Fig. 3.

The Immune pathway in brain–lung axis. The releasing of DAMPs after brain injury could regulate immune system, which relates to the increased risk of pneumonia and ALI. Besides, the brain regulates lung by immune system through the CAP, HPA axis and SAS. Conversely, the over-activated immune systems after pneumonia could damage CNS. Furthermore, SCLC, which promotes the production of multiple autoantibodies, would attack the brain regions that express these antigens in CNS, thus leading to a variety of pathological changes in CNS, e.g., encephalomyelitis, limbic encephalitis, subacute cerebellar degeneration, and other autoimmune encephalitis. BBB blood–brain barrier, HMGB1 high mobility group box 1, MMP-9 matrix metalloproteinases, RAGE receptor for advanced glycation end