Background/Purpose: To analyze Stat1 and phosphorylated Stat1, the interleukin-6 (IL-6) receptor-Stat3 axis, and membrane bound tumor necrosis factor (mTNF) and TNF receptors 1 and 2 (CD120a and CD120b), in patients with SSc.

Methods: We prepared PBMC of 30 patients with SSc and 42 healthy individuals (HC). CRP, ESR, modified Rodnan skin score (mRSS)  and the EULAR activity score were recorded. For determining the percentages of CD120a, CD120b, CD126 and CD130 positive cells, PBMC were directly stained with PE-labelled or control antibodies. Ex vivo and after 15 minutes of incubation with or without recombinant human interferon-γ (IFN γ) or interleukin-6 (IL-6), PBMC were fixed with formaldehyde (2%), permeabilized with methanol (80%), and stained with PE-labelled control antibodies or antibodies to Stat1 or phosphorylated Stat1 (pStat1) or pStat3, respectively. Stained cells were immediately analyzed on a Becton Dickinson FACSCalibur fluorocytometer, independently gating for lymphocytes and monocytes. As a semiquantitative measure of (p)Stat contents, mean fluorescence intensity (mfi) was used. Data were expressed as mean±SD. 

Results: Both chains of the IL-6 receptor, CD126 and CD130, were expressed on decreased percentages of SSc lymphocytes (50.2±18.1% vs. 60.0±7.9%, p=0.0086, and 52.6±15.1% vs. 59.6±9.5%, p=0.0212, respectively). This translated into a diminished increase of pStat3 in SSc lymphocytes upon IL-6 stimulation (Δmfi 17.2±12.1 vs. 20.5±9.3, p=0.03, and 35.8±17.1 vs. 54.1±25.0, p=0.0129, respectively). In contrast, the increase in pStat1 upon IFNγ stimulation was more pronounced in SSc lymphocytes (Δmfi 10.5±11.2 vs. 4.8±3.7, p=0.0035), albeit their increased Stat1 contents (mfi 51.2±27.4 vs. 16.7±9.1, p < 0.0001) suggested ongoing activity of the IFN system in SSc. While the percentages of IL-6R positive monocytes were not significantly different from those of HC, their IL-6 induced  increase in pStat3 was nevertheless decreased (Δmfi 35.8±17.1 vs. 54.1±25.0, p=0.0129), and their IFNγ induced increase in pStat1 showed a trend towards being higher than normal (Δmfi 60.9±53.3 vs. 44.9±24.9, p=0.32). The percentage of mTNF positive lymphocytes was slightly decreased (2.3±0.8% vs. 3.2±1.8%, p = 0.0357), while mTNF monocytes were increased (68.1±30.0% vs. 24.3±24.4%, p<0.0001). CD120b was increased on both SSc lymphocytes (67.2±18.6 vs. 58.4±11.9, p=0.0017) and monocytes (93.4±9.0% vs. 75.4±19.9%, p < 0,001), whereas CD120a was increased on SSc monocytes (31.3±21.5% vs. 13.6±9.7%, p = 0.001) only. 

Conclusion: Our results suggest upregulation of the IFN-Stat1 and the IL-6-Stat3 axis in SSc, with a shift towards increased Stat1 phosphorylation. In addition, increased TNF and TNF receptors were found on SSc monocytes.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/increased-stat1-and-stat-1-phosphorylation-in-patients-with-systemic-sclerosis-ssc/