Serum levels of interferon alpha do not correlate with disease activity in patients with dermatomyositis/polymyositis
Abstract
Recent studies show an important role of type I interferon (IFN) in the pathogenesis Idiopathic inflammatory myopathies. In order to investigate the relationship of soluble IFNalpha serum levels with clinical and laboratory characteristics we analysed serum samples of 43 patients with dermatomyositis (DM) or polymyositis (PM).
Patients were selected with the preference for those who were anti-Jo-1 positive, and had muscle MRI performed. Significantly lower levels of IFNalpha were found in patients with myositis in comparison with control groups.
There were no significant differences in IFNalpha levels between patients with PM and those with DM. IFNalpha levels were significantly higher in patients who were anti-Jo-1 positive (n=26; median 117.8 pg/ml, range 70–378) in comparison to patients who were anti-Jo-1 negative (n=17; median 93.4 pg/ml, range 0–199) (p=0.05), which is in accordance with described IFNalpha-inducing capacity of anti-Jo-1 positive serum samples.
A statistically significant negative correlation was found between IFNalpha and the intensity of MRI signal. None of the clinical or laboratory parameters of activity, showed any correlation with IFNalpha levels, with the exception of the tendency to higher IFNalpha levels (p=0.064) in the presence of interstitial lung disease detected by high- resolution CT (n=22) or chest x-ray (n=4).
Serum levels of IFNalpha do not seem to be an indicator of clinical activity, rather the opposite; the lower the serum level the more severe the muscle oedema, as demonstrated by the intensity parameter on MRI. Hypothetically, IFNalpha produced locally could be also locally consumed and not released into the circulation.
Alternatively, other type I IFNs and not the IFNalpha may be responsible for the type I IFN signature that is characteristic for many patients with DM and PM.