Potential applicability of cytokines as biomarkers of disease activity in rheumatoid arthritis: Enzyme-linked immunosorbent spot assay-based evaluation of TNF-α, IL-1β, IL-10 and IL-17A.

Biomarkers play a pivotal role in the management of rheumatoid arthritis (RA) by facilitating early diagnosis and 'treat to the target.' However, no gold standard biomarker has been identified for monitoring the disease activity in RA. Cytokines, a diverse group of small protein molecules secreted by peripheral blood mononuclear cells (PBMCs), play a pivotal role in pathogenesis and disease progression in RA. Research is currently underway to find out the applicability of cytokines as biomarkers in RA. This study aimed to quantify the PBMCs that secrete four types of cytokines; TNF-α, IL-1β, IL-10 and IL-17A in two cohorts of active RA patients (early RA patients and established RA patients), compared to healthy controls (HC), using the enzyme-linked immunosorbent spot (ELISPOT) assay, and to assess their association with measures of disease activity of RA. Patients were recruited from outpatient rheumatology clinics, and the disease activity was assessed using single and composite measures of disease activity. The cytokine expression was evaluated using freshly separated PBMCs from whole blood of RA patients using the ELISPOT assay. The number of PBMCs (counted as spot-forming cells (SFCs) per 105 PBMCs) that secreted the cytokine of interest were statistically significantly higher in early RA patients, compared to HC, for IL-17A (P<0.05). Such an increased number of SFCs was not observed in the established RA group, compared to controls, for any of the cytokines tested. The correlation analysis showed that IL-17A is having a moderate correlation (Spearman`s ρ, p <0.05) with five clinical measures of disease activity, including disease activity score 28 (DAS28). According to the multivariable linear regression models, IL17A was a good predictor of both the disease activity score 28 (DAS28) and clinical disease activity index (CDAI). In conclusion, IL-17A has potential applicability as a biomarker of disease activity of RA.