Allergen Exposure Increases Triggering Receptor Expressed on Myeloid Cell (TREM)-2 Expression on Lung Dendritic Cell Subsets in a Murine Model of Asthma

Rationale: Dendritic cells (DCs) are professional antigen presenting cells which traffic from the lungs to the lymph nodes to present processed antigens to T-cells driving an inflammatory (Th2) response in atopic individuals. The recently discovered TREM-2 surface receptor has been shown to be expressed on dendritic cells; however, its role in asthma is yet to be elucidated. Here, we examined the effect of allergen exposure on TREM-2 expression in the airways and on lung DC subsets. 

Methods: Female Balb/c mice were sensitized and challenged with ovalbumin or PBS for a total of 20 days.  Lung tissues from both groups were harvested and examined for protein and mRNA expression of TREM-2. DCs were sorted using autoMACS and FACS to determine TREM-2 -positive lung DC subsets. 

Results: Sensitization and challenge with ovalbumin resulted in increased airway hyper-responsiveness, mucus secretion, airway eosinophilia, and total IgE in serum and BALF. TREM-2 mRNA expression in whole lung was significantly higher (p<0.05) in the allergen-sensitized and challenged mice which was associated with increased protein expression in the lungs. Analysis of CD11c⁺MHC-II^hi lung DCs revealed that the OVA-sensitized and challenged group had greater density of cells that were CD11b⁺CD103^- and CD11b⁺CD103⁺ compared to the control. TREM-2 expression was significantly higher (p<0.01) on the CD11b⁺CD103⁺ cells when compared to the CD11b⁺CD103^- cells. 

Conclusions: Allergen-sensitization and challenge increases the expression of TREM-2 in the airways and on the surface of lung DC subsets which may contribute to increased airway inflammation in allergic asthma.