Induction of CCL3 and CCL4 protein expression by CLL cells after BCR engagement: anti-IgM dose-response. CLL cells were placed in culture medium supplemented with different concentrations of anti-IgM, as indicated on the vertical axis. CLL cells cultured with medium alone were used as controls. After 24 hours, supernatants were removed and assayed for CCL3 (A) and CCL4 (B) protein expression by ELISA. Displayed are the mean (± SD, n = 3) CCL3 and CCL4 concentrations, as indicated on the horizontal axis. Whereas anti-IgM induced a dose-dependent induction of CCL3 and CCL4, CLL cells cultured in medium alone did not express significant amounts of CCL3 and CCL4.