Background/Purpose
Interleukin 6 (IL 6) is postulated to play a role in the pathogenesis of Giant Cell Arteritis. Several studies have demonstrated increased circulating IL 6 levels and upregulation of IL 6 in the temporal arteries of patients with GCA.
Multiple recent uncontrolled reports have noted improvements in clinical and laboratory parameters in patients with GCA treated with tocilizumab, an IL 6 receptor antagonist. However, persistent vascular inflammation has been reported in some cases.
The aim of this study was to examine the ability of IL 6 to induce pro- inflammatory mediators in ex -vivo temporal artery explant cultures.
Methods:
28 patients meeting 1990 ACR classification criteria for GCA were prospectively recruited. To directly examine the effects of IL 6 on pro-inflammatory mediators in GCA, ex-vivo temporal artery explant models were established.
Temporal artery explants were cultured in the presence or absence of recombinant human IL 6 (20 or 40 ng/ml) for 24 hours.
IL 6 mediates its effects through gp130 and the IL6 receptor. While gp130 is ubiquitous, the IL 6 receptor is limited to certain cells and therefore cells lacking the IL 6 receptor are unresponsive to the direct effects of IL 6. To overcome this, explants were co-cultured with rIL 6 and its soluble receptor (sIL6R).
Explant supernatants were harvested after 24 hours and assayed for IFNg, TNF, SAA, IL1b, IL 17, IL 8 and VEGF by ELISA. Of the cultured biopsies, 4 were snap frozen, protein was extracted and pSTAT3 expression assessed by Western Blot.
Graphpad Prism Ver 6.0d was used for statistical analysis. Results are presented as the mean +/- SEM in pg/ml/mg of biopsy weight.
Results
Stimulation with IL 6 did not induce any of the pro -inflammatory mediators assayed. No differences were observed in the explants cultured in the presence or absence of the sIL6R or between those with a positive (n=11) or negative (n=17) temporal artery biopsy. Increasing the concentration of IL 6 to 40 ng/ml did not alter our findings.
Mean values of VEGF did increase following treatment with IL6, even in the absence of sIL6R in keeping with the known ability of IL 6 to promote angiogenesis.
Western Blot analysis revealed increased expression of pSTAT3 in response to the combination of IL6+sIL6R, but not IL 6 alone, suggesting that the addition of the sIL6R is necessary to induce signal transduction.
|
|
Basal:
|
Stimulated: IL6 (20 ng/ml) |
p value: Wilcoxon signed-rank test |
|
INFg |
27.13 +/-8.6
|
36.10 +/- 12.8 |
0.148 |
|
TNF |
5.93 +/- 1.9
|
7.39 +/- 2.6 |
0.460 |
|
IL1b |
2.45 +/- 0.6
|
2.52 +/- 0.85 |
0.945 |
|
IL 17 |
11.08 +/- 4.9
|
16.92 +/- 8.20 |
0.843 |
|
IL 8 |
16, 563 +/- 5458
|
19,118 +/- 6698 |
0.277 |
|
SAA * ng/ml/mg |
10.42 +/- 4.31
|
7.45 +/- 2.54 |
0.625 |
|
VEGF |
7.74 +/- 3.45
|
107.3 +/- 78.44 |
0.062 |
Conclusion
IL6 stimulation of temporal artery explants from patients with GCA, at concentrations sufficient to activate STAT3 and up regulate VEGF, did not result in increased expression of key pro-inflammatory mediators. This data argues against a central role for IL6 in driving vascular inflammation in GCA and raises the hypothesis that anti-IL6 based therapeutic strategies may have a lesser impact on vascular inflammation than on the systemic inflammatory syndrome in patients with GCA.
Disclosure:
L. O’Neill,
None;
J. McCormick,
None;
W. Gao,
None;
C. Murphy,
None;
G. M. McCarthy,
None;
D. J. Veale,
None;
U. Fearon,
None;
E. S. Molloy,
None.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/interleukin-6-does-not-upregulate-pro-inflammatory-cytokine-expression-in-an-ex-vivo-model-of-giant-cell-arteritis/