Expression and function of ICAM-1 in the granulomatous inflammation of temporal arteritis

Abstract

Human intercellular adhesion molecule-1 (ICAM-1) plays an important role in lymphocyte activation and in a wide range of leucocyte effector functions. In order to study the role of ICAM-1 in the adhesion of different types of leucocytes, the human ICAM-1 gene was transfected into mouse L cells and ICAM-1 transfectants were used in adhesion assays. Lymphocytes and monocytes showed high levels of ICAM-1 mediated adhesion. The ability of cytokines, particularly IFN-γ, to induce ICAM-1 gene expression on haemopoietic and non-haemopoietic cells was demonstrated using northern blot analysis and flow cytometry. As cytokines play a crucial part in the development of the granulomatous inflammatory process immunohistochemistry was used to study the <u>in vivo</u> expression of ICAM-1 in temporal arteritis. Temporal arteries with early features of arteritis, as well as a histologically unaffected skip area, showed a regional induction of ICAM-1 expression on smooth muscle cells of the media. In more florid cases o( temporal arteritis, an additional induction of ICAM-1 expression was also seen on intimal myofibroblasts. Macrophages, epithelioid cells and multinucleated giant cells were also ICAM-1 positive. The pattern of expression of ICAM-1 in temporal arteritis suggests an important role in mediating the intercellular interactions which constitute the granulomatous response.