Circulating dendritic cells and asthma: Rapid changes following inhaled allergen

Dendritic cells (DC) are thought to play a key role in the initiation and maintenance of T-cell immunity to inhaled antigens. DC density within the bronchial mucosa is increased in stable asthma, and we previously showed a significant reduction in numbers of circulating DC within 24 hours of allergen inhalation (AJRCCM 1998;157: A871). However, the kinetics of this DC response is not clear. Using flow cytometry, we enumerated absolute numbers of blood DC and other leukocytes in 9 mild asthmatics, before and after allergen challenge. Data are expressed as a percentage of baseline values prior to allergen challenge (*p < 0.05 versus baseline). 3h 6h 24h post challenge Dendritic cells 63.1 ±20.3* 62.8±17.2* 78.0±22.2* Lymphocytes 87.1 ±15.1* 75.4±14.1* 88.6±13.5* Monocytes 95.0±12.6 98.5±25.9 99.5±10.5 Eosinophils 82.1±28.2 71.6±24.6* 117.3±24.5 Granulocytes 116.6±28.4 116.3±34.9 80.3±11.2* We conclude that allergen challenge is associated with rapid reductions in numbers of circulating DC and lymphocytes, whereas changes in other circulating leukocytes occurred more slowly (eosinophils & granulocytes), or were not detectable (monocytes). These findings imply that margination of circulating DC and subsequent recruitment into the airways is initiated very rapidly following allergen inhalation.