Background/Purpose:

Clinical diversity in systemic sclerosis (SSc) is likely to reflect multifaceted pathogenesis and the effect of key growth factors or cytokines operating within a disease-specific microenvironment. Dermal interstial fluid sampling offers the potential to examine local biological mechanisms and define protein expression within lesional tissue.  We propose multiplex cytokine analysis could be a pragmatic method to define the inflammatory and immune activity in the lesions of SSc patients.

Methods:

Interstitial fluid samples from forearm skin of patients (n=25; DcSSc =19, LcSSc=6) and comparable sites on healthy controls (HC) (n=10) were collected using the dermal suction blister method. These were profiled by Luminex array for inflammatory cytokines, chemokines, and growth factors. Permutation analysis (SAM in EXCEL) was used to compare cytokine levels in SSc and HC samples.

Results:

Luminex array profiling of the dermal blister fluid showed increased inflammatory cytokines (mean IL-6 in SSc 77.2 pg/ml versus 17.8 pg/ml in HC p=0.009, mean IL-17 in SSc  0.61 pg/ml versus 0 pg/ml, p=0.03), and vascular growth factors (VEGF 21.7 pg/ml in SSc, 13.5 pg/ml in HC (p=NS) and PDGF-aa 16.4 pg/ml in SSc versus 0.97 pg/ ml in HC, p=0.049). Additionally MCP-3 (CCL7), IL-15, and IFN-g were all found to be significantly increased in SSc compared to HC (p<0.05) (Figure 1).

Subanalysis highlighted a correlation between IL-6 and skin score (r=0.44, p=0.024) in SSc, and MCP-3 with disease duration (r=0.54, p=0.005). There was also a significant correlation between IL-6 and IL-10 (r=0.59, p=0.002)

IFN-g, IL-17, PDGF-bb were largely undetectable in the blister fluid of HC, but were present in a subgroup of SSc patients. IL-17 was only detectable in DcSSc (5/19), and in 0/6 LcSSc and 0/10 HC, while IFN-g was present in the blister fluid of 1/10 HC, and 15/25 SSc. IFN-g levels were higher in the diffuse subset compared to those with limited disease (mean 1.76 pg/ml and 0.67pg/ml respectively). IL-6 showed a trend towards increased concentrations in DcSSc compared to LcSSc, but this was not statistically significant (mean 71.7 pg/ml in DcSSc, 32.3 pg/ml in LcSSc, p=0.07).

Conclusion:

Our results confirm the potential utility of dermal blister fluid to non-invasively define local biological processes in SSc, and identify profibrotic, angiogenic and T-cell derived factors expressed locally within the skin lesions. This technique of profiling patients using blister fluid has the potential to complement clinical and gene expression based classification to facilitate targeted therapy, as well as providing potential markers of disease activity or treatment effect.

Figure 1: Graph to show mean concentration of MCP-3, PDGF-AA, IL-6, IL-17a and IFN-gamma in SSc patients and healthy controls.