To determine whether plasma interleukin-6 (IL-6) and G/C base exchange polymorphism at position -174 of the IL6 gene have an effect on the clinical manifestations of primary Sjögren's syndrome (pSS).
Levels of circulating IL-6 protein and polymorphism of the IL6 gene were analysed in 66 patients with pSS and in 400 healthy subjects. These data were studied in relation to clinical data on the pSS patients.
Plasma IL-6 was elevated in pSS patients compared with healthy controls. pSS patients with coeliac disease, pulmonary fibrosis or alveolitis or peripheral nervous system symptoms had significantly higher IL-6 levels than patients without these manifestations. IL-6 levels increased in parallel with the histological grade of minor salivary gland biopsy and the number of pSS criteria fulfilled. IL6 allele frequencies were similar in patients and normal subjects. Plasma IL-6 levels were regulated by the IL6 genotype in pSS patients.
The G/C polymorphism of the IL6 gene does not predispose patients to pSS, but the circulating IL-6 concentration is related to specific manifestations of the disease and the levels of IL-6 are regulated by the IL6 promoter polymorphism in pSS.