Impaired TLR5 Functionality Is Associated with Survival in Melioidosis

Abstract

Melioidosis is infection caused by the flagellated saprophyte Burkholderia pseudomallei. TLR5 is a pathogen recognition receptor activated by bacterial flagellin. We studied a genetic variant that encodes a defective TLR5 protein, TLR51174C>T, to elucidate the role of TLR5 in melioidosis. We measured NF-κB activation induced by B. pseudomallei in human embryonic kidney–293 cells transfected with TLR5 and found that B. pseudomallei induced TLR51174C- but not TLR51174T-dependent activation of NF-κB. We tested the association of TLR51174C>T with outcome in 600 Thai subjects with melioidosis. In a dominant model, TLR51174C>T was associated with protection against in-hospital death (adjusted odds ratio: 0.20; 95% confidence interval: 0.08–0.50; p = 0.001) and organ failure (adjusted odds ratio: 0.37; 95% confidence interval: 0.19–0.71; p = 0.003). We analyzed blood cytokine production induced by flagellin or heat-killed B. pseudomallei by TLR51174C>T genotype in healthy subjects. Flagellin induced lower monocyte-normalized levels of IL-6, IL-8, TNF-α, IL-10, MCP-1, IL-1ra, G-CSF, and IL-1β in carriers of TLR51174T compared with carriers of TLR51174C. B. pseudomallei induced lower monocyte-normalized levels of IL-10 in carriers of TLR51174T. We conclude that the hypofunctional genetic variant TLR51174C>T is associated with reduced organ failure and improved survival in melioidosis. This conclusion suggests a deleterious immunoregulatory effect of TLR5 that may be mediated by IL-10 and identifies this receptor as a potential therapeutic target in melioidosis.