Triggering through CD16 or phorbol esters enhances adhesion of NK cells to laminin via very late antigen 6

The mechanisms involved in the regulation of activationdependent integrin receptor functions are still unclear. Increased avidity for counter ligands as a result of cell activation is a behavior common to many integrin receptors (7) . Nevertheless, the molecular basis of enhanced integrin function is largely unknown . Quantitative changes in cell surface integrin expression appear not to be particularly relevant, as indicated by the failure to demonstrate increased receptor levels accompanying increased binding in many different systems (10, 11, 22) and also in our study. Therefore qualitative changes, i.e., posttranslational modifications of either a and/or /3 integrin subunits, as well as of other integrin-associated molecules such as cytoskeleton components, are likely to occur. Among the possible posttranslational modifications, phosphorylation appears to be a good candidate as a mechanism regulating integrin receptor functions because of its reversible nature. Cytoplasmic domains of a and a subunits have been shown to be substrates of kinase activities . Neverthe-less, changes in integrin avidity are not always associated with their phosphorylation, and in some cases they appear to be induced instead by nonproteic components (23, 24) .