Background In rheumatoid arthritis (RA) the production of rheumatoid factor (RF) by B-lymphocytes could depend on the action of different cytokines.
Objectives Aim of this study was to detect interleukin 13 (IL-13), a potent modulator of B-cell functions1, in sera of RA patients in order to investigate the relationship of this cytokine, with different class specific RFs.
Methods We studied 36 consecutive patients with RA, classified according to Arnett criteria and 20 healthy subjects matched for age and sex. In all patients, we evaluated the main clinical and laboratory parameters including the determination of IgM-RF, IgA-RF, IgG-RF and IL-13 by immunoenzimatic methods.
Results We found detectable levels of IL-13 (>1.56 pg/ml) in 86.1% of RA patients and in 40% of controls (p < 0.0006). The IL-13 serum levels were significantly (p < 0.00001) higher in patients with RA (mean/lower and upper 95% CI = 165.4/99.3–231.6 pg/ml) respect to the controls (mean/lower and upper 95% CI = 3.9/0.8–7.0 pg/ml). The serum levels of IL-13 correlated with those of IgM-RF (r = 0.591; p < 0.0001) and IgA-RF (r = 0.505; p < 0.002), while we didn’t find any relationship with IgG-RF, IgM, IgA and IgG levels. IgA-RF levels correlated with those of IgM-RF (r = 0.548; p < 0.0005) and IgG-RF (r = 0.543; p < 0.0006), while no relationship between IgM-RF and IgG-RF (r = 0.222; n.s.) was found. The comparison of patients with or without the different class specific RFs revealed that patients with IgM-RF had significantly (p < 0.018) higher levels of IL-13 respect to the patients without (mean/lower and upper 95% CI = 202.4/125.8–278.9 vs 12.6/2.2–22.9 pg/ml), while this finding was not observed for IgA-RF (mean/lower and upper 95% CI = 191.1/114.3–267.9 vs 59.3/-58.6–177.2 pg/ml) and IgG-RF(mean/lower and upper 95% CI = 239.4/48.6–430.2 vs 147.6/74.5–220.7 pg/ml). We didn’t find any relationship of serum IL-13 levels with clinical and other laboratory signs of disease activity.
Conclusion In conclusion our results show that IL-13 is involved in pathogenetic mechanism of RA, suggesting that IL-13 source could derive from an excessive joint or intravascular production by immune system. A relevant action of IL-13 seems to be related with a selective isotype production of IgM-RF.
Punnonen J, Aversa G, Cocks BG, McKenzie ANJ, Menon S, Zurawski G, De Waal Malefty R, De Vries JE. Interleukin 13 induces interleukin-4-indipendent IgG4 and IgE synthesis and CD23 expression by human B cells. Proc Natl Acad Sci USA 1993;90:3730–4
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