Dendritic cells in the mucosa of the human trachea are not regularly found in the first year of life

Background-Dendritic cells (DCs) in the mucosa of the respiratory tract might be involved in the early development of pulmonary allergy or tolerance. To date, little is known about when the first DCs occur in human airways. Methods-Specimens of the distal trachea from patients who had died from sudden death in the first year of life (n=29) and in older age groups (n=59) as well as from those who had died from respiratory tract infections in the first year of life (n=8) were examined by immunohistochemistry. Transmission electron microscopy was performed in additional samples from two adults. Results-In the sudden death subgroup DCs were absent in 76% of those who died in the first year of life but were present in 53 of the 59 older cases. All infants who had died of respiratory infectious diseases had DCs in the tracheal mucosa. Conclusions-Mature DCs are not constitutively present in the human tracheobronchial mucosa in the first year of life, but their occurrence seems to be triggered by infectious stimuli. These data support the hypothesis that DCs play a crucial role in immunoregulation in early childhood.