNA expression of the chemokine receptors Ccr2 and Ccr5 and the macrophage chemokine Ccl2, a ligand for CCR2, in the CNS. Alcohol significantly induced Ccl2, Ccr2, and Ccr5 expression compared with pair-fed controls in both the cerebellum and hippocampus (p < 0.05), but not in the cortex (Fig. 1b). To test if this upregulation of monocyte chemokines and receptors is associated with the infiltration of macrophages, we next isolated CNS immune cells from the total brain and examined the cells using flow cytometry. Peripheral IMs were defined by flow cytometry as CD11b+CD45hi cells to differentiate from CD11b+CD45lo microglia (Fig. 1c). CD11b+CD45hi IMs were significantly more abundant in alcohol-fed mice compared to pair-fed mice (6.2 ± 0.52% vs 12.03 ± 1.64%, p < 0.01) (Fig. 1d). These data suggested that peripheral immune cells indeed infiltrate into the CNS after alcohol feeding and, based on the differential expression of chemokine receptor and ligand, that they may be recruited to particular brain regions.
