Secondhand smoke induces allergic sensitization in mice

Epidemiological studies have suggested increased prevalence of atopy in children of maternal smokers. Although secondhand smoke or environmental tobacco smoke (ETS) has been shown to augment allergic responses, its role in atopic sensitization is still controversial. We studied whether ETS could initiate a Th2 response and thus induce primary allergic sensitization. Mice were exposed for 10 consecutive days to either 1% aerosolized OVA, ETS (5 cigarettes), or both ETS and OVA. C57BL/6 mice receiving both ETS and OVA developed OVA-specific IgE and IgG1, 12, 14, and 25 days after the initial exposure, whereas those receiving OVA alone did not. Thirty days after the initial challenge (20 days after its completion), mice were re-exposed to OVA. Bronchoalveolar lavage performed 24 h later revealed an influx of eosinophils in the group initially challenged with both ETS and OVA, but not in those exposed to ETS alone or OVA alone. Increases in IL-5, GM-CSF, and IL-2 were observed in bronchoalveolar lavage from this OVA/ETS-exposed group, whereas IFN-gamma levels were significantly inhibited. These results suggest that ETS can induce allergic sensitization to a normally harmless Ag, and they may explain why secondhand smoke is a major risk factor for the development of allergy in children.