Integrins: cell adhesives and modulators of cell function.

Integrins encompass a family of cell-surface molecules which play a crucial role in cell-cell and cell-extracellular matrix interaction. Of these heterodimeric transmembrane glycoproteins (consisting of an alpha and beta chain) as yet at least 20 different types have been described, all with a different pattern of reactivity with extracellular matrix components. In this review the cell and tissue distribution of the integrins is discussed, with special emphasis on immunohistochemical localization of the beta 1 integrins and the alpha 6 beta 4 integrin. The beta 1 integrins comprise a subfamily in which eight alpha chains combine with one beta (the beta 1) chain. The alpha 2 beta 1, alpha 3 beta 1 and alpha 6 beta 1 and the alpha 6 beta 4 integrins are expressed on a wide variety of epithelia on the basolateral surface or exclusively on the basal surface facing the basement membrane (e.g. alpha 6 beta 1 and alpha 6 beta 4). Leucocyte integrins, which share a common beta 2 chain, occur almost exclusively on white blood cells and their precursors. The vitronectin receptors, which share a common alpha v chain, occur in a wide variety of cell types. Integrins play a major role in the interaction of the cell with the extracellular matrix in order to create and maintain tissue architecture. It has become clear, however, that through integrin-ligand interaction cell function is also modulated. Furthermore, in pathological conditions integrins play a role of some significance. Integrins mediate leucocyte traffic in developing inflammatory processes and function in neoplastic growth when it comes to invasion and metastasis.