Remission of collagen‐induced arthritis is associated with high levels of transforming growth factor‐β expression in the joint
Immunization of genetically susceptible strains of mice with heterologous type II collagen leads to the induction of a self‐limiting polyarthritis that begins to subside around 10 days after onset of clinical disease. The aims of this study were to compare pro‐ and anti‐inflammatory cytokine expression in the joints during the course of arthritis in order to identify cytokines involved in spontaneous remission of arthritis. DBA/1 mice were immunized with type II collagen and an immunohistochemical analysis of expression of proinflammatory cytokines [tumour necrosis factor (TNF)‐α, interleukin (IL)‐1β and IL‐6] and anti‐inflammatory cytokines [IL‐10, IL‐1ra, transforming growth factor (TGF)‐β1, TGF‐β2 and TGF‐β3] in joints was carried out over the course of the disease. Both pro‐ and anti‐inflammatory cytokines were found to be expressed in early arthritis. However, around 10 days after onset of arthritis, the level of expression of proinflammatory cytokines declined while the level of expression of anti‐inflammatory cytokines, particularly TGF‐β1 and TGF‐β2, increased. Surprisingly, TNF‐α continued to be expressed at low levels during the period of disease remission (30 days after onset). Blockade of TNF‐α during the period of disease remission had no effect on TGF‐β expression. This study confirms that the level of inflammation in arthritis correlates strongly with the balance of pro‐ and anti‐inflammatory cytokine expression in the joints. Of the anti‐inflammatory cytokines studied, TGF‐β1 and TGF‐β2 predominate during the time of disease remission, suggesting that these cytokines are involved in regulating disease activity.