Characterization of intercellular adhesion molecule-1 (ICAM-1)-augmented degranulation by cytotoxic T cells. ICAM-1 and anti-CD3 must be co-localized for optimal adhesion and stimulation

Purified intercellular adhesion molecule-1 (ICAM-1), a ligand of the LFA-1, was used to analyze the contribution of ICAM-1 to the activation of CTL. ICAM-1 facilitates degranulation when co-immobilized with substimulatory amounts of anti-CD3. This facilitated response is most likely mediated through LFA-1, since Abs to this molecule significantly inhibit the response, Interestingly, when ICAM-1 and anti-CD3 are immobilized on separate beads and presented to the CTL, no ICAM-1-enhanced degranulation is observed. The ICAM-1 and anti-CD3 must be immobilized on the same surface to augment the response, suggesting that ICAM-1 either does not transmit signals into the cell or it transmits a very localized signal, since the ICAM-1 and anti-CD3 must be juxtaposed. Consistent with this finding, we demonstrate that ICAM-1 does not induce tyrosine phosphorylation or a Ca(2+)-flux in the CTL clone, but does potentiate these responses when co-immobilized with substimulatory anti-CD3. Finally ICAM-1 and anti-CD3 must be immobilized on the same bead for stable adhesion of CTL to ICAM-1. When ICAM-1 and anti-CD3 are immobilized on separate beads, there is only a transient, low level of adhesion to the ICAM-1 beads. Taken together, these results suggest that LFA-1 is acting principally as an adhesion molecule, with respect to ICAM-1, in CTL and that this adhesion is regulated through the TCR complex.