Borrelia burgdorferi Secretes c-di-AMP as an Extracellular Pathogen-Associated Molecular Pattern to Elicit Type I Interferon Responses in Mammalian Hosts

Borrelia burgdorferi (B. burgdorferi), an extracellular spirochetal pathogen, elicits a type-I interferon (IFN-I) response that contributes to the pathology of Lyme disease, including the development and severity of Lyme arthritis. However, the specific Pathogen-Associated Molecular Patterns (PAMPs) of B. burgdorferi responsible for triggering the IFN-I response are not well understood. Previous studies have identified an unknown, nuclease-resistant component in B. burgdorferi culture supernatants that significantly stimulates the IFN-I response, but its identity remains unknown. In this study, we reveal that B. burgdorferi secretes cyclic-di-adenosine monophosphate (c-di-AMP) as a key extracellular PAMP, inducing the host IFN-I response in macrophages. Using genetically manipulated B. burgdorferi strains, we demonstrate a requirement of c-di-AMP for stimulating IFN-I response by macrophages ex vivo. Additionally, infecting mice with B. burgdorferi alongside exogenous c-di-AMP resulted in a markedly increased IFN-I response in mouse tissues. Furthermore, inactivation or inhibition of the host STING signaling pathway significantly reduced the IFN-I response, indicating that c-di-AMP-induced IFN-I production is STING-dependent. Our findings identify c-di-AMP as a crucial PAMP secreted by B. burgdorferi to elicit the host IFN-I response via activation of STING signaling pathway, suggesting that targeting c-di-AMP production could represent a novel therapeutic strategy against Lyme arthritis. SUMMARYBorrelia burgdorferi, the bacteria that causes Lyme disease, induces a robust host immune response, including the production of type-I interferon (IFN-I). While this response helps combat the infection, it also contributes to complications such as Lyme arthritis. Our research aimed to identify the specific bacterial component that triggers the IFN-I response. We discovered that Borrelia burgdorferi releases a second messenger molecule, cyclic-di-adenosine monophosphate (c-di-AMP), which is recognized by host immune cells and subsequently triggers IFN-I production. This finding is significant as it advances our understanding of Lyme disease pathogenesis and offers a new strategy to tackle Lyme disease by targeting the production of c-di-AMP, in which we may be able to reduce the severity of the disease and mitigate long-term tissue damage. One sentence summaryBorrelia burgdorferi c-di-AMP induces Type I IFN response