Researchers at the Paul-Ehrlich-Institut, in collaboration with the Freiburg University Medical Center, have gained new insights into why certain influenza A viruses cause more severe illness than others. The study, published in the online edition of Emerging Microbes & Infections on 03.09.2025, examined eleven different influenza A virus strains and their effects on human immune cells.

The results show that highly pathogenic bird flu viruses infect certain immune cells and thereby stimulate the production of type I interferon. This could explain why these viruses often cause more dangerous courses of the disease. While plasmacytoid dendritic cells produce large amounts of the antiviral messenger interferon α in all influenza viruses, highly pathogenic viruses also infect myeloid dendritic cells and macrophages. This infection leads to increased interferon α production, which can trigger a cytokine storm – an excessive immune response that damages the tissue more than the virus itself.

The findings provide important approaches to better understand the mechanisms of severe flu courses and to develop targeted therapies and protective measures for risk groups. Highly pathogenic influenza viruses in particular, which are often transmitted from birds to humans, are associated with high mortality rates and often cause severe pneumonia and even acute lung failure.

The study emphasizes the key role of virus replication in certain immune cells as a trigger for dangerous immune reactions. In the long term, these findings could help to better assess dangerous virus variants and develop new treatment approaches.

Original Paper:

Full article: Influenza A virus induced interferon-alpha production by myeloid dendritic cells and macrophages requires productive infection

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New insights into cell entry of influenza viruses – MedLabPortal

Editor: X-Press Journalistenbüro GbR

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