The pulmonary dendritic/langerhans cell in immunity and disease

Dendritic cells are potent antigen-presenting cells located in strategic positions in the lung, enabling them to be a first line of defense against inhaled pathogens. These cells are a critical component of the immune system, and surveillance of tissues for emerging tumors, infectious pathogens, and cellular breakdown products relies to a large extent on dendritic cells. Langerhans cells are a specialized type of dendritic cell, distributed in a subepithelial location in the airways. At least 1 other population of non-Langerhans type of dendritic cells exists in the lung, distributed in the interstitial and pleural spaces. These phagocytic dendritic cells are able to activate upon contact with antigen or exposure to proinflammatory factors. Upon activation, they become migratory and transport antigens from the airways or distal lung spaces to the draining lymph nodes, where processed antigen is presented to T cells. In addition to eliciting specific T-cell responses to antigens, pulmonary dendritic cells also induce tolerance to innocuous antigens through the induction of regulatory T cells. Defective dendritic cell function plays an important role in numerous lung diseases. Understanding the origin, function, and interactions between dendritic cells and other resident airway and interstitial cells may provide key insight into many lung diseases, including asthma and interstitial lung diseases. Abnormalities in dendritic cell function have been implicated in the development of cancer, and ongoing research suggests that these cells may be used as an immune adjuvant to enable eradication of established lung cancer or prevent the development of metastases.