CCR5 mediates ERK-1/2 phosphorylation. (A) MDMs from wild-type or CCR5Δ32 homozygous donors were stimulated for 15 minutes with R5 gp120 (40 nM) or MIP-1β (25 nM). Cell lysates were then subjected to Western blot using antibodies specific for phosphorylated (P-ERK) or total ERK-1/2 protein (T-ERK). (B) MDMs were pretreated for 1 hour with the CCR5 antagonist M657 (1 μM), stimulated in the continued presence of the inhibitor with R5 gp120 or MIP-1β, and analyzed by Western blot for phosphorylated or total forms of ERK-1/2.