Binding of gp120 to CXCR4 does not involve activation of the ERK1/ERK2 MAP kinase pathway. CD4⁻/CXCR4⁺ Jurkat cells were preincubated in medium alone or in the presence of gp120 wt (10 μg/mL), gp120 ▵HX1 (10 μg/mL), SDF1 (25 nmol/L), the anti-CXCR4 12G5 MoAb (10 μg/mL), the anti-CD3 UCHT-1 MoAb (10 μg/mL), or the anti-CD4 ST4 MoAb (10 μg/mL) for 60 minutes on ice. Stimulations were then performed at 37°C for the indicated time periods before lysis. ERK1/ERK2 activation was assessed using a polyclonal anti-active MAP kinase Ab. The immunoblot was then stripped and reblotted with an anti-ERK2 MoAb.