Coxiella burnetii lipopolysaccharide blocks p38α-MAPK activation through the disruption of TLR-2 and TLR-4 association

Susceptibility, Immunity, and Persistent Infection Drive Endemic Cycles of Coxiellosis on Dairy Farms

Coxiella (C.) burnetii, a zoonotic bacterium, is prevalent in dairy farms. Some cows develop a persistent infection and shed C. burnetii into milk and occasionally by amniotic fluid at calving. Serological diagnosis of Q fever in humans is performed by phase (Ph)-specific antibody tests; PhII antibodies usually indicate an acute infection, while the development of a chronic infection is characterised by elevated PhI antibody titres. Phase-specific tests have now been established for diagnosis of coxiellosis in cattle. Additionally, an interferon-γ (IFN-γ) recall assay has been implemented to assess cellular immunity to C. burnetii in cattle. Milk samples from all lactating cows (n = 2718) of 49 Bavarian dairy farms were collected through a convenience sample and analysed for phase-specific antibodies. Antibody profiles were evaluated by age. Based on the seropositivity of first-lactation cows, three distinct herd profiles were observed: an 'acute' state of herd infection was characterised by a PhI-/PhII+ pattern. The detection of PhI antibodies (PhI+/PhII+) characterised the 'chronic' state, and seronegative results defined the 'silent' state of herd infection. If antibodies had not been detected in multiparous cows, the herd was considered as probably free of coxiellosis. The analysed cattle herds were noted to have an 'acute' (n = 12, 24.5%), 'chronic' (n = 18, 36.8%), or 'silent' state of herd infection (n = 16, 32.6%). Only three farms (6.1%) were classified as 'free' of C. burnetii. The detection of these herd states over a time period of 4 years in one farm indicated that the described states occur in a cyclical manner. Frequently, a wave-like profile was seen, i.e., a circumscribed seronegative age group was flanked by seropositive age groups. In seronegative animals, IFN-γ reactivity was demonstrated. Seroconversion after vaccination was observed by day 7 post-vaccination in chronically infected herds, whereas in the case of silent infection, it started by day 14. These data indicated a pre-existing immunity in seronegative animals in chronically infected herds. Additionally, IFN-γ reactivity was detected in seronegative calves (>3 months) and heifers from chronically infected farms compared to a negative farm. An infection prior to 3 months of age resulted in cellular immunity in the absence of detectable antibodies. An infection around calving would explain this. The aforementioned circumscribed seronegative age groups are, therefore, explained by an infection early in life during active shedding at calving. Based on these results, an endemic cycle of coxiellosis is proposed: Susceptible young heifers get infected by persistently infected cows. Subsequently, shedding of C. burnetii at calving results in infection and then in cellular immunity in offspring. When these calves enter the cow herd two years later, a maximum of herd immunity is achieved, shedding ceases, and new susceptible animals are raised. In an acutely infected dairy farm, the PhI+/PhII+ serological pattern prevailed in second-lactation cows. In this study, stored sera collected since birth were analysed retrospectively. From the earliest seroconversion, the peak of seroconversion took about 33 months. These data suggested a slow spread of infection within herds. The classification of dairy cow herds is a promising basis for further analysis of the clinical impact of coxiellosis.

Drosophila melanogaster Sting mediates Coxiella burnetii infection by reducing accumulation of reactive oxygen species

The Gram-negative bacterium Coxiella burnetii is the causative agent of query fever in humans and coxiellosis in livestock. C. burnetii infects a variety of cell types, tissues, and animal species including mammals and arthropods, but there is much left to be understood about the molecular mechanisms at play during infection in distinct species. Human stimulator of interferon genes (STING) induces an innate immune response through the induction of type I interferons (IFNs), and IFN promotes or suppresses C. burnetii replication, depending on tissue type. Drosophila melanogaster contains a functional STING ortholog (Sting) which activates NF-κB signaling and autophagy. Here, we sought to address the role of D. melanogaster Sting during C. burnetii infection to uncover how Sting regulates C. burnetii infection in flies. We show that Sting-null flies exhibit higher mortality and reduced induction of antimicrobial peptides following C. burnetii infection compared to control flies. Additionally, Sting-null flies induce lower levels of oxidative stress genes during infection, but the provision of N-acetyl-cysteine (NAC) in food rescues Sting-null host survival. Lastly, we find that reactive oxygen species levels during C. burnetii infection are higher in Drosophila S2 cells knocked down for Sting compared to control cells. Our results show that at the host level, NAC provides protection against C. burnetii infection in the absence of Sting, thus establishing a role for Sting in protection against oxidative stress during C. burnetii infection.

