Monocyte derived interleukin (IL)-23 is an important determinant of synovial IL-17A expression in rheumatoid arthritis.

OBJECTIVE: To demonstrate gene expression of interleukin (IL)-17A, IL-23, and IL-12 and to determine the proximity of IL-17A and IL-23 producing cells in rheumatoid synovial tissue. METHODS: Total RNA was isolated from 25 synovial membranes obtained from 20 patients with rheumatoid arthritis (RA). Quantitative real-time polymerase chain reaction was used to measure IL-17A, IL-12p35, IL-23p19, p40, and GAPDH expression. Immunohistochemistry was utilized to determine cell type and proximity of IL-17A, IL-12, and IL-23 in rheumatoid synovium. RESULTS: IL-17A was present in 13/25 synovia. IL-12p35 was present in all samples while IL-23p19 was present in 23/25. p40 was present in 23/25 samples. Of the 2 p40- samples both were IL-23p19 and IL-12p35 positive. Mean expression of IL-23p19 was significantly higher in the IL-17A+ versus IL-17A- synovia (0.10 +/- 0.02 ng vs 0.05 +/- 0.01 ng; p < 0.05). There was no difference in IL-12p35 expression between IL-17A+ and IL-17A- synovia (0.5 +/- 0.21 ng vs 0.38 +/- 0.24 ng; p = 0.2). All IL-17A+ cells were in the vicinity of IL-23+ cells. IL-12+ cells were both close to and removed from IL-17A+ cells. Only a proportion of CD3+T cells appeared to produce IL-17A. CONCLUSION: IL-17A gene expression occurs in only a subset of rheumatoid synovial membranes. IL-23 gene expression is higher in IL-17A+ versus IL-17A- membranes. In keeping with this, IL-17A+ and IL-23+ cells colocalize in synovial membranes. IL-17 is not an absolute requirement in RA but may be important in amplifying the inflammatory response. Anti-IL23 therapies may have a role in those patients with IL-17A expression.

Different T cell subsets in the nodule and synovial membrane: absence of interleukin-17A in rheumatoid nodules.

OBJECTIVE: To determine gene expression of the interleukin-17 (IL-17) family members (IL-17A-F) in rheumatoid subcutaneous nodules, and to assess the cytokines involved in regulating IL-17A expression. METHODS: Total RNA was isolated from 19 nodules obtained from 16 different patients with rheumatoid arthritis (RA). Reverse transcription-polymerase chain reaction (PCR) was used to screen for gene expression of the IL-17 subtypes (IL-17A-F) in all nodules. Quantitative real-time PCR was used to measure the expression of interferon-gamma (IFN gamma), IL-6, IL-23, IL-12, and transforming growth factor beta (TGFbeta), relative to GAPDH as control, in a subset of 10 nodules. RESULTS: IL-17A gene expression was present in only 1 of 19 nodules, IL-17B in 17 of 19 nodules, IL-17C in 18 of 19 nodules, IL-17D in 16 of 19 nodules, and IL-17E in 3 of 19 nodules. IL-17F was absent in all samples. Cytokines that stimulate IL-17A production (IL-6, IL-23) as well as those that inhibit IL-17A production (IL-12, IFN gamma, TGFbeta) were present in the majority of nodules. Quantitative real-time PCR showed a similar pattern of gene expression for the individual cytokines between the different nodules. The mean +/- SD expression of IL-6 relative to GAPDH was 2.28 +/- 2.2 ng, and that of TGFbeta was 2.96 +/- 1.14 ng. There was a lower relative expression of IL-23 (0.05 +/- 0.05 ng), while the expression of IFN gamma was 0.67 +/- 0.68 ng and that of IL-12 was 0.48 +/- 0.23 ng. CONCLUSION: IL-17 family members are varyingly expressed in rheumatoid nodules. The paucity of IL-17A in nodules suggests an important difference from that observed in the synovium. The expression of IL-23 below a critical threshold level seems the most likely explanation for the virtual absence of IL-17A. The presence of tissue destruction within the nodule despite the absence of IL-17A suggests that IL-17A may be an important amplifier rather than an absolute requirement for inflammation in RA.