Adhesion of Activated T Lymphocytes to Vascular Smooth Muscle Cells and Dermal Fibroblasts is Mediated by β1- and β2-Integrins

Several studies during recent years have demonstrated the potential for vascular smooth muscle cells (SMC) and dermal fibroblasts to participate in immune interactions such as antigen presentation and alloreactivity. The molecular interactions mediating lymphocyte adhesion to these mesenchymal cells have, however, not previously been characterized in detail. In the present study we demonstrate ICAM-1 (CD54) expression by cultured human SMC and its up-regulation by IL-1, IFN-gamma, and bacterial lipopolysaccharide. Monoclonal antibodies were used to define the molecular interactions in the adhesion of 51Cr-labelled T lymphoblasts to adherent SMC and fibroblasts. ICAM-1 appeared to mediate adhesion of T lymphocytes by binding to the beta 2-integrin CD11a/CD18 (LFA-1) expressed by the lymphoblasts. We present evidence for the involvement of at least three different mechanisms in the adhesion of activated T lymphocytes to cultured fibroblasts. It was found that beta 2-integrin-mediated interaction could only account for less than half of the binding activity. The remaining adhesion was partly mediated by beta 1-integrins, presumably via VLA-5 since an anti-VLA-5 antibody and an RGD-containing peptide blocked adhesion to the same degree. However, antibodies to beta 1-, beta 2-, and beta 3-integrin subunits added together only inhibited adhesion by approximately 50%. The residual adhesion could be blocked by inhibition of cell metabolism and was increased by stimulation of the lymphocytes with phorbol ester, suggesting involvement of other, as yet undefined, adhesion molecules. The molecular interactions between lymphocytes and mesenchymal cells demonstrated in this study may have implications in several inflammatory conditions such as vasculitis, atherosclerosis, and connective tissue diseases.