There is much variability between individuals in the response to inhaled toxins, but it is not known why certain people develop disease when challenged with environmental agents and others remain healthy. To address this, we investigated whether TLR4 (encoding the toll-like receptor-4), which has been shown to affect lipopolysaccharide (LPS) responsiveness in mice1,2, underlies the variability in airway responsiveness to inhaled LPS in humans3. Here we show that common, co-segregating missense mutations (Asp299Gly and Thr399Ile) affecting the extracellular domain of the TLR4 receptor are associated with a blunted response to inhaled LPS in humans. Transfection of THP-1 cells demonstrates that the Asp299Gly mutation (but not the Thr399Ile mutation) interrupts TLR4-mediated LPS signalling. Moreover, the wild-type allele of TLR4 rescues the LPS hyporesponsive phenotype in either primary airway epithelial cells or alveolar macrophages obtained from individuals with the TLR4 mutations. Our findings provide the first genetic evidence that common mutations in TLR4 are associated with differences in LPS responsiveness in humans, and demonstrate that gene-sequence changes can alter the ability of the host to respond to environmental stress.
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We thank C. Galer, T. Grunst, M. Malik, N. Meyer, M. Monick, K. Schneider and S. Swartz for technical assistance; the University of Iowa Airway Epithelia Cell Culture Core and Gene Transfer Vector Core; and M. Welsh and J. Murray for discussions. This study was supported by grants from the Department of Veterans' Affairs (Merit Review), the National Institute of Environmental Health Sciences (ES06537, ES07498 and ES09607), the National Heart Lung and Blood Institute (HL62628 and HL64855) and the General Clinical Research Centers Program (RR00059).
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