ICAM-2 mediates angiogenesis in vivo: Matrigel plug assay. Matrigel plugs were generated by subcutaneous injection of Matrigel; the plugs were removed 7 days later and processed for H&E staining. (A) In samples from WT mice (top), formation of vascular structures within the plugs is accompanied by erythrocyte and leukocyte infiltration. In samples from ICAM-2^–/– mice (bottom) a significant reduction in vascular structures and cellular infiltration within the plugs was observed. Arrowheads show blood vessels. Scale bar equals 100 μm. Images were acquired as in Figure 1A. (B) The vascular lumen area was measured using Image ProPlus software. The average vessel-containing area was calculated from 5 representative 100 × fields of 3 representative serial sections of each plug and is shown as the percentage of area occupied by blood vessel (BV)/100 × field. Compared with WT mice, a 50% reduction in vessel-containing areas were observed in samples from ICAM-2^–/– mice. Data represent 1 of 2 independent experiments; 5 to 6 mice per group were used in each experiment. Error bars indicate mean ± SEM. **P < .01, unpaired t test.