Multivalent vaccines demonstrate immunogenicity and protect against Coxiella burnetii aerosol challenge

Vaccines are among the most cost-effective public health measures for controlling infectious diseases. Coxiella burnetii is the etiological agent of Q fever, a disease with a wide clinical spectrum that ranges from mild symptoms, such as fever and fatigue, to more severe disease, such as pneumonia and endocarditis. The formalin-inactivated whole-cell vaccine Q-VAX® contains hundreds of antigens and confers lifelong protection in humans, but prior sensitization from infection or vaccination can result in deleterious reactogenic responses to vaccination. Consequently, there is great interest in developing non-reactogenic alternatives based on adjuvanted recombinant proteins. In this study, we aimed to develop a multivalent vaccine that conferred protection with reduced reactogenicity. We hypothesized that a multivalent vaccine consisting of multiple antigens would be more immunogenic and protective than a monovalent vaccine owing to the large number of potential protective antigens in the C. burnetii proteome. To address this, we identified immunogenic T and B cell antigens, and selected proteins were purified to evaluate with a combination adjuvant (IVAX-1), with or without C. burnetii lipopolysaccharide (LPS) in immunogenicity studies in vivo in mice and in a Hartley guinea pig intratracheal aerosol challenge model using C. burnetii strain NMI RSA 493. The data showed that multivalent vaccines are more immunogenic than monovalent vaccines and more closely emulate the protection achieved by Q-VAX. Although six antigens were the most immunogenic, we also discovered that multiplexing beyond four antigens introduces detectable reactogenicity, indicating that there is an upper limit to the number of antigens that can be safely included in a multivalent Q-fever vaccine. C. burnetii LPS also demonstrates efficacy as a vaccine antigen in conferring protection in an otherwise monovalent vaccine formulation, suggesting that its addition in multivalent vaccines, as demonstrated by a quadrivalent formulation, would improve protective responses.

Primary Murine Macrophages as a Tool for Virulence Factor Discovery in Coxiella burnetii

Coxiella burnetii requires a type IVB secretion system (T4SS) to promote intracellular replication and virulence. We hypothesized that Coxiella employs its T4SS to secrete effectors that enable stealthy colonization of immune cells. To address this, we used RNA sequencing to compare the transcriptional response of murine bone marrow-derived macrophages (BMDM) infected with those of wild-type Coxiella and a T4SS-null mutant at 8 and 24 h postinfection. We found a T4SS-independent upregulation of proinflammatory transcripts which was consistent with a proinflammatory polarization phenotype. Despite this, infected BMDM failed to completely polarize, as evidenced by modest surface expression of CD38 and CD11c, nitrate production, and reduced proinflammatory cytokine and chemokine secretion compared to positive controls. As these BMDM permitted replication of C. burnetii, we employed them to identify T4SS effectors that are essential in the specific cellular context of a primary macrophage. We found five Himar1 transposon mutants in T4SS effectors that had a replication defect in BMDM but not J774A.1 cells. The mutants were also attenuated in a SCID mouse model of infection. Among these candidate virulence factors, we found that CBU1639 contributed to the inhibition of macrophage proinflammatory responses to Coxiella infection. These data demonstrate that while T4SS is dispensable for the stealthy invasion of primary macrophages, Coxiella has evolved multiple T4SS effectors that specifically target macrophage function to proliferate within that specific cellular context. IMPORTANCE Coxiella burnetii, the causative agent of Q fever, preferentially infects macrophages of the respiratory tract when causing human disease. This work describes how primary macrophages respond to C. burnetii at the earliest stages of infection, before bacterial replication. We found that while infected macrophages increase expression of proinflammatory genes after bacterial entry, they fail to activate the accompanying antibacterial functions that might ultimately control the infection. This disconnect between initial response and downstream function was not mediated by the bacterium's type IVB secretion system, suggesting that Coxiella has other virulence factors that dampen host responses early in the infection process. Nevertheless, we were able to identify several type IVB secreted effectors that were specifically required for survival in macrophages and mice. This work is the first to identify type IVB secretion effectors that are specifically required for infection and replication within primary macrophages.

