FIGURE 4.

All three Ig folds of SIRPα ectodomain participate in dimerization on the cell surface. Membrane-bound SIRPα with full-length or truncated ectodomains was expressed transiently in CHO cells. A, flow cytometric analysis of surface expression. Each transfectant was probed with murine monoclonal anti-SIRPαD1 (SAF17.2; dashed line), anti-SIRPαD3 (SAF4.2; solid line), and an isotype control (dotted line). B, immunoblot analysis with rabbit antiserum against the full-length SIRPα ectodomain demonstrating that membrane-bound WTSIRPα, SIRPαD1-Myc₆, and SIRPαD2D3 dimerize on the cell surface after cross-linking with BS3. Results are representative of one of five independent experiments. C, control; X, cross-linked.