Differential effects of asymptomatic Ascaris lumbricoides, Schistosoma mansoni or hook worm infection on the frequency and TGF-beta-producing capacity of regulatory T cells during active tuberculosis

Abstract

Helminth induced expansion of regulatory T cells (Tregs) may take part in suppressing protective host responses during tuberculosis (TB), although Tregs functionality and link to TB disease severity remains unexplored. We investigated the species-specific effect of helminths on frequency and TGF-β producing capacity of Tregs, and possible connection to TB disease severity. 89 pulmonary TB patients (PTB) and 69 community controls (CCs) from Gondar, Ethiopia, were included. Clinical disease severity was graded by TB score, and flow cytometry used to characterize Treg frequency and functionality measured as their TGF-β-producing capacity. In helminth positive PTB patients (Helminth+PTB+) compared to helminth negative PTB or CCs, TGF-β+ Tregs were significantly increased mainly in hookworm coinfection whereas S. mansoni increased TGF-β+ Tregs in CCs. Treatment of TB and helminths decreased TGF-β+ Tregs in Helminth+PTB+ at 2 months follow-up. There were no overall differences in the frequency of Tregs in CCs or PTB unless stratification on TB disease severity was performed. At inclusion Helminth+PTB+ had increased frequency of Tregs already at low disease severity, and TGF-β+ Tregs correlated to intermediate-to-high disease severity. In conclusion, helminth specific increase of TGF-β+ Tregs in PTB patients was correlated to TB disease severity and was restored following anti-helminth treatment.