Intranasal priming of newborn mice with microbial extracts increases opsonic factors and mature CD11c+ cells in the airway

Nasal exposure to the mixture of microbial extracts (MME) after ablactation enhanced airway resistance of newborn mice to Streptococcus pneumoniae (J Physiol Lung Cell Mol Physiol 298: L67, 2010). The present study was addressed to elucidate effective factors responsible for the enhanced innate resistance in the airway of MME-exposed newborn mice. MME exposure significantly increased the amount of pulmonary surfactants (SP-A and SP-D) in the airway. Bronchoalveolar lavage fluid of the exposed mice exhibited greater levels of opsonic activity, thereby enhancing the phagocytic and intracellular killing activities of alveolar macrophages (MO) against S. pneumoniae. The exposure itself did not increase a complement component C3 and mannan-binding lectin-A (MBL-A) in the airway, whereas intratracheal infection with S. pneumoniae increased the quantity of SP-A, SP-D, C3, and MBL-A in the exposed mice to a significant extent compared with control mice. The exposure enhanced the expression of the class A scavenge...