According to a communication from the CNRS dated November 12, 2025. Based on a scientific publication in Nature Ecology & Evolution to which Lucie Étienne, CNRS research director at CIRI, and Alexandre Legrand, INSERM researcher and CIRI doctor, contributed: Evolutionary characterization of antiviral SAMD9/9L across kingdoms supports ancient convergence and lineage-specific adaptations. Thumbnail photo credit: © Cédric SUEUR/Marie PELE/IPHC/CNRS Images
In a study published in Nature Ecology and Evolution , scientists show that the SAMD9 and SAMD9L genes, key players in human antiviral immunity and involved in rare genetic diseases, share very strong similarities with defense systems found in bacteria. Their evolution, marked by recent losses and adaptations in mammals, sheds light on the millennia-long arms race between viruses and hosts. In some primates, these developments offer better protection against HIV replication, opening up avenues for a better understanding of the subtleties of our immunity.
Ancient genes at the heart of antiviral defenses
Intracellular innate immunity is one of the body’s first lines of defense against viruses. It relies on hundreds of proteins capable of detecting pathogens (called sensors) and/or blocking their replication, known as antiviral effectors.
Among them, the proteins encoded by the SAMD9 and SAMD9L genes play a key role in humans: they slow down the production of viral proteins, particularly those of poxviruses and lentiviruses such as HIV. A disruption of these genes, caused by genetic mutations, can lead to serious conditions such as autoimmune diseases or certain cancers.
The study published in the journal Nature Ecology and Evolution highlights the complex evolutionary history of this gene family: duplications, losses, rapid evolutions, all signs of constant selection pressures often exerted by viruses. This phenomenon illustrates a veritable evolutionary "arms race": viruses develop strategies to infect, while hosts strengthen their defenses, pushing each to evolve constantly.
From bacteria to primates, a convergent evolution of antiviral defenses
By combining genetic and structural analyses of public data from a wide range of species (bacteria, animals, including primates), scientists have been able to show that proteins similar to SAMD9 exist even in bacteria.
In the latter, these proteins, called Avs, help defend against viruses that infect bacteria (bacteriophages). Laboratory experiments have shown that when Avs9 (the most similar to SAMD9) is activated, it causes the death of the bacterium, an "altruistic suicide" that prevents the virus from spreading.
Read more on the CNRS website
Reference
Legrand A, Demeure R, Chantharath A, Rey C, Baltenneck J, Gilchrist CLM, Rocha JL, Loyer C, Picard L, Cimarelli A, Steinegger M, Rousset F, Sudmant PH, Etienne L. Evolutionary characterization of antiviral SAMD9/9L across kingdoms supports ancient convergence and lineage-specific adaptations. Nat Ecol Evol. 2025 Nov 11. DOI: 10.1038/s41559-025-02845-x
