Myeloid dendritic cells type 2 after allergen inhalation in asthmatic subjects

Background Dendritic cells (DCs) are professional antigen-presenting cells that mediate the response to inhaled allergen. A major division in DC ontogeny exists between myeloid DCs (mDCs) and plasmacytoid DCs (pDCs). A subtype of mDC expressing thrombomodulin, termed myeloid DCs type 2 (mDC2s), has been identified in both the circulation and lung and has recently been suggested to have a role in allergic asthma. Objective To investigate changes in circulating and sputum mDC2s after allergen inhalation in subjects with asthma. Methods Peripheral blood and induced sputum were obtained before and 3, 7, and 24h after inhalation of diluent and allergen from allergic asthmatic subjects who develop both allergen-induced early- and late-phase responses. mDC2s were measured by flow cytometry. Soluble BDCA-3 (thrombomodulin) was measured in sputum by ELISA. Results The number of sputum mDC2s significantly increased 24h after allergen challenge compared with diluent. The expression of BDCA-3 on sputum mDCs also increased, albeit non-significantly, at 7 and 24h after allergen. Soluble BDCA-3 in sputum and the number of circulating mDC2s were not different between allergen and diluent. Conclusions and clinical relevance Myeloid DCs type 2 (mDC2s) increase in the sputum of subjects with asthma after allergen challenge, suggesting this subtype of mDC is involved in the regulation of allergen responses in the lung.