Infection and Inflammation: A Double-Edged Sword

Appropriate host inflammatory response is crucial to control infections. This entails the recruitment of the immune system cells, mainly innate immunity, and the production of multiple mediators. The inability to activate all the components of the inflammation cascade can lead to the survival of the invading microorganism and consequent progression of the induced tissue damage, disruption of normal homeostasis, and multi-organ failure. On the other hand, the host response itself can cause body damage, as an uncontrolled and dysregulated inflammatory response can also lead to disrupted homeostasis and organ failure. The inflammatory response can thus be a double-edged sword. This perception is reviewed with new data that highlight three distinct aspects of the complicated issue. First is hyper-inflammation following a viral infection, as depicted by the current pandemic of coronavirus disease 2019 (COVID-19) and its consequences in adults and children. Second is brain inflammation during a bacterial infection caused by Shigella species as documented in humans and in an animal model, and the short- and long-term impacts on neuropsychiatric disorders. Third is the novel attempt to use the components of the host inflammatory response in order to aid clinicians in distinguishing between bacterial and viral infections and thus to improve patient management.