Role of ICAM-1 and ICAM-2 and alternate CD11/CD18 ligands in neutrophil transendothelial migration

We evaluated the relative contribution of ICAM‐1 and ICAM‐2, known ligands on endothelium for LFA‐1 and Mac‐1, in spontaneous neutrophil (PMN) transendothelial migration (TEM) across IL‐1‐activated HUVEC monolayers or TEM induced by C5a or IL‐8 across unstimulated HUVEC grown on polycarbonate filters. Adhesion blocking mAb to ICAM‐1 [R6.5 F(ab)2] or ICAM‐2 [CBR IC2/2 F(ab)2] tended to inhibit TEM under each condition but, in general, inhibition was significant only with both ICAM‐1 and ICAM‐2 blockade. mAb to LFA‐1 partially inhibited migration to C5a or IL‐8 across unstimulated HUVEC and inhibition was not altered by additional treatment of HUVEC with mAbs to ICAM‐1 and ‐2. In contrast, with IL‐1 HUVEC, mAb to ICAM‐1 significantly inhibited this LFA‐1‐independent TEM. mAb to Mac‐1 alone partially inhibited TEM and, when combined with mAb to LFA‐1, migration was almost completely blocked with all TEM conditions tested. The contribution of alternate ligands for Mac‐1 in mediating Mac‐1‐dependent but ICAM‐1/‐2‐independent C5a‐induced TEM was examined using anti‐LFA‐1‐treated PMN and anti‐ICAM‐treated resting HUVEC. Addition of RGD peptides, fibronectin, fibrinogen, heparins, collagens alone or in combination, even to heparinase‐treated HUVEC, did not inhibit this Mac‐1‐mediated PMN TEM. The results indicate that: (1) LFA‐1 mediates PMN TEM primarily by interaction with ICAM‐1 and ICAM‐2; (2) ICAM‐2 may function in concert with ICAM‐1 in this role, especially on unstimulated endothelium, and (3) Mac‐1 on PMN also plays a major role in TEM and can utilize yet to be identified ligands distinct from ICAM‐1 or ‐2, especially on unstimulated endothelium. J. Leukoc. Biol. 65: 117–126; 1999.