RETN and pulmonary emphysema: Studies by Al-daghri et al., Li et al., and Anyenda et al. showed correlations with PAHs and immunoglobulin E IgE, interleukin 4 IL-4 and resistin, increased nitric oxide (NO) and fractional exhaled nitric oxide (FENO) which are biomarkers of childhood asthma and airway inflammation, respectively.8,38,50 However, Shiue et al. reported an inverse association between PAHs and asthma, although it showed a positive association between 2-hydroxyfluorene, 3-hydroxyfluorene and prevalent cases of emphysema.