Functional analysis of α1β1 integrin in human natural killer cells

AbstractUpon activation with interleukin (IL)‐2 human natural killer (NK) cells acquire on their surface the α1β1 and α2β1 integrins and down‐regulate the expression of α6β1. By employing α1β1‐specific monoclonal antibody (mAb) HP‐2B6, characterized in our laboratory, we examined the functional role of the α1β1 integrin in NK cells. Treatment with HP‐2B6 mAb partially interfered with attachment of cultured NK cells to type I collagen, and combined with an anti‐α2β1 (TEA 1/41) mAb, it completely abrogated cell adhesion to this extracelular matrix protein. In contrast, NK cell attachment to laminin was completely blocked by the anti‐β1 LIA 1/2 mAb, but was unaffected by α1 and α2‐specific mAb; as α3β1 and α6β1 were undetectable, the data indicate that the α1β1 integrin binding sites for type I collagen and laminin are different. Incubation with anti‐α1 HP‐2B6 or its F(ab')2 fragments specifically induced a rapid homotypic aggregation of NK cells that was dependent on active metabolism, an intact cytoskeleton and the presence of divalent cations (Ca2+ and Mg2+); homotypic cell adhesion was selectively blocked by anti‐CD18, CD11a or CD54 mAb. In addition, stimulation of cultured NK cells with the anti‐α1 HP‐2B6 enhanced TNF‐α production and induced tyrosine phosphorylation of a 110‐kDa protein. Pretreatment with specific inhibitors of protein tyrosine kinase (PTK) activity (tyrphostin 25 and herbimycin A) completely abrogated the functional effects induced by the anti‐α1 HP‐2B6 mAb. Our data show that ligation of the α1β1 integrin positively modulates IL‐2‐activated NK cell function via a PTK‐dependent pathway.