Genetic susceptibility to ozone-induced lung hyperpermeability - Role of toll-like receptor 4

The pollutant ozone (O-3) induces lung hyperpermeability and inflammation i n humans and animal models. Among inbred strains of mice, there is a 3-fold difference in total protein (a marker of permeability) recovered in bronch oalveolar lavage (BAL) fluid after a 72-h exposure to 0.3 ppm O-3. To deter mine the chromosomal locations of susceptibility genes, we performed a geno me screen using recombinant inbred (RI) strains of mice derived from O-3-su sceptible C57BL/6J (B6) and Os-resistant C3H/HeJ (HeJ) progenitors. Each RI strain was phenotyped for O-3-induced hyperpermeability, and linkage was a ssessed for 558 markers using Map Manager QTb27. A significant quantitative trait locus (QTL) was identified on chromosome 4. The likelihood ratio chi (2) statistic (16.6) for the peak of the QTL was greater than the significa nce threshold (16.3) determined empirically by permutation test. This QTL c ontains a candidate gene, Toll-like receptor 4 (TIr4), that recently has be en implicated in innate immunity and endotoxin susceptibility. The amount o f the total trait variance explained by the QTL at TIr4, the gene with the highest likelihood ratio statistic in the QTL was approximately 70%. To tes t the role of TIr4 in O-3-induced hyperpermeability, BAL protein responses to O-3 were compared in C3H/HeOuJ (OuJ) and HeJ mice that differ only at a polymorphism in the coding region of TIr4. Significantly greater protein co ncentrations (430 +/- 35 mu g/ml) were found in OuJ mice compared with HeJ mice (258 +/- 18 mu g/ml) after exposure to O-3 Furthermore, reverse transc riptase/polymerase chain reaction analysis demonstrated differential expres sion of TIr4 message levels between He] and OuJ mice after O-3 exposure. To gether, results indicate that a QTL on mouse chromosome 4 explains a signif icant portion of the genetic variance in O-3-induced hyperpermeability, and support a role for TIr4 as a strong candidate susceptibility gene.