A CD44 monoclonal antibody differentially regulates CD11a/CD18 binding to intercellular adhesion molecules CD54, CD102 and CD50

We have made a monoclonal anti‐CD44 antibody which is able to activate the leukocyte integrin CD11a/CD18. Activated T cells strongly aggregated, and the aggregation was shown to be intercellular adhesion molecule (ICAM)‐1 (CD54) and ICAM‐2 (CD102) dependent. Using purified ICAM coated on plastic, only binding to ICAM‐1 was increased by the CD44 antibody, whereas activation by phorbol ester increased binding to both ICAM‐1 and ICAM‐3. The binding to ICAM‐2 was not affected by either treatment. These findings show that the CD11a/CD18 integrin can be activated in a ligand‐specific manner by engagement of CD44.