Low-dose radiotherapy (LD-RT) and the modulation of iNOS expression in adjuvant-induced arthritis in rats

Purpose: Low‐dose radiotherapy (LD‐RT) of arthritic joints applied during the peak of the acute inflammatory response improves the clinical and histomorphological development of adjuvant arthritis. The study was undertaken to investigate the cellular composition of the inflammatory infiltrate and the expression of the pro‐inflammatory and anti‐inflammatory enzymes, inducible nitric oxide synthase (iNOS), cyclo‐oxygenase 2 (COX‐2) and haem‐oxygenase 1 (HO‐1), in response to LD‐RT.Materials and methods: Adjuvant arthritis in female Lewis rats was induced by intradermal injection of heat‐inactivated mycobacterium tuberculosis on day 0. Both arthritic hind paws were sham irradiated (group 1) or X‐irradiated with either 5×1.0 Gy (group 2) or 5×0.5 Gy (group 3) from days 15 to 19 after induction (15 animals/group). On days 21 (n=12 joints/group) and 30 (n=18 joints/group), cryostat sections were analysed histologically and immunohistologically after specific staining for macrophages, iNOS, COX‐2 and HO‐1.Result...