Natural Exposure- and Vaccination-Induced Profiles of Ex Vivo Whole Blood Cytokine Responses to Coxiella burnetii

Q fever is a zoonotic disease caused by the highly infectious Gram-negative coccobacillus, Coxiella burnetii (C. burnetii). The Q fever vaccine Q-VAX® is characterised by high reactogenicity, requiring individuals to be pre-screened for prior exposure before vaccination. To date it remains unclear whether vaccine side effects in pre-exposed individuals are associated with pre-existing adaptive immune responses to C. burnetii or are also a function of innate responses to Q-VAX®. In the current study, we measured innate and adaptive cytokine responses to C. burnetii and compared these among individuals with different pre-exposure status. Three groups were included: n=98 Dutch blood bank donors with unknown exposure status, n=95 Dutch village inhabitants with known natural exposure status to C. burnetii during the Dutch Q fever outbreak of 2007-2010, and n=96 Australian students receiving Q-VAX® vaccination in 2021. Whole blood cytokine responses following ex vivo stimulation with heat-killed C. burnetii were assessed for IFNγ, IL-2, IL-6, IL-10, TNFα, IL-1β, IP-10, MIP-1α and IL-8. Serological data were collected for all three cohorts, as well as data on skin test and self-reported vaccine side effects and clinical symptoms during past infection. IFNγ, IP-10 and IL-2 responses were strongly elevated in individuals with prior C. burnetii antigen exposure, whether through infection or vaccination, while IL-1β, IL-6 and TNFα responses were slightly increased in naturally exposed individuals only. High dimensional analysis of the cytokine data identified four clusters of individuals with distinct cytokine response signatures. The cluster with the highest levels of adaptive cytokines and antibodies comprised solely individuals with prior exposure to C. burnetii, while another cluster was characterized by high innate cytokine production and an absence of C. burnetii-induced IP-10 production paired with high baseline IP-10 levels. Prior exposure status was partially associated with these signatures, but could not be clearly assigned to a single cytokine response signature. Overall, Q-VAX® vaccination and natural C. burnetii infection were associated with comparable cytokine response signatures, largely driven by adaptive cytokine responses. Neither individual innate and adaptive cytokine responses nor response signatures were associated retrospectively with clinical symptoms during infection or prospectively with side effects post-vaccination.

Recent Advances on the Innate Immune Response to Coxiella burnetii

Coxiella burnetii is an obligate intracellular Gram-negative bacterium and the causative agent of a worldwide zoonosis known as Q fever. The pathogen invades monocytes and macrophages, replicating within acidic phagolysosomes and evading host defenses through different immune evasion strategies that are mainly associated with the structure of its lipopolysaccharide. The main transmission routes are aerosols and ingestion of fomites from infected animals. The innate immune system provides the first host defense against the microorganism, and it is crucial to direct the infection towards a self-limiting respiratory disease or the chronic form. This review reports the advances in understanding the mechanisms of innate immunity acting during C. burnetii infection and the strategies that pathogen put in place to infect the host cells and to modify the expression of specific host cell genes in order to subvert cellular processes. The mechanisms through which different cell types with different genetic backgrounds are differently susceptible to C. burnetii intracellular growth are discussed. The subsets of cytokines induced following C. burnetii infection as well as the pathogen influence on an inflammasome-mediated response are also described. Finally, we discuss the use of animal experimental systems for studying the innate immune response against C. burnetii and discovering novel methods for prevention and treatment of disease in humans and livestock.

Protective Effects of Lactobacillus plantarum Lac16 on Clostridium perfringens Infection-Associated Injury in IPEC-J2 Cells

Clostridium perfringens (C. perfringens) causes intestinal injury through overgrowth and the secretion of multiple toxins, leading to diarrhea and necrotic enteritis in animals, including pigs, chickens, and sheep. This study aimed to investigate the protective effects of Lactobacillus plantarum (L. plantarum) Lac16 on C. perfringens infection-associated injury in intestinal porcine epithelial cell line (IPEC-J2). The results showed that L. plantarum Lac16 significantly inhibited the growth of C. perfringens, which was accompanied by a decrease in pH levels. In addition, L. plantarum Lac16 significantly elevated the mRNA expression levels of host defense peptides (HDPs) in IPEC-J2 cells, decreased the adhesion of C. perfringens to IPEC-J2 cells, and attenuated C. perfringens-induced cellular cytotoxicity and intestinal barrier damage. Furthermore, L. plantarum Lac16 significantly suppressed C. perfringens-induced gene expressions of proinflammatory cytokines and pattern recognition receptors (PRRs) in IPEC-J2 cells. Moreover, L. plantarum Lac16 preincubation effectively inhibited the phosphorylation of p65 caused by C. perfringens infection. Collectively, probiotic L. plantarum Lac16 exerts protective effects against C. perfringens infection-associated injury in IPEC-J2 cells.

