In a recent study performed on 39 taxi drivers potentially exposed to emissions, a positive linear correlation between 1-OHP levels and pro-inflammatory cytokines (IL 1β (r = 0.37, p = 0.007), IL-6 (r = 0.32, p = 0.02) and TNFα (r = 0.33, p = 0.02)) was reported [28], suggesting a weak correlation between PAH exposure and TNFα mRNA and protein expression. This evidence concerns the gene IL6 and pulmonary arterial hypertension.