Postdoc Indiana Univ. Sch. of Med. Indianapolis, Indiana, United States
Disclosure(s):
Raj Priya, PhD: No financial relationships to disclose
Introduction/Rationale: Lyme disease, caused by Borrelia burgdorferi (B. burgdorferi), is shaped by complex interactions between innate & adaptive immunity. Previous studies show that B. burgdorferi activates cGAS–STING in macrophages by utilizing c-di-AMP as a PAMP, leading to type I interferon production. Building on this, we aimed to define the role of cGAS-STING signaling in coordinating crucial cell-to-cell crosstalk during the early stage of B. burgdorferi infection.
Methods: We used in vitro & ex vivo co-culture model to assess NK cell activation (IFN-γ production, CD69 expression & LDH release) following stimulation with B. burgdorferi-infected wild-type & cGAS-/- or STING-/- macrophages, neutrophils, or their supernatants. Phagocytosis & IFNAR blocking were performed to determine the mechanism of NK cell activation. Finally, we utilized cGAS-/-, STING-/-, IFNAR-/- & NK cell depletion mouse models to assess B. burgdorferi burden & dissemination.
Results: Macrophage-intrinsic cGAS–STING signaling, but not that of neutrophils, was essential for NK cell activation & subsequent IFN-γ production. Inhibition of cGAS–STING signaling in macrophages significantly reduced NK cell responses in co-cultures. This effect was largely dependent on macrophage phagocytic activity & mediated by macrophage-derived IFN-I. Blocking IFNAR on NK cells impaired their activation in response to the infected macrophage supernatant, confirming a required role for IFN-I signaling. Consistently, STING agonist treatment of macrophages enhanced NK cell activation, whereas direct stimulation of NK cells with STING agonist or B. burgdorferi failed to do so. In vivo, IFNAR deficiency or NK cell depletion significantly increased B. burgdorferi burden at the infection site, while loss of cGAS-STING signaling promoted bacterial dissemination.
Conclusion: These findings show that macrophage cGAS–STING signaling coordinates NK cell IFN-γ responses via type I IFN, establishing a critical, MyD88-independent axis for early immune control of B. burgdorferi.
