To assess whether interleukin 6 (IL-6) may influence autoantibody production, the correlation of rheumatoid factors (RF) and antitype II collagen antibodies with IL-6 was determined in children with juvenile rheumatoid arthritis (JRA).
IL-6 was measured by proliferation of the B-9 cell line or by ELISA: IgG, IgA, and IgM RF were measured by ELISA:
Plasma IL-6 levels were higher in patients with polyarticular JRA than controls. In serial studies, the presence of a greater number of RF isotypes and IgG antinative type II collagen antibodies correlated with higher IL-6 levels [1650 x divided by 3.4 vs 831 x divided by 4.4, p < 0.01 (geometric mean x divided by SD); and 1828 x divided by 5.9 vs 646 x divided by 4.1, p < 0.005, respectively]. The change in RF isotype expression most often involved IgG or IgA RF. In vitro IgG RF production increased in one and became detectable in another 2 cases upon the addition of IL-6 to B cell cultures.
Our results suggest that IL-6 may promote the production of IgG and IgA RF and IgG antinative type II collagen antibodies.