Expression of cell cycle proteins. Microglia were incubated for 24 h with fresh media (control), LPS 0.1 μg/ml, MCP-1 50 ng/ml, or a combination of LPS and MCP-1 at the indicated concentrations. RNA was isolated and cyclin D1 (A), CDK4 (B) and PCNA (C) mRNA levels determined by RT-PCR. Data are expressed as percentage of control values (set to 100%); **p < 0.001 versus control, *p < 0.005 versus control, p < 0.005 versus LPS. Data are means ± SE of n = 6 replicates per group.