Expression of IFN-gamma-inducible chemokines in inclusion body myositis.

Because IFN-gamma-inducible chemokines, Mig (CXCL9), IP-10 (CXCL10), I-TAC (CXCL11) and their receptor, CXCR3, are critical molecules in T cell trafficking and generation of effector T cells, we examined their expression in the muscle biopsies of patients with sporadic inclusion body myositis (s-IBM) and disease controls. The functional role of these molecules was also studied by examining the effect and time kinetics of IFN-gamma in inducing Mig and IP-10 expression in human myotubes in vitro. We found significantly high levels of Mig and IP-10 mRNA expression in s-IBM muscles compared to controls. IFN-gamma upregulated the mRNA expression of Mig and IP-10 by human myotubes in a dose-dependent manner. By double-label immunohistochemistry, Mig was expressed on a subset of CD8(+) cells and the areas of the muscle fiber in contact or contiguous to the T cells; CXCR3 was expressed only on a subset of the autoinvasive CD8(+) T cells but not the myofibers. IP-10 and I-TAC were not detected by immunocytochemistry. The findings indicate that in s-IBM, IFN-gamma is involved in the upregulation and in situ production of proinflammatory chemokines, which, in turn, participate in the recruitment of activated T cells and contribute to the self-sustaining nature of endomysial inflammation.