Influenza-derived peptides cross-react with allergens and provide asthma protection.

BACKGROUND: The hygiene hypothesis is the leading concept to explain the current asthma epidemic, which is built on the observation that a lack of bacterial contact early in life induces allergic TH 2 immune responses.

OBJECTIVE: Because little is known about the contribution of respiratory tract viruses in this context, we evaluated the effect of prior influenza infection on the development of allergic asthma.

METHODS: Mice were infected with influenza and, once recovered, subjected to an ovalbumin- or house dust mite-induced experimental asthma protocol. Influenza-polarized effector memory T (Tem) cells were transferred adoptively to allergen-sensitized animals before allergen challenge. A comprehensive in silico analysis assessed homologies between virus- and allergen-derived proteins. Influenza-polarized Tem cells were stimulated ex vivo with candidate peptides. Mice were immunized with a pool of virus-derived T-cell epitopes.

RESULTS: In 2 murine models we found a long-lasting preventive effect against experimental asthma features. Protection could be attributed about equally to CD4+ and CD8+ Tem cells from influenza-infected mice. An in silico bioinformatic analysis identified 4 influenza- and 3 allergen-derived MHC class I and MHC class II candidate T-cell epitopes with potential antigen-specific cross-reactivity between influenza and allergens. Lymphocytes from influenza-infected mice produced IFN-γ and IL-2 but not IL-5 on stimulation with the aforementioned peptides. Immunization with a mixture of the influenza peptides conferred asthma protection, and peptide-immunized mice transferred protection through CD4+ and CD8+ Tem cells.

CONCLUSION: For the first time, our results illustrate heterologous immunity of virus-infected animals toward allergens. This finding extends the original hygiene hypothesis.