Guest editorial (Mini-symposium: innate immunity in the lung)

The lungs are exposed constantly to an environment full of potential pathogens and noxious agents that have the ability to damage them and compromise the host. The immune response has evolved to such a high degree that we can exist in this environment, maintaining the lungs in a relatively sterile state but still free of inflammation that would impair their ability to function. In the last 150 years, as we began to appreciate the role of microorganisms in causing infection, we have also begun to understand how the immune system has evolved to deal with these challenges. The immune system is broadly divided into functional components known as the innate and adaptive immune responses. The innate immune response is an ancient system that has evolved with the development of multicellular organisms and is remarkably similar in both animals and plants, suggesting that it had evolved prior to the split of these organisms into their separate kingdoms. In contrast, the adaptive immune response is seen only in vertebrates and has evolved only in addition to the innate immune response and is therefore dependent upon it. Serious dysfunction of the innate immune response is not compatible with life, which emphasizes its importance. Recent advances have revealed its complexity in terms of host defence and its interaction with the adaptive immune response. The importance of the innate immune response in lung defence and its role in pulmonary disease is the subject of this review series