Viral pneumonia, on the other hand, is frequently caused by rhinoviruses, coronaviruses, influenza virus, respiratory syncytial virus, adenovirus and parainfluenza[3,4]. Recently, an outbreak of SARS coronavirus 2, a new virus that can progress to pneumonia in infected individuals and that is conventionally known as COVID-19, has been declared a Public Health Emergency of International Concern by the WHO[5].

The immune mechanisms involved in pneumonia infections differs depending on the etiology of the disease. While in viral infections, mononuclear cells are the cellular type frequently linked to the inflammation[6], in bacterial infections neutrophils are key to the progression of the illness[7].

Neutrophils are granulocytes that have a characteristic multilobed nucleus, usually ranging from 3 to 5 interconnected lobes[8]. They combat pathogens in a non-specific way, as they take part in innate immune system[7]. After neutrophils migrate toward sites of infection or inflammation via chemotaxis, they help amplify inflammatory reactions by recruiting and activating other cells of the immune system and attack micro-organisms by phagocytosis, degranulation or neutrophil extracellular traps[9].

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[1] World Health Organization (2019, 2 August). Fact sheets: Pneumonia.

[2] Sharma S, Maycher B, Eschun G (May 2007). “Radiological imaging in pneumonia: recent innovations”. Current Opinion in Pulmonary Medicine. 13 (3): 159–69.

[3] Ruuskanen O, Lahti E, Jennings LC, Murdoch DR (April 2011). “Viral pneumonia”. Lancet. 377 (9773): 1264–75

[4] Figueiredo LT (September 2009). “Viral pneumonia: epidemiological, clinical, pathophysiological and therapeutic aspects”. Jornal Brasileiro de Pneumologia. 35 (9): 899–906

[5] World Health Organization (2020, 3 March). Rolling updates on coronavirus disease (COVID-19).

[6] Fleisher, Gary R.; Ludwig, Stephen, eds. (2010). Textbook of pediatric emergency medicine (6th ed.). Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins Health. p. 914

[7] Balamayooran, G., Batra, S., Fessler, M. B., Happel, K. I., & Jeyaseelan, S. (2010). Mechanisms of neutrophil accumulation in the lungs against bacteria. American journal of respiratory cell and molecular biology, 43(1), 5–16. https://doi.org/10.1165/rcmb.2009-0047TR

[8] Veda, P. (2011). Why are Neutrophils Polymorphonuclear? European Journal of Inflammation, 85–93.

[9] Selders, G. S., Fetz, A. E., Radic, M. Z., & Bowlin, G. L. (2017). An overview of the role of neutrophils in innate immunity, inflammation and host-biomaterial integration. Regenerative biomaterials, 4(1), 55–68. https://doi.org/10.1093/rb/rbw041

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