GM-CSF-licensed CD11b⁺ lung dendritic cells orchestrate Th2 immunity to Blomia tropicalis

The Blomia tropicalis dust mite is prevalent in tropical and subtropical regions of the world. Although it is a leading cause of asthma, little is known how it induces allergy. Using a novel murine asthma model induced by intranasal exposure to B. tropicalis, we observed that a single intranasal sensitization to B. tropicalis extract induces strong Th2 priming in the lung draining lymph node. Resident CD11b⁺ dendritic cells (DCs) preferentially transport Ag from the lung to the draining lymph node and are crucial for the initiation of Th2 CD4⁺ T cell responses. As a consequence, mice selectively deficient in CD11b⁺ DCs exhibited attenuated Th2 responses and more importantly did not develop any allergic inflammation. Conversely, mice deficient in CD103⁺ DCs and CCR2-dependent monocyte-derived DCs exhibited similar allergic inflammation compared with their wild-type counterparts. We also show that CD11b⁺ DCs constitutively express higher levels of GM-CSF receptor compared with CD103⁺ DCs and are thus selectively licensed by lung epithelial-derived GM-CSF to induce Th2 immunity. Taken together, our study identifies GM-CSF- licensed CD11b ⁺ lung DCs as a key component for induction of Th2 responses and represents a potential target for therapeutic intervention in allergy.