Samuel, J. E. | Search bioRxiv

bioRxiv2026

Coxiella burnetii type IVB secretion system modulates TLR3/TRIF-dependent NF-κB and IRF responses during infection

Coxiella burnetii ( Cb ), the causative agent of Q fever, replicates within host macrophages by modulating innate immune responses through its type IVB secretion system (T4SS). Host cells sense pathogens via Pattern recognition receptors (PRRs), including Toll-like receptors (TLRs), to recognize pathogen-associated molecular patterns (PAMPs) and initiate signaling pathways that drive pro-inflammatory cytokine and interferon responses. Toll-like receptor 3 (TLR3) triggers the nuclear translocation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-{kappa}B) and Interferon regulatory factors (IRFs) resulting in pro-inflammatory cytokine production and type I interferon (IFN-I) induction. Here we demonstrate that Cb requires T4SS to suppress TLR3-induced NF-{kappa}B and IRF transcriptional responses. Furthermore, RNA purified from both virulent and avirulent Cb is sufficient to activate TLR3, identifying pathogen RNA as a relevant PAMP in this context. Using a pulmonary infection model with virulent Cb, we found that TLR3/ Toll-Interleukin-1 Receptor Domain-Containing Adapter Protein Inducing Interferon Beta (TRIF)-dependent innate immune pathway inhibits cachexia. In contrast, signaling through the interferon-/{beta} receptor (IFNAR) restricts bacterial dissemination, indicating that these pathways play distinct but complementary roles in host defense. Mechanistically, Cb suppresses TLR3/TRIF signaling in a T4SS-dependent manner by preventing host TLR3 recruitment to the Coxiella-containing vacuole (CCV) and disrupting TRIF-TNF Receptor-Associated Factor 6 (TRAF6) interactions, thereby selectively inhibiting impairing NF-{kappa}B activation. Consistent with this, we identify five T4SS effector proteins that attenuate TLR3-induced NF-{kappa}B signaling, including CBU1292, which suppresses both NF-{kappa}B and IRF-dependent responses downstream of TLR3.

microbiology↗

bioRxiv2024

Molecular Mechanisms of Coxiella burnetii Formalin Fixed Cellular Vaccine Reactogenicity Evaluated in an Established Mouse Model

Local and systemic reactogenic responses to Q-VAX(R) have prevented licensing of this vaccine outside of Australia. These reactogenic responses occur in previously sensitize individuals and have not been well defined at the cellular level, in part because many studies have been done in guinea pigs that have limited molecular tools. We previously characterized a mouse model of reactogenicity where local reactions sites showed an influx of CD8+ and IFN{gamma}-expressing IL17a+ CD4+ T cells consistent with a Th1 delayed-type hypersensitivity. In this study we determined using depletion and adoptive transfer experiments that both anti-Coxiella antibodies and CD4+ T cells were essential for localized reactions at the site of vaccination. Furthermore, IFN{gamma} depletion showed significant histological changes at the local reaction sites demonstrating the essential nature of this cytokine to reactogenicity. In addition to the cells and cytokines required for this response, we determined WCV material remained at the site of vaccination for at least 26 weeks post-injection. Transmission electron microscopy of these sites demonstrated intact rod-shaped bacteria at 2 weeks post-injection and partially degraded bacteria within macrophages at 26 weeks post-injection. Finally, since SCVs are an environmentally stable form, we determined that local reactions were more severe when the WCV material was prepared with higher levels of SCVs compared to typical WCV or with higher levels of LCV. These studies support the hypothesis that antigen persistence at the site of injection contributes to this reactogenicity and that anti-Coxiella antibodies, CD4+ T cells, and IFN{gamma} each contribute to this process.

immunology↗