Phosphorylation of the β‐subunit of CD11/CD18 integrins by protein kinase C correlates with leukocyte adhesion

Adhesion of activated leukocytes to cells is of critical functional importance. The adhesion is known to be mediated mainly by the CD11/CD18 integrins, also known as leukocytic cell adhesion molecules, or Leu‐CAM. We have now studied the phosphorylation of Leu‐CAM by protein kinase C and the correlation of phosphorylation with the generation of the adhesive phenotype among human peripheral blood mononuclear leukocytes during cell activation. We here show that a good correlation exists between the phosphorylation of the β subunit of Leu‐CAM (CD18), and the extent of cell‐to‐cell adhesion. The phosphorylated CD18 subunit was associated with both CD11a and CD11b. Purified protein kinase C was able to phosphorylate the β subunit of isolated Leu‐CAM in vitro. The phosphorylation occurred mainly on serine residues.