Adhesion molecules are transmembrane or membrane-linked glycoproteins cell surface proteins that mediate the interaction between cells, or between cells and the extracellular matrix (ECM). There are five types of adhesion molecules: integrins, cadherins, selectins, members of the immunoglobulin superfamily (IgSF) and others such as mucins.
Integrins typically bind to the extracellular matrix, while cadherins, selectins and IgSF members are associated with cell-cell adhesion. Cadherins (calcium-dependent adherent proteins) are associated with cell-cell adhesive bonds in tissues. Cadherins exist as classical cadherins (type I and II), protocadherins and atypical cadherins. Selectins are further divided into P-, E- and L-selectins and are associated with the initial stage of the rolling cell adhesion cascade. The IgSF is one of the largest and most diverse protein families, including major histocompatibility complex (MHC) class I and II molecules and proteins of the T cell receptor (TCR) complex.
Cell–cell and cell–substrate adhesion is an important morphogenetic factor in multicellular organisms. Adhesive mechanisms maintain tissue structure in animals and allow the generation of force and movement. Cell adhesion is also an integrated component of the response of the immune system and wound healing, and is important in cancer development.