Secondhand Smoke Induces Allergic Sensitization in Mice

Abstract

Purpose of the Study. Although there is evidence that environmental tobacco smoke (ETS) can exacerbate allergic responses, the role of ETS in primary allergic sensitization remains unclear. The objective of this study was to examine the influence of ETS on allergic sensitization in a mouse model.Study Population. Female BALB/c and C57BL/6 mice.Methods. The investigators exposed mice to either ovalbumin (OVA), saline, ETS, or OVA + ETS by nebulization. Total IgE and OVA-specific immunoglobulin E (IgE), IgG1 and IgG2a were quantified for each of the 4 exposure groups. Mice were reexposed to nebulized OVA 30 days after the initial exposure and cytokine levels in bronchoalveolar lavage (BAL) fluid were measured. Interleukin (IL)-2, IL-4, IL-5, IFN-γ and granulocyte-macrophage colony-stimulating factor (GM-CSF) were measured to look for evidence of Th1 or Th2 skewed immune responses. Two strains of mice were studied, BALB/c, a high IgE producer, and C57BL/6, a low IgE producer.Results. An allergic antibody response, as measured by total IgE and OVA-specific IgE and IgG1, was present in C57BL/6 mice exposed to OVA + ETS, but was not detectable in those exposed to saline, OVA alone, or ETS alone. The results were statistically significant. The allergic antibody response in the BALB/c mice was also most pronounced in the group exposed to OVA + ETS. As this strain more readily produces IgE, there was detectable total IgE as well as OVA-specific IgE and IgG1 in the group exposed to OVA alone, but levels of OVA-specific IgE and IgG1 were statistically significantly higher in the OVA + ETS group. BAL fluid was examined for eosinophilia after rechallenge with OVA in C57BL/6 mice. The OVA + ETS group had marked eosonophilia while the saline, OVA and ETS groups had no eosinophils. Cytokines were also quantified in BAL fluid. IFN-γ, a Th1-associated cytokine, was decreased in OVA + ETS mice as compared with the OVA-exposed group (P < .01), while IL-5, a Th2-associated cytokine, was increased as compared with the OVA-exposed group (P < .05).Conclusion. ETS exposure appears to facilitate the primary allergic response in mice as measured by allergic antibody response and BAL cytokine response and eosinophilia.Reviewers’ Comments. Although some evidence has been published regarding ETS and its role in exacerbating allergic responses, this is the first study demonstrating a significant role for ETS in primary allergic sensitization in mice. Future studies will no doubt address the applicability of these findings to humans.