Cytokines are inflammatory proteins that play a crucial role in an inflammatory response. But a response that is too strong is characterised as a "cytokine storm", which can also be harmful for the patient. It was previously thought that a cytokine storm was responsible for a severe immune response to COVID-19, but researchers compared several cytokine levels of patients with COVID-19 to patients with other diseases and found no increase in cytokine concentration. This indicates to the fact that severe COVID-19 immune responses are not liked to a cytokine storm. The cytokines that were tested were TNF-alpha, IL-6 and IL-8. It was found that the concentration of these cytokines in COVID-19 patients was significantly less elevated.