Circulating levels of sTNFR and discrepancy between cytotoxicity and immunoreactivity of TNF-α in patients with visceral leishmaniasis

Abstract

To study the influence of soluble tumour necrosis factor (TNF) receptors (sTNFR) on bioactivity and immunoreactivity of TNF-alpha in patients with visceral leishmaniasis (Kala-azar) and to examine the association between circulating levels of sTNFR type I and type II with clinical manifestations of the disease. Ten patients with Kala-azar were enrolled. Plasma samples for TNF-alpha and sTNFR were obtained on days 0, 7 and 21-28 of antimonial therapy. Bioactivity of TNF-alpha was measured by cytotoxicity to L-929 cells and immunoreactivity by enzyme-linked immunosorbent assay (ELISA). sTNFR-I and sTNFR-II were measured by ELISA. Measured by ELISA, TNF-alpha was detected at baseline in all patients (range from 22.3 to 163 pg/mL) and showed a linear decline over time on therapy (r = -0.49, P = 0.007). In contrast, when measured by cytotoxicity assay, TNF-alpha was detected in only one patient at baseline (193 pg/mL) and in four patients at the end of therapy (38.7, 95, 133 and 232 pg/mL) and there was no linear association between TNF-alpha and duration of therapy (r = -0.18, P = 0.45). sTNFR-I and sTNFR-II were detected in all patients before therapy. There was a strong positive correlation between plasma concentrations of sTNFR-I and sTNFR-II (r = 0.8, P = 0.006). Levels of sTNFR-I and sTNFR-II declined exponentially with time on therapy. We concluded that sTNFR-I and sTNFR-II are related to disease activity in patients with Kala-azar and that these circulating receptors may interfere with the biological activity of TNF-alpha in patients with Kala-azar.