Undercover Agents of Infection: The Stealth Strategies of T4SS-Equipped Bacterial Pathogens

Intracellular bacterial pathogens establish their replicative niches within membrane-encompassed compartments, called vacuoles. A subset of these bacteria uses a nanochannel called the type 4 secretion system (T4SS) to inject effector proteins that subvert the host cell machinery and drive the biogenesis of these compartments. These bacteria have also developed sophisticated ways of altering the innate immune sensing and response of their host cells, which allow them to cause long-lasting infections and chronic diseases. This review covers the mechanisms employed by intravacuolar pathogens to escape innate immune sensing and how Type 4-secreted bacterial effectors manipulate host cell mechanisms to allow the persistence of bacteria.

Effect of algae or fish oil supplementation and porcine maternal stress on the adrenal transcriptome of male offspring fed a low-quality protein diet

Offspring adrenal function may be negatively affected in utero by maternal stressors such as microbial infection. Maternal supplementation with immunomodulatory compounds such as omega-3 polyunsaturated fatty acids (n-3 PUFA) may help minimize the adverse effects of maternal stress on fetal hypothalamic-pituitary-adrenal development and improve offspring health. Presently, n-3 PUFA sources are primarily fish-based, but n-3 PUFA microalgae (AL) may be an alternative. Previously, it was determined that maternal AL or fish oil (FO) supplementation to sows, in addition to maternal stress induced by Escherichia coli lipopolysaccharide (LPS) challenge appeared to have a greater influence on the stress response of male offspring compared to females. To further elaborate on these findings, this study assessed the effects of maternal AL or FO supplementation combined with a maternal LPS challenge on adrenal gene expression in male offspring fed a nursery diet containing low-quality protein sources. Forty-eight sows were fed gestation diets starting on gestation day (gd) 75 containing either 3.12% AL, 3.1% FO, or a control diet containing 1.89% corn oil. On gd 112, half the sows in each treatment were administered 10 ​μg/kg LPS i.m. Piglets were weaned at 21 days of age onto a common low-quality plant-based protein diet, and one week after weaning, four piglets per sow were administered 40 ​μg/kg LPS i.m. Two hours later, the piglets were euthanized to obtain adrenal tissue, and total RNA was extracted to carry out transcriptome analysis using the Affymetrix GeneChip WT Plus assay and subsequent validation by real-time PCR. Analysis revealed that adrenal steroidogenesis, fatty acid metabolism and immune function were significantly influenced by maternal diet and stress. Increased expression of immune-related genes including lymphocyte antigen 96, TLR-2 and NF-κB suggests that maternal AL supplementation may increase offspring sensitivity to inflammation after weaning. Decreased expression of lymphocyte antigen 96 in male offspring from sows receiving maternal LPS challenge also suggests a possible role of maternal stress in diminishing the offspring immune response to immune stress challenge. Increased expression of the genes encoding the 11BHSD2 enzyme in offspring from sows fed FO may also reduce the magnitude of the stress response. These data provide insight to the immune and metabolic mechanisms that may be influenced by maternal diet and stress.

•

Expression of adrenal steroidogenesis genes were influenced by maternal treatment.

•

Expression of lipid metabolism genes and immune function genes were enriched.

•

Maternal algae supplementation may increase offspring sensitivity to inflammation.

•

Maternal stress may reduce the offspring immune response to immune challenges.

•

Maternal fish oil supplementation may reduce the offspring stress response.

aYAP modRNA reduces cardiac inflammation and hypertrophy in a murine ischemia-reperfusion model

Myocardial recovery from ischemia-reperfusion (IR) is shaped by the interaction of many signaling pathways and tissue repair processes, including the innate immune response. We and others previously showed that sustained expression of the transcriptional co-activator yes-associated protein (YAP) improves survival and myocardial outcome after myocardial infarction. Here, we asked whether transient YAP expression would improve myocardial outcome after IR injury. After IR, we transiently activated YAP in the myocardium with modified mRNA encoding a constitutively active form of YAP (aYAP modRNA). Histological studies 2 d after IR showed that aYAP modRNA reduced cardiomyocyte (CM) necrosis and neutrophil infiltration. 4 wk after IR, aYAP modRNA-treated mice had better heart function as well as reduced scar size and hypertrophic remodeling. In cultured neonatal and adult CMs, YAP attenuated H2O2- or LPS-induced CM necrosis. TLR signaling pathway components important for innate immune responses were suppressed by YAP/TEAD1. In summary, our findings demonstrate that aYAP modRNA treatment reduces CM necrosis, cardiac inflammation, and hypertrophic remodeling after IR stress.

