Pathogenesis of severe pneumonia: advances and knowledge gaps.

PURPOSE OF REVIEW: Pneumonia is a common disease that becomes severe in a subset of patients, dependent on host biology including mechanisms of immune resistance and tissue resilience. This review emphasizes discoveries in pneumonia biology from 2016, highlighting questions and directions that are especially pressing or newly emerging. RECENT
FINDINGS: Novel cell-cell interactions mediating innate immune responses against microbes in the lung have been elucidated, between distinct leukocyte subtypes as well as between leukocytes and the structural cells of the lung. Adaptive immunity has received growing attention for determining the outcome of pneumonia, particularly the lung resident memory cells that arise from repeated prior respiratory infections and direct heterotypic recall responses. New tissue resilience components have been identified that contribute to anti-inflammatory, proresolution, tissue-protective, and reparative regeneration pathways in the infected lung.
SUMMARY: Recent findings will direct research into fundamental mechanisms of lung protection. Over the longer term, manipulating these pathways has implications for clinical practice, as strategies to bolster resistance and resilience have potential to ameliorate severe pneumonia.