Adhesion molecules in cell–cell interactions

Introduction

Cell–cell interactions are a feature and function of all living cells. Examples include interactions of mobile cells such as ova and sperm and the solid coalescence of skin cells to form a watertight epidermis. Cell–cell interactions are of importance both in cell structure and cell function. Cell–cell interactions provide physical barriers (skin), boundaries (organ capsules) and tissue cohesion. They provide a mechanism of communication between cells (nervous tissue) and are the means of reproduction (the cell–cell interaction of ova and sperm). When these interactions occur in mobile cells, for example in the blood, they are the means of switching on, spreading or regulating fundamental processes such as inflammation and coagulation.

Many cell–cell interactions are mediated via cell adhesion molecules (CAMs). CAMs are surface membrane structures designed or adaptable to binding with similar structures, termed ligands, on other cells. Many CAMs have now been identified and their molecular structures have been elucidated. Based on structural homology, to date, six families of CAMs have been defined but there are a number of new adhesion molecules that are yet to be grouped.

The families so far known are the immunoglobulin family, the cadherin family, the integrin family, the selectins, the surface proteoglycan family and the sialomucin family. CAMs play an important role in signal transduction as well as mediating adhesion with other cells and matrix components. Most CAMs may also be found as soluble circulating proteins, and levels of these soluble CAMs have been found to be raised in inflammatory conditions.