Plasma TNF binding capacity in patients with juvenile idiopathic arthritis.
INTRODUCTION: Tumour necrosis factor (TNF)-alpha and TNF-beta, also called lymphotoxin (LT), are bound by soluble truncated TNF receptors (sTNFRI and II) that are released from cell surfaces and act as natural inhibitors of TNF-induced inflammation. We investigated the plasma levels of sTNFRI and II in parallel with LT binding capacity (LTBC) in 44 patients with juvenile chronic arthritis (JIA). METHODS: LTBC was determined by spiking diluted plasma samples with 1000 pg/ml of human recombinant LT. Detectable LT was measured by an in-house ELISA and LTBC was expressed in arbitrary units (AU) as the percentage value of bound LT to added LT. The levels of sTNFRI and-II were measured by ELISA (R&D). RESULTS: We found slightly reduced sTNFRI and II levels in JIA patients (n=44) compared with healthy controls sTNFRI: 1118 pg/ml (656-2074) [mean (range)] vs. 1262 pg/ml (819-2280) p=0.015; sTNFRII: 1953 pg/ml (889-4476) vs. 2311 pg/ml (1309-4186) p=0.008. The sTNFRI levels correlated positively with morning stiffness (r=0.30, p=0.044), physician's global assessment (r=0.39; p=0.009) and CRP (r=0.43; p=0.0048). sTNFRII did not correlate with measures of disease activity. In contrast, patient LTBC values were elevated compared to controls: 44 AU (36-52) vs. 31 AU (13-41) [mean (range)], p<0.0001, but did not correlate with disease activity. CONCLUSION: Despite overall slightly reduced plasma levels of sTNFRI and II, the capacity to bind TNF appeared to be increased in plasma samples from JIA patients.