Manipulation of the nucleotide pool in human, bacterial and plant immunity.

The cell-autonomous innate immune system is responsible for sensing and mitigating viral infection at the level of individual cells. Many of the mechanisms used by the cell-autonomous innate immune system in eukaryotic cells are ancient and have evolutionary roots in bacterial systems that defend against phage infection. Studies from recent years have shown that modification of the free nucleotide pool is central to many of these conserved immune mechanisms. In this Review, we explain how immune pathways manipulate the available pool of nucleotides to deprive viruses of molecules essential for their replication, how immune proteins chemically modify nucleotides to generate immune signalling molecules, and how cell-autonomous innate immune mechanisms produce altered nucleotides that poison viral replication. We also discuss the mechanisms used by viruses to antagonize nucleotide-based immunity. Finally, we explore the evolutionary logic of using nucleotides as building blocks for immune responses.