The presence of autoimmune thyroiditis in mixed cryoglobulinemia patients is associated with high levels of circulating interleukin-6, but not of tumor necrosis factor-alpha.

OBJECTIVES: To our knowledge, no study has evaluated serum levels of interleukin-6 (IL-6), together with tumour necrosis factor-alpha (TNF-α), in a large series of patients with 'mixed cryoglobulinemia and HCV chronic infection' (MC+HCV) in relation to the presence of autoimmune thyroiditis (AT). The aims of the study were to evaluate serum levels of IL-6 in MC+HCV patients and to correlate this parameter with the presence of AT and with circulating levels of TNF-α.METHODS: Serum IL-6 and TNF-α were assayed in 41 MC+HCV patients, in 41 MC+HCV patients with autoimmune thyroiditis (MC+AT), in 41 sex- and age-matched controls, and 20 AT patients.RESULTS: MC+HCV patients showed significantly (p<0.01; Mann-Whitney U-test) higher IL-6 (median 8.1ng/l, range 0.7-651) serum levels than controls (median 0.6ng/l, range 0.5-41), or AT (median 2.8ng/l, range 0.5-67). MC+AT showed significantly (p<0.01; Mann-Whitney U-test) higher mean IL-6 (median 15.8ng/l, range 0.5-781) than controls, AT and MC+HCV. Serum TNF-α levels were significantly higher in MC+HCV (median 9.9ng/l, range 1.5-283) or MC+AT (median 11.2ng/l, range 1.6-412) than in controls (median 1.0ng/l, range 0.6-6.4), or AT (median 1.7ng/l, range 0.6-11.8) (p<0.01, for each comparison).CONCLUSIONS: Our study demonstrates significantly higher serum levels of IL-6 and TNF-α in patients with MC+HCV and MC+AT compared to healthy controls. Furthermore, the study first shows a significant increase in circulating IL-6 observed in MC+AT patients with respect to MC+HCV. Future studies in larger patients' series will be needed to evaluate the relevance of serum IL-6 and TNF-α determination as clinico-prognostic markers of MC+HCV patients and its usefulness in the therapeutic approach to these patients.