The leucocyte β2 (CD18) integrins: the structure, functional regulation and signalling properties

Leucocytes are highly motile cells. Their ability to migrate into tissues and organs is dependent on cell adhesion molecules. The integrins are a family of heterodimeric transmembrane cell adhesion molecules that are also signalling receptors. They are involved in many biological processes, including the development of metazoans, immunity, haemostasis, wound healing and cell survival, proliferation and differentiation. The leucocyte-restricted beta 2 integrins comprise four members, namely alpha L beta 2, alpha M beta 2, alpha X beta 2 and alpha D beta 2, which are required for a functional immune system. In this paper, the structure, functional regulation and signalling properties of these integrins are reviewed.