"Hairiness" is a Facsimile of Reorganized Cytoskeletons: A Cytopathic Effect of Coxiella burnetii

In 1993, I reported that Coxiella burnetii transforms human B cells into hairy cells (cbHCs), the first hairy cell reported outside of hairy cell leukemia (HCL). Over last few decades, advances in molecular biology have provided evidence supporting that C. burnetii induces hairiness and inhibits the apoptosis of host cells. The present review summarizes new information in support of cbHC. C. burnetii was shown to induce reorganization of the cytoskeleton and to inhibit apoptosis in host cells. Peritoneal B1a cells were found to be permissive for virulent C. burnetii Nine Mile phase I (NMI) strains in mice. C. burnetii severely impaired E-cad expression in circulating cells of Q fever patients. B-cell non-Hodgkin lymphoma was linked to C. burnetii. Mutation of BRAF V600E was pronounced in HCL, but "hairiness" was not linked to the mutation. Risk factors shared among coxiellosis and HCL in humans and animals were reported in patients with Q-fever. Accordingly, I propose that C. burnetii induces reorganization of the cytoskeleton and inhibits apoptosis as cytopathic effects that are not target cell specific. The observed hairiness in cbHC appears to be a fixed image of dynamic nature, and hairy cells in HCL are distinct among lymphoid cells in circulation. As the cytoskeleton plays key roles in maintaining cell structural integrity in health and disease, the pathophysiology of similar cytopathic effects should be addressed in other diseases, such as myopathies, B-cell dyscrasias, and autoimmune syndromes.

Mast Cell Cytonemes as a Defense Mechanism against Coxiella burnetii

Mast cells (MCs) are found in tissues that are in close contact with external environment, such as skin, lungs, or intestinal mucosa but also in the placenta during pregnancy. If their role in mediating allergic conditions is established, several studies now highlight their importance during infection with extracellular pathogens. This study showed a new and effective antimicrobial mechanism of MCs against Coxiella burnetii, an intracellular bacterium whose infection during pregnancy is associated with abortion, preterm labor, and stillbirth. The data reveal that in response to C. burnetii, MCs release extracellular actin filaments that contain antimicrobial agents and are capable to trap and kill bacteria. We show that this mechanism is dependent on the cooperation of two membrane receptors, CD36 and Toll-like receptor 4, and may occur in the placenta during pregnancy by using ex vivo placental MCs. Overall, this study reports an unexpected role for MCs during infection with intracellular bacteria and suggests that MC response to C. burnetii infection is a protective defense mechanism during pregnancy.

Mast cells (MCs) are critical mediators of inflammation; however, their microbicidal activity against invading pathogens remains largely unknown. Here, we describe a nonpreviously reported antibacterial mechanism used by MCs against Coxiella burnetii, the agent of Q fever. We show that C. burnetii interaction with MCs does not result in bacterial uptake but rather induces the formation of extracellular actin filaments named cytonemes. MC cytonemes express cathelicidin and neutrophil elastase and mediate the capture and destruction of entrapped bacteria. We provide evidence that MC cytoneme formation and microbicidal activity are dependent on the cooperation of the scavenger receptor CD36 and Toll-like receptor 4. Taken together, our results suggest that MCs use an extracellular sophisticated mechanism of defense to eliminate intracellular pathogens, such as C. burnetii, before their entry into host cells.

