Mycobacterium bovis BCG has been shown to down-regulate experimental allergic asthma a finding that reinforced the hygiene hypothesis. We have previously found that recombinant BCG (rBCG) strain that express the genetically detoxified S1 subunit of pertussis toxin (rBCG-S1PT) exerts adjuvant effect that enhance Th1 responses against BCG proteins. Here we investigated the effect of this rBCG-S1PT on the classical OVA-induced mouse model of allergic lung disease. We found that rBCG-S1PT was more effective than wild-type BCG in preventing Th2-mediated allergic immune responses. The inhibition of allergic lung disease was not associated with increased concentration of suppressive cytokines or with an increased number of pulmonary regulatory T cells, but was positively correlated with the increase in IFN- producing T cells and T-bet expression in the lung. In addition, an IL-12-dependent mechanism appeared to be important to the inhibition of lung allergic disease. Notably, the inhibition of allergic inflammation was found to be restricted to the lung because when allergen challenge was given by the intraperitoneal route, rBCG-S1PT administration failed to inhibit peritoneal allergic inflammation and type 2 cytokine production. Our work offers a non classical interpretation for the hygiene hypothesis indicating that attenuation of lung allergy by rBCG could be due to the enhancement of local lung Th1 immunity induced by rBCG-S1PT. Moreover, it highlights the possible use of rBCG strains as multipurpose immunomodulators by inducing specific immunity against microbial products and at the same time protecting against allergic asthma.