Background: Toll-like receptor 4 (TLR4) variants have been shown to reduce the respiratory responses to inhaled LPS in controlled experiments among healthy volunteers.
Objective: We sought to investigate whether naive subjects with TLR4 variants showed reduced respiratory response to a complex aerosol including endotoxin as a major constituent.
Methods: Twenty-nine nonsmoking, nonatopic healthy subjects with TLR4 299/399 polymorphisms and 29 age- and sex-matched, wild-type TLR4 control subjects were exposed for 5 hours each in a noncontaminated environment (baseline day) and in a swine confinement facility (exposure day). There were 16 men and 13 women in each of the 2 age- and sex-matched groups.
Results: TLR4 polymorphic subjects who were exposed to high endotoxin levels (>or=1550 EU/m(3)) had less reduction in the percentage across-shift change in FEV(1) from baseline than did wild-type subjects exposed to similar endotoxin levels. Among subjects exposed to higher endotoxin levels, the mean differences in the percentage across-shift changes between baseline and exposure days were significantly less in TLR4 polymorphic subjects compared with those seen in wild-type subjects in FEV(1) (-8.48% +/- 1.52% [mean +/- SE] vs -11.46% +/- 1.79%, P = .001), forced expiratory flow between 25% and 75% of forced vital capacity (-18.30% +/- 1.99% vs -24.14% +/- 3.28%, P = .009), and FEV(1)/forced vital capacity ratio (-5.40% +/- 0.56% vs -8.53% +/- 1.51%, P = .04). These patterns were not observed in IL-6 levels from serum and nasal lavage fluid, IL-8 levels from nasal lavage fluid, white blood cell counts, or blood differential counts.
Conclusion: The association between TLR4 variants and reduced airway responsiveness to inhaled particulate was observed at high endotoxin concentrations, creating the possibility of certain threshold phenomena for the apparent protective effect of TLR4 variants.