The roles of the TLR/NF‑κB signaling pathway in the mutual interactions between the lung and the large intestine

The 'exterior-interior relationship between the lung and the large intestine' is a classical basic theory in Traditional Chinese Medicine. The present study aimed to investigate the roles of the toll like receptor/nuclear factor‑κB (TLR/NF‑κB) signaling pathway in the mutual interactions between the lung and the large intestine. A rat model of allergic asthma complicated with intestinal flora disorder was established by oral administration of Candida albicans and intraperitoneal injection with ovalbumin. The number of inflammatory cells and expression levels immunoglobulin (Ig)E, secretory IgA, interleukin (IL)‑4 and interferon‑γ in serum and bronchoalveolar lavage fluid were subsequently measured. Bacterial colonies and expression of 16S ribosomal DNA were studied in feces samples and pathological alterations of lung tissues were identified. Furthermore, the expression levels of genes associated with the TLR/NF‑κB signaling pathway in the lung and intestinal tissues were determined by reverse transcription‑quantitative polymerase chain reaction. The results of the present study indicated that, in the rat model of allergic asthma complicated with intestinal flora disorder, the expression levels of IL‑4 and IgE, and the numbers of inflammatory cells and C. albicans increased, and marked inflammatory cell infiltration was observed in lung tissues, suggesting that the animal model was successfully established. Furthermore, the present results revealed the mRNA expression levels of genes associated with the TLR/NF‑κB signaling (including myeloid differentiation primary response 88, TNF receptor associated factor 6 and β‑arrestin) were upregulated in both of the lung and intestinal tissues of the model group rats. Collectively, the results demonstrated that the TLR/NF‑κB signaling may serve roles in the mutual interactions between the lung and the large intestine, and TLR and NF‑κB may be potential targets for the treatment of lung diseases complicated with intestinal disorders.

Coxiella burnetii Lipopolysaccharide: What Do We Know?

A small gram-negative bacterium, Coxiella burnetii (C. burnetii), is responsible for a zoonosis called Q fever. C. burnetii is an intracellular bacterium that can survive inside microbicidal cells like monocytes and macrophages by hijacking several functions of the immune system. Among several virulence factors, the lipopolysaccharide (LPS) of C. burnetii is one of the major factors involved in this immune hijacking because of its atypical composition and structure. Thus, the aim of this mini-review is to summarize the repressive effects of C. burnetii LPS on the antibacterial immunity of cells.

From Q Fever to Coxiella burnetii Infection: a Paradigm Change

Coxiella burnetii is the agent of Q fever, or "query fever," a zoonosis first described in Australia in 1937. Since this first description, knowledge about this pathogen and its associated infections has increased dramatically. We review here all the progress made over the last 20 years on this topic. C. burnetii is classically a strict intracellular, Gram-negative bacterium. However, a major step in the characterization of this pathogen was achieved by the establishment of its axenic culture. C. burnetii infects a wide range of animals, from arthropods to humans. The genetic determinants of virulence are now better known, thanks to the achievement of determining the genome sequences of several strains of this species and comparative genomic analyses. Q fever can be found worldwide, but the epidemiological features of this disease vary according to the geographic area considered, including situations where it is endemic or hyperendemic, and the occurrence of large epidemic outbreaks. In recent years, a major breakthrough in the understanding of the natural history of human infection with C. burnetii was the breaking of the old dichotomy between "acute" and "chronic" Q fever. The clinical presentation of C. burnetii infection depends on both the virulence of the infecting C. burnetii strain and specific risks factors in the infected patient. Moreover, no persistent infection can exist without a focus of infection. This paradigm change should allow better diagnosis and management of primary infection and long-term complications in patients with C. burnetii infection.

Analysis of the Caenorhabditis elegans innate immune response to Coxiella burnetii

The nematode Caenorhabditis elegans is well established as a system for characterization and discovery of molecular mechanisms mediating microbe-specific inducible innate immune responses to human pathogens. Coxiella burnetii is an obligate intracellular bacterium that causes a flu-like syndrome in humans (Q fever), as well as abortions in domesticated livestock, worldwide. Initially, when wild type C. elegans (N2 strain) was exposed to mCherry-expressing C. burnetii (CCB) a number of overt pathological manifestations resulted, including intestinal distension, deformed anal region and a decreased lifespan. However, nematodes fed autoclave-killed CCB did not exhibit these symptoms. Although vertebrates detect C. burnetii via TLRs, pathologies in tol-1(-) mutant nematodes were indistinguishable from N2, and indicate nematodes do not employ this orthologue for detection of C. burnetii. sek-1(-) MAP kinase mutant nematodes succumbed to infection faster, suggesting that this signaling pathway plays a role in immune activation, as previously shown for orthologues in vertebrates during a C. burnetii infection. C. elegans daf-2(-) mutants are hyper-immune and exhibited significantly reduced pathological consequences during challenge. Collectively, these results demonstrate the utility of C. elegans for studying the innate immune response against C. burnetii and could lead to discovery of novel methods for prevention and treatment of disease in humans and livestock.