Faulty Assassins

Natural killer (NK) cells, like the one shown, live up to their name. During a viral infection, these specialised immune cells identify compromised host cells and deploy toxic granules (magenta) to obliterate them. In a rare but sometimes fatal autoinflammatory disorder called mevalonate kinase deficiency (MKD), however, NK cells fail to properly deliver the poison. As the viral infection rages on, these faulty NK cells call for back up – secreting the cytokine IFN-gamma to recruit other immune cells – which sends inflammation into overdrive. Even without infections, patients with MKD suffer regular inflammatory flare ups and traditional anti-inflammatories aren’t always effective. Recently, in light of the NK cell findings, an IFN-gamma inhibitor called baricitinib (used to treat other autoimmune disorders) was given to a severely ill infant with MKD. While the child ultimately succumbed to the illness, the drug did significantly reduce their inflammation, suggesting it might help other MKD patients.

Written by Ruth Williams

Ruth Williams

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Ruth is a freelance science journalist based in the US. She's a regular correspondent for The Scientist, and her work has appeared in The Lancet, Nature, Scientific American Mind, BBC Focus and elsewhere. Twitter @rooph

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• Image by James Cremasco, Garvan Institute, re work by Marcia A. Munoz, Iona S. Schuster & James Cremasco, and colleagues
• Garvan Institute of Medical Research, Darlinghurst, NSW, Australia
• Image originally published with a Creative Commons Attribution 4.0 International (CC BY 4.0)
• Research published in Immunity, May 2026