Cell‐type‐specific expression of p53 and p21 in giant cell arteritis

The aim of the present study was to investigate the expression of TP53 (p53) and CDKN1A (CIP1; p21) in the arterial wall in giant cell arteritis (GCA). Cross‐sections from 18 temporal artery biopsies displaying GCA and 8 control arteries were double‐stained with monoclonal antibody directed at p53 or p21 on the one hand and alpha‐smooth muscle actin, CD68 (macrophage) or CD3 (T‐cell) on the other. Nuclear p53 was expressed in CD68‐positive cells and smooth muscle cells in 16 of the 18 inflamed arteries. P21‐positive nuclei were found in CD68‐positive cells in 14 biopsies and in smooth muscle cells in all the specimens. All p53‐positive giant cells also contained p21‐positive nuclei. In the giant cells, immunopositive nuclei were mixed with negative ones. CD3‐positive T‐cells did not express p53 or p21. Only one p53‐positive smooth muscle cell nucleus was found in the non‐GCA controls and, compared with GCA, p21 expression was noted in few smooth muscle nuclei. The presence of p53 and p21 in the same types of cell in GCA indicates that the former protein is functional; p21 expression is induced by wild‐type, functional p53 but not by its mutant form. The current observations suggest cellular stress in GCA, the nature of which requires further investigation.