[Cell adhesion molecules and the immune system]

Cellular interactions are controlled by complex mechanisms which come into play at the receptors on the cell surface (adhesion molecules: selectins, integrins, superfamily of immunoglobulins), the soluble cell mediators (cytokines) and the components of the tissue matrix (fibronectin, collagen, etc.). Disturbance of one of these systems may induce a pathological condition. The physiological state of the individual therefore depends on the balance of all these components. In the development of inflammation, adhesion molecules play an essential role in the localisation of the inflammatory response. At this level, the vascular endothelium, a governing barrier for the exchanges between blood and the tissues, plays an active part in regulation of the transcapillary permeability, control of proliferation of haematopoietic cells and the phases of the inflammatory response. After they have marginated, the active cells migrate by diapedesis towards the site of inflammation by creation of chemotactic signals as the adhesion between the cells is insufficient to induce their migration. The adherence phenomena depend on a process that is strictly controlled by the cytokines and enable intervention of cell-cell reactions and cell-protein recognition of the extra-cellular matrix. Cytokines play a key role in control of the expression and/or avidity of membrane receptors for ligand(s). An appropriate and rapid response of the circulating cells depends on coordination of the train of events that regulate the functional expression of the adhesion molecules. Use of specific antibodies that prevent cell adherence opens very important therapeutic possibilities because a single blockage of cell adhesion can have an immediate direct impact on development of the inflammatory response.