Figure 2.

Soluble domain 1 of PECAM is sufficient to block TEM. Freshly isolated PBMC were suspended to 2 × 10⁶/ml in medium M199 (M199), hec7 anti-PECAM mAb (20 μg/ml, 133 nM), or the indicated purified PECAM-IgG constructs at a final concentration of 100 nM. D1 IgG indicates a chimeric molecule comprised of domain 1 of human PECAM fused with the Ch2 + Ch3 domains of human IgG1. D1-6 IgM indicates a chimeric molecule comprised of full-length human PECAM fused with the Ch2 + Ch3 + Ch4 domains of human IgM. The cells were co-cultured for 1 h at 37°C to allow transendothelial migration, and the monolayers were then washed briefly in EGTA and DPBS before fixation and quantitation of transmigration as described previously (4, 8). The data are expressed as the mean ± standard error of five replicates for each sample. All chimeric proteins containing domain 1 of PECAM significantly blocked transmigration. Asterisks (*) indicate P <0.02. The results shown are from a representative experiment of seven such experiments.