CD34 is required for dendritic cell trafficking and pathology in murine hypersensitivity pneumonitis

Rationale: Although recent work has shown that CD34 plays an important role in the trafficking of inflammatory cells during Th2-biased inflammatory responses, its role in Th1/Th17-biased disease as well as dendritic cell (DC) trafficking is unknown. Objectives: We used CD34-deficient mice (Cd342/2) to investigate the role of CD34 in the Th1/Th17-biased lung inflammatory disease, hypersensitivity pneumonitis (HP). Methods: HP was induced in wild-type (wt) and Cd34 -/- mice by repeated intranasal administration of Saccharopolyspora rectivirgula antigen. Lung inflammation was assessed by histology and analysis of bronchoalveolar lavage cells. Primary and secondary immune responses were evaluated by cytokine recall responses of pulmonary inflammatory cells as well as draining lymph node cells. Measurements and Main Results: Cd34 -/- mice were highly resistant to the development of HP and exhibited an inflammatory pattern more reflective of a primary response to S. rectivirgula rather than the chronic lymphocytosis that is typical of this disease. Cytokine recall responses from Cd34 -/- lymph node cells were dampened and consistent with a failure of antigen-loaded Cd34 -/- DCs to deliver antigen and prime T cells in the draining lymphnodes. Inagreement with this interpretation, adoptive transfer of wt DCs into Cd34 -/- mice was sufficient to restore normal sensitivity to HP. CD34 was found to be expressed by wt DCs, and Cd342/2 DCs exhibited an impaired ability to chemotax toward a subset of chemokines in vitro. Finally, expression of human CD34 in Cd34 -/- mice restored normal susceptibility to HP. Conclusions: We conclude that CD34 is expressed by mucosal DCs and plays an important role in their trafficking through the lung and to the lymph nodes. Our data also suggest that CD34 may play a selective role in the efficient migration of these cells to a subset of chemokines.