HLA-DR expression in the vascular lesion and circulating T lymphocytes of patients with giant cell arteritis.

Giant cell arteritis (GCA) is a vascular inflammatory disease characterized by accumulations of T lymphocytes and macrophages in the arterial wall. In order to characterize the immune response in GCA, we have analysed temporal artery biopsies using a double-staining immunofluorescence method and studied T lymphocytes in peripheral blood with a fluorescence-activated cell sorter (FACS). HLA-DR was expressed on 28% (range 16-42%) of all T lymphocytes in the wall of the inflamed temporal artery, but only on average on 6% of peripheral blood T lymphocytes, indicating a high degree of local T cell activation in the inflammatory lesion. The proportions of T lymphocytes, T helper/inducer and T suppressor/cytotoxic cells in the blood of GCA patients before treatment with prednisolone did not deviate from those in normal individuals, but there was a minor increase in T helper cells after initiation of steroid therapy. The number of T helper cells expressing HLA-DR antigen and IL-2 receptor was not altered after 6-10 days of treatment with prednisolone. We found no evidence of HLA-DR expression by arterial smooth muscle cells in the GCA lesions, suggesting that these cells do not serve as antigen-presenting cells in GCA.