Reduced levels of circulating progenitor cells in juvenile idiopathic arthritis are counteracted by anti TNF-α therapy

Abstract

Background: Endothelial progenitor cells (EPC) promote angiogenesis and vascular repair. Though reduced EPC levels have been shown in rheumatoid arthritis, no study has so far evaluated EPCs in children with juvenile idiopathic arthritis (JIA). We aimed to study circulating EPCs in children with JIA, their relation to disease activity, and effects of anti TNF-α treatment.

Methods: Circulating EPCs were quantified by flow cytometry based on CD34, CD133 and KDR expression in peripheral blood of 22 patients with oligoarticular JIA and 29 age-matched controls. EPCs were re-assessed in children with methotrexate-resistant oligo-extended JIA before and up to 12 month after initiation of anti-TNF-alpha therapy. Plasma concentrations of inflammatory and EPC-regulating factors were measured using a multiplex array. Confocal immunofluorescence was used to demonstrate EPCs in synovial tissues.

Results: Children with active JIA showed a significant reduction of relative and absolute counts of circulating progenitor cells and EPCs compared to age-matched healthy controls. CD34(+) cell levels were modestly and inversely correlated to disease activity. A strong inverse correlation was found between serum TNF-α and EPC levels. In 8 patients treated with anti TNF-α agents, the number of EPCs rose to values similar to healthy controls. CD34(+)KDR(+) EPCs were found in the synovial tissue of JIA children, but not in control.

Conclusions: Children with JIA have reduced levels of the vasculoprotective and proangiogenic EPCs. While EPCs may contribute to synovial tissue remodelling, EPC pauperization may indicate an excess cardiovascular risk if projected later in life.

Figure 1

Progenitor cell phenotypes in JIA compared to control (CTRL) children. Cell counts are expressed, on different scales, as relative to one million total cytometric events in (A) and as absolute concentration in (B). *p < 0.05 versus CTRL subjects. Generic CPCs include CD34⁺, CD133⁺, CD34⁺CD133⁺ cells, whereas endothelial committed progenitor cells (EPCs) include CD34⁺KDR⁺, CD133⁺KDR⁺, CD34⁺CD133⁺KDR⁺ cells.

Figure 2

Correlation between CD34⁺ cells and disease activity. A significant inverse linear correlation was detected between total CD34⁺ cells and the physician’s visual analogue scale.

Figure 3

Effects of anti-TNF-alpha therapy on the levels of progenitor cell phenotypes and clinical severity. ESR, CRP, VAS and progenitor cell phenotypes were measured at baseline and after 3 and 6 months in 8 children with persistently active JIA. In 3 individuals, a blood sample was also performed at 12 months. *p < 0.05 versus baseline.

Figure 4

Bona fide EPC labelling in synovial tissue of JIA patients. A representative confocal imaging analysis of synovial tissue from a JIA patient (upper lane) and from a child who underwent surgical debridement for a non-inflammatory condition (lower lane). The staining for CD34 and VEGFR-2 (KDR) shows double positive CD34⁺KDR⁺ cells (bona fide EPCs) in clusters or as isolated cells only in the JIA case, while the control was completely negative. Note that, as expected, CD34 also labels microvessels, although at lower intensity compared to isolated EPCs.