Analysis of cytokine expression in muscle in inflammatory myopathies, Duchenne dystrophy, and non-weak controls

We investigated the profiles of cytokine mRNA expression in muscle in 15 cases of inflammatory myopathy (IM) (5 each of polymyositis, inclusion body myositis, and dermatomyositis) and in 10 controls (5 of Duchenne dystrophy and 5 non-weak subjects). Expressions of the predominantly T cell-derived cytokines (interleukin (IL)-2, IL-4, IL-5, and interferon-gamma (IFN-gamma), of the predominantly macrophage-derived cytokines (IL-1, IL-6, and tumor necrosis factor-alpha (TNF-alpha)), as well as cytokines that can be of either T cell or macrophage origin (granulocyte-macrophage colony stimulating factor (GM-CSF) and transforming growth factor beta 1 (TGF-beta 1) and TGF-beta 2), were monitored by the reverse transcriptase-PCR method. The expression of T cell cytokine mRNAs for IL-2, IL-5, and IFN-gamma was generally weak or inconsistent. IL-4 mRNA expression was consistently moderate to strong in polymyositis but generally weak or absent in the other IMs. The expression of macrophage cytokine mRNAs for IL-1 alpha and IL-1 beta was weak or absent in all cases. Variable TNF-alpha mRNA expression was observed in 12 of 15 IM cases and faint or weak expression in 5 of 10 controls. Very strong GM-CSF expression was detected, but only on boosted PCR, in 12 of 15 cases of IM but in none of the controls. IL-6 was expressed only weakly or inconsistently. In contrast to the variable expression of several of the above mentioned cytokine mRNAs, all IM specimens strongly expressed TGF-beta 1 mRNA and 12 of 15 strongly expressed TGF-beta 2 mRNA. Thus, with the exception of IL-4 expression in polymyositis, a similar pattern of cytokine mRNA expression exists in the different types of IMs. Moreover, this pattern resembles that detected in non-weak and DD controls, although expression is generally weaker in the non-weak controls. The findings suggest that in IM muscle a sustained secretion of cytokines by T cells or of IL-1 by macrophages is not a prerequisite for operation of the immune effector response and that muscle may not be the site of ongoing sensitization.