Fig. 4. CCL2/MCP-1 is the exclusive factor in the culture supernatants of U251MG-Nef_Bru cells capable of inducing chemotaxis of monocytic THP-1 cells. Cell culture supernatants from nef_Bru-expressing astrocytes (clones 4/4.1 or 4/4.2) or rCCL2/MCP-1 (25 ng/ml) were placed into the lower part of the chemotaxis unit and THP-1 cells in the upper part. At 45 minutes prior to the assay, supernatants and rCCL2/MCP-1-containing wells were incubated with anti-CCL2/MCP-1 antibodies or isotype-matched control antibodies as indicated. One representative experiment of four independent experiments is shown. Data represent mean ± s.e.m. of triplicates.