CD44 and its role in inflammation and inflammatory diseases.

The cell adhesion molecule CD44 is expressed on the majority of immune cells and is responsible for mediating adhesion to the extracellular matrix glycosaminoglycan, hyaluronan. The binding of CD44 to hyaluronan is induced on T lymphocytes after activation by antigen and on monocytes after stimulation by inflammatory agents. Under inflammatory conditions, CD44 on endothelial cells presents hyaluronan to CD44 on activated T lymphocytes and mediates a rolling interaction under flow conditions. This rolling interaction together with chemokine signaling upregulates integrin-mediated adhesion, which induces cell arrest and leads to subsequent migration to the inflammatory site. Studies with monoclonal antibodies against CD44 in mouse models of chronic inflammatory disease showed reduced disease severity attributed to reduced leukocyte recruitment. More recent investigations, taking advantage of the availability of CD44 null mice, further established a role for CD44 in leukocyte recruitment to inflammatory sites. These studies also revealed a role for CD44 in limiting the inflammatory response and resolving inflammation in models of lung injury and hepatitis. Here we describe the contributions of CD44 and hyaluronan to an inflammatory response and discuss the role of CD44 in both promoting and resolving inflammation in various mouse models of inflammatory disease.