CALHM6 is an immunological synapse ion channel required for macrophage-natural killer cell communication upon bacterial infection

Membrane ion channels of the calcium homeostasis modulator (CALHM) family promote cell-cell crosstalk at synapses via ATP release, where ATP acts as a neurotransmitter. CALHM6, the only CALHM highly expressed in immune cells, has been linked to induction of natural killer (NK) cell anti-tumour activity. Its mechanism of action and broader functions in the immune system are, however, unclear.  Here we generated Calhm6^-/- mice and report that CALHM6 is important for regulating the early innate control of Listeria monocytogenes infection in vivo. We find that CALHM6 is upregulated in macrophages by pathogen-derived signals, and that it relocates from intracellular compartment to the macrophage-NK cell synapse, facilitating ATP release and controlling the kinetics of NK cell activation. Anti-inflammatory cytokines terminate CALHM6 expression. CALHM6 forms an ion channel when expressed in the plasma membrane of Xenopus oocytes, where channel opening is controlled by a conserved acidic residue, E119, but CALHM6 is localized to intracellular compartments in mammalian cells. Our results contribute to understanding of neurotransmitter-like signal exchange between immune cells that fine-tunes the timing of innate immune responses.