Figure 5.

Displacement of ¹²⁵I-labelled stromal cell-derived factor-1α (SDF-1α) binding to freshly isolated (a) and interleukin (IL)-4-stimulated (b) CD4⁺ T lymphocytes by unlabelled SDF-1α and a specific monoclonal antibody (mAb) (12G5) to CXC chemokine receptor 4 (CXCR4). CD4⁺ T lymphocytes (5 × 10⁵/ml) were incubated in phosphate-buffered saline (PBS) with ¹²⁵I-labelled SDF-1α (0·2 nm) in the absence (indicated as 1) and presence (indicated as 2) of unlabelled SDF-1α (1 µm), or with CXCR4 mAb (500 nm) (indicated as 3), at 4° for 1 hr. The plots of Scatchard analysis on binding characteristics for SDF-1α are shown on freshly isolated (c) and IL-4-stimulated (d) CD4⁺ T lymphocytes. The dissociation constant (K_d) for each is given in the Results. The results shown in each plot are representative of those found in two similar experiments.