Based on previous studies of the COVID-19 pandemic, it is known that a specific form of white immune cells, natural killer (NK) cells, make an important contribution to the early antiviral immune response against SARS-CoV-2. An international team led by the University of Bonn has now found that in severe courses of COVID-19, the ability of natural killer cells to prevent pathological proliferation of fibrous tissue in the lungs is often impaired. Major parts of the study were conducted at the University Hospital Bonn and the German Center for Neurodegenerative Diseases (DZNE). The results have been published online in advance in the reputed journal Immunity. The print version will appear shortly.