Inflammageing and Immune Responses in the Lung
Structural changes of the ageing lung are regulated by genetically coded and acquired qualities that are tightly interconnected with systemic immune dysfunction and chronic, low level systemic inflammation, termed inflammageing. Inflammageing is the basal activation of the innate immune system in the absence of an immunologic threat  and is marked by elevated levels of tissue and circulating pro-inflammatory cytokines including interleukin (IL)-1p, IL-6, and tumour necrosis factor-a (TNF-a). Inflammageing combined with blunted innate and adaptive immune responses (see Chaps. 1 and 2) affects the lungs ability to fight infections and also leads to tissue remodelling.
In the adult healthy lung several immune cell types are resident at various anatomical sites including bronchial, interstitial and alveolar macrophages, dendritic cells, interstitial T- and B-lymphocytes . Their presence is highly important as our lungs are in constant and direct contact with the environment via epithelial surfaces. During ventilation the lung surfaces are exposed to various microbes, particles and potentially damaging physical forces. Together with a variety of pulmonary epithelial cell types, the resident macrophages, T-cells and dendritic cells orchestrate the active protection of the lung tissue. During ageing the same is expected of the above cell types; however, immune cells change with age and their response to stimuli is no longer the same as in a young, healthy adult (see Chaps. 1 and 2).
The immunological defence of the lungs employs both innate and adaptive immune responses against antigens. Innate immunity is the critical first line of defence for the lungs while adaptive (acquired) immunity is antigen-specific and is required to ward off encapsulated bacteria, viruses, and intracellular pathogens. This form of immunity relies on immunological memory and antibody production. However, important changes in immunological responses occur with age and the impact on lung immunity can be summarised as follows: