The inflammatory reaction in giant cell arteritis: an immunohistochemical investigation.

OBJECTIVE: To assess the distribution of the inflammatory reaction in giant cell arteritis (GCA).
METHODS: Semiquantitative analysis on cryostat sections stained with monoclonal antibodies against inflammatory markers.
RESULTS: The inflammatory infiltration was strongest in the adventitia where it showed sharp demarcation along the outer border of the media. The endothelial immunopositivity for HLA-DR was strongest in adventitial microvessels. The immunopositivity for macrophages, B-cells, HLA-DR, ICAM-1 and IL-2 was significantly stronger in the outer than in the inner half of the intima.
CONCLUSION: The distribution of immunostainings and the crowding of cells seen at the outer media border indicates that the majority of the inflammatory cells enter the arterial wall from adventitial microvessels, migrate through the media and that the cell migration and the inflammatory activity focuses on the peripheral intima/internal elastic membrane.