Differential roles of lung dendritic cell subsets against respiratory virus infection

Respiratory viruses can induce acute respiratory disease. Clinical symptoms and manifestations are dependent on interactions between the virus and host immune system. Dendritic cells (DCs), along with alveolar macrophages, constitute the first line of sentinel cells in the innate immune response against respiratory viral infection. DCs play an essential role in regulating the immune response by bridging innate and adaptive immunity. In the steady state, lung DCs can be subdivided into CD103(+) conventional DCs (cDCs), CD11b(+) cDCs, and plasmacytoid DCs (pDCs). In the inflammatory state, like a respiratory viral infection, monocyte-derived DCs (moDCs) are recruited to the lung. In inflammatory lung, discrimination between moDCs and CD11b(+) DCs in the inflamed lung has been a critical challenge in understanding their role in the antiviral response. In particular, CD103(+) cDCs migrate from the intraepithelial base to the draining mediastinal lymph nodes to primarily induce the CD8(+) T cell response against the invading virus. Lymphoid CD8α(+) cDCs, which have a developmental relationship with CD103(+) cDCs, also play an important role in viral antigen presentation. Moreover, pDCs have been reported to promote an antiviral response by inducing type I interferon production rather than adaptive immunity. However, the role of these cells in respiratory infections remains unclear. These different DC subsets have functional specialization against respiratory viral infection. Under certain viral infection, contextually controlling the balance of these specialized DC subsets is important for an effective immune response and maintenance of homeostasis.