Lyn kinase activity is up-regulated by gp120 and MIP-1β in macrophages. MDMs were stimulated with (A,C) R5 gp120 (40 nM) or (B) MIP-1β (25 nM). At the indicated time points cell lysates were immunoprecipitated with antibodies specific for Lyn or Hck kinases and subjected to in vitro kinase assay (KA; top rows). In parallel, retained cell lysates (25 μg) were subjected to Western blotting for total Lyn or Hck protein (WB; bottom rows).