Antigen presentation by the endothelium: a green light for antigen-specific T cell trafficking?

The functional consequences of recognition of antigen displayed by the endothelium during T cell extravasation in the development of an immune response have been a matter of debate for a long time. Most investigations have focused on the induction of proliferative responses and cytokine production by T cells. In parallel, endothelial cells have been shown to express costimulatory molecules with positive and negative regulatory effects on T cell responses. Recent studies have provided an alternative view of the antigen presenting cell function of endothelial cells, suggesting that cognate recognition of the endothelium by trafficking T cells is a key event in selecting the migration of antigen-specific lymphocytes into the site of inflammation.