Polyphosphates attenuate interleukin-12 production in macrophages infected with Legionella pneumophila

IL-12p40 protein release was dose-dependently reduced by long-chain polyphosphates (~Pi 700), but not by short-chain, mammalian-type polyphosphates (Pi 70), indicating a specific bacterial mechanism targeting innate immune signaling. In contrast, IL-18, processed by inflammasome activation and synergizing functionally with IL-12, was not consistently suppressed. Polyphosphates predominantly inhibited LPS/TLR4 signaling, with Legionella-induced IL-12 relying on the MyD88 pathway, but not TRIF.

RAGE and P2Y1, previously implicated in polyphosphate biology, were not required for IL-12 suppression. However, PI3K/AKT signaling appeared to mediate polyphosphate effects, which were reversed by the PI3K inhibitors, LY294002, copanlisib and eganelisib. Finally, long-chain polyphosphates suppressed IL-12 release also from human monocyte-derived macrophages exposed to L. pneumophila or LPS.

In summary, our findings identify a selective inhibition of IL-12 by long-chain bacterial polyphosphates, suggesting that these molecules act as bacterial effectors capable of suppressing protective innate immune responses.