Figure 2.

PMNs responses during health and disease. Normal PMN function includes low level recruitment to healthy mucosal tissues to limit growth of the commensal biofilm. Pathogenic factors including infection, injury, and cancer trigger inflammatory PMN responses. In the case of an effective response homeostasis/health is achieved. If not this can lead to chronic inflammation or death. Non-resolving chronic inflammation can produce PMN mediated tissue damage and dysbiosis of commensal microbes, which leads to further exacerbation of inflammation. Underlying chronic inflammatory conditions, which are common in the elderly, increase the risk of severe hyper-inflammatory responses to an unrelated secondary inflammatory trigger. These hyper-inflammatory PMN-mediated responses including sepsis and ARDS, and are associated with high mortality. Hyperactive or defective inflammatory responses can also occur due to genetic conditions or old age, leading to dysbiosis, chronic inflammation, and tissue damage. PMN targeted therapies can help mitigate these defects to promote normal PMN function and health.