Binding of gp120 to freshly isolated human CD4⁺ T lymphocytes does not result in MAPK activation.

(A) CD4⁺ lymphocytes were purified by negative selection and were immediately stained with PE-conjugated anti-CXCR4 or anti-CD4 mAbs. CD4 and CXCR4 staining profiles are shown, and the filled histogram depicts staining with an isotype-matched control mAb. (B) The CD4⁺ lymphocytes isolated as described in (A) were immediately stimulated with either gp120, SDF-1, an αCD3 mAb, or an αCD4 mAb. Protein lysates from 1 × 10⁶ cells were resolved on an SDS gel and analyzed as described in the legend to Figure 1. The positions of phosphorylated Erk1 and Erk2 are noted. Blots were reprobed with an αZAP-70 mAb to assure that expression of a T-cell–specific protein was equivalent in each lane. Data are representative of results obtained in 4 independent experiments with CD4⁺ lymphocytes from 4 different donors.