Blocking antibodies to CCR5 decrease CCL3-induced chemotaxis in alveolar macrophages, but not fresh monocytes. Freshly isolated monocytes and alveolar macrophages (4.5 × 104/condition) were pre-incubated with 1 μg/ml CCR5 blocking antibodies and subjected to a migration assay using CCL3 (1–100 ng/ml) as the chemoattractant. The addition of anti-CCR5 antibodies did not significantly alter monocyte chemotaxis (left panel) at any concentration of CCL3 compared to the IgG control (p > 0.05 at all concentrations). In contrast, the addition of anti-CCR5 antibodies decreased CCL3-induced alveolar macrophage chemotaxis (right panel) at all tested concentrations of CCL3 (**p < 0.001). Results represent mean ± SEM for three independent studies.