Dysregulation of Allergic Airway Inflammation in the Absence of Microbial Colonization

Rationale: The incidence of allergic disorders is increasing in developed countries and has been associated with reduced exposure to microbes and alterations in the commensal bacterial flora.Objectives: To ascertain the relevance of commensal bacteria on the development of an allergic response, we used a model of allergic airway inflammation in germ-free (GF) mice that lack any exposure to pathogenic or nonpathogenic microorganisms.Methods: Allergic airway inflammation was induced in GF, specific pathogen–free (SPF), or recolonized mice by sensitization and challenge with ovalbumin. The resulting cellular infiltrate and cytokine production were measured.Measurements and Main Results: Our results show that the total number of infiltrating lymphocytes and eosinophils were elevated in the airways of allergic GF mice compared with control SPF mice, and that this increase could be reversed by recolonization of GF mice with the complex commensal flora of SPF mice. Exaggerated airway eosinophilia correlated with...