Lyn inhibition blocks CCR5-mediated ERK-1/2 activation. MDMs were pretreated for 2 hours with the Lyn kinase peptide inhibitor KRX-123.302 (0.1 μM) or the negative control peptide KRX-107.110 (0.1 μM). Cultures were then stimulated for 15 minutes with (A) MIP-1β (25 nM) or (B) R5 gp120, in the continued presence or absence of peptides. Cell lysates were subjected to ERK-1/2 Western blot using phospho-specific antibodies (P-ERK). Membranes were then stripped and reblotted with total ERK-1/2 antibodies (T-ERK).