Coxiella burnetii is an intracellular, gram-negative bacterium that causes the zoonosis Q fever. This disease typically presents as an acute flu-like illness with persistent, focalized infections occurring less frequently. Clinical outcomes of Q fever have been associated with distinct genomic groups of C. burnetii, suggesting that gene content is responsible for virulence potential. To investigate this hypothesis, the virulence of thirteen C. burnetii strains (representing genomic groups I-VI) was evaluated in a guinea pig infection model by intraperitoneal injection. Seven strains caused a sustained fever (at least two days ≥39.5°C) in at least half of the animals within each experimental group. At fourteen days post infection, animals were euthanized and additional endpoints were evaluated, including splenomegaly and serology. The magnitude of these endpoints roughly correlated with the onset, duration, and severity of fever. The most severe disease was caused by group I strains. Intermediate and no virulence were evidenced following infection with group II-V and group VI strains, respectively. Flow cytometric analysis of the mesenteric lymph nodes revealed decreased CD4⁺ T cell frequency following infection with highly virulent group I strains. These findings buttress the hypothesis that the pathogenic potential of C. burnetii strains correlates with genomic grouping. These data, combined with comparative genomics and genetic manipulation, will improve our understanding of C. burnetii virulence determinants.

Didecyldimethylammonium chloride (DDAC) is a dialkyl-quaternary ammonium compound that is used in numerous products for its bactericidal, virucidal and fungicidal properties. There have been clinical reports of immediate and delayed hypersensitivity reactions in exposed individuals; however, the sensitization potential of DDAC has not been thoroughly investigated. The purpose of these studies was to evaluate the irritancy and sensitization potential of DDAC following dermal exposure in a murine model. DDAC induced significant irritancy (0.5 and 1%), evaluated by ear swelling in female Balb/c mice. Initial evaluation of the sensitization potential was conducted using the local lymph node assay (LLNA) at concentrations ranging from 0.0625–1%. A concentration-dependent increase in lymphocyte proliferation was observed with a calculated EC3 value of 0.17%. Dermal exposure to DDAC did not induce increased production of IgE as evaluated by phenotypic analysis of draining lymph node B-cells (IgE ⁺ B220⁺) and measurement of total serum IgE levels. Additional phenotypic analyses revealed significant and dose-responsive increases in the absolute number of B-cells, CD4 ⁺ T-cells, CD8 ⁺ T-cells and dendritic cells in the draining lymph nodes, along with significant increases in the percentage of B-cells (0.25% and 1% DDAC) at Day 10 following 4 days of dermal exposure. There was also a significant and dose-responsive increase in the number of activated CD44 ⁺ CD4 ⁺ and CD8 ⁺ T-cells and CD86 ⁺ B-cells and dendritic cells following exposure to all concentrations of DDAC. These results demonstrate the potential for development of irritation and hypersensitivity responses to DDAC following dermal exposure and raise concerns about the use of this chemical and other quaternary ammonium compounds that may elicit similar effects.

Triclosan is an antimicrobial chemical incorporated into many personal, medical and household products. Approximately, 75% of the U.S. population has detectable levels of triclosan in their urine, and although it is not typically considered a contact sensitizer, recent studies have begun to link triclosan exposure with augmented allergic disease. We examined the effects of dermal triclosan exposure on the skin and lymph nodes of mice and in a human skin model to identify mechanisms for augmenting allergic responses. Triclosan (0%–3%) was applied topically at 24-h intervals to the ear pinnae of OVA-sensitized BALB/c mice. Skin and draining lymph nodes were evaluated for cellular responses and cytokine expression over time. The effects of triclosan (0%–0.75%) on cytokine expression in a human skin tissue model were also examined. Exposure to triclosan increased the expression of TSLP, IL-1β, and TNF-α in the skin with concomitant decreases in IL-25, IL-33, and IL-1α. Similar changes in TSLP, IL1B, and IL33 expression occurred in human skin. Topical application of triclosan also increased draining lymph node cellularity consisting of activated CD86⁺GL-7⁺ B cells, CD80⁺CD86⁺ dendritic cells, GATA-3⁺OX-40⁺IL-4⁺IL-13⁺ Th2 cells and IL-17 A⁺ CD4 T cells. In vivo antibody blockade of TSLP reduced skin irritation, IL-1β expression, lymph node cellularity, and Th2 responses augmented by triclosan. Repeated dermal exposure to triclosan induces TSLP expression in skin tissue as a potential mechanism for augmenting allergic responses.

Triclosan is an antimicrobial chemical commonly used occupationally and by the general public. Using select immune function assays, the purpose of these studies was to evaluate the immunotoxicity of triclosan following dermal exposure using a murine model. Triclosan was not identified to be a sensitizer in the murine local lymph node assay (LLNA) when tested at concentrations ranging from 0.75–3.0%. Following a 28-day exposure, triclosan produced a significant increase in liver weight at concentrations of ≥ 1.5%. Exposure to the high dose (3.0%) also produced a significant increase in spleen weights and number of platelets. The absolute number of B-cells, T-cells, dendritic cells and NK cells were significantly increased in the skin draining lymph node, but not the spleen. An increase in the frequency of dendritic cells was also observed in the lymph node following exposure to 3.0% triclosan. The IgM antibody response to sheep red blood cells (SRBC) was significantly increased at 0.75% – but not at the higher concentrations – in the spleen and serum. These results demonstrate that dermal exposure to triclosan induces stimulation of the immune system in a murine model and raise concerns about potential human exposure.

Q fever is a zoonotic disease caused by the intracellular pathogen Coxiella burnetii. This disease typically manifests as a self-limiting, febrile illness known as acute Q fever. Due to the aerosol transmissibility, environmental persistence, and infectivity of C. burnetii, this pathogen is a notable bioterrorism threat. Despite extensive efforts to develop next-generation human Q fever vaccines, only one vaccine, Q-Vax®, is commercially available. Q-Vax® is a phase I whole-cell vaccine, and its licensed use is limited to Australia, presumably due to the potential for a post-vaccination hypersensitivity response. Pre-clinical Q fever vaccine development is a major area of interest, and diverse approaches have been undertaken to develop an improved Q fever vaccine. Following a brief history of Q fever vaccine development, current approaches will be discussed along with future considerations for an improved Q fever vaccine.

Coxiella burnetiiis the bacterial causative agent of the zoonosis Q fever. The current human Q fever vaccine, Q-VAX^®, is a fixed, whole cell vaccine (WCV) licensed solely for use in Australia.C. burnetiiWCV administration is associated with a dermal hypersensitivity reaction in people with pre-existing immunity toC. burnetii, limiting wider use. Consequently, a less reactogenic vaccine is needed. Here, we investigated contributions of theC. burnetiiDot/Icm type IVB secretion system (T4BSS) and lipopolysaccharide (LPS) in protection and reactogenicity of fixed WCVs. A 32.5 kb region containing 23dot/icmgenes was deleted in the virulent Nine Mile phase I (NMI) strain and the resulting mutant was evaluated in guinea pig models ofC. burnetiiinfection, vaccination-challenge, and post-vaccination hypersensitivity. The NMI ∆dot/icmstrain was avirulent, protective as a WCV against a robustC. burnetiichallenge, and displayed potentially altered reactogenicity compared to NMI. Nine Mile phase II (NMII) strains ofC. burnetiithat produce rough LPS, were similarly tested. NMI was significantly more protective than NMII as a WCV; however, both vaccines exhibited similar reactogenicity. Collectively, our results indicate that, like phase I LPS, the T4BSS is required for full virulence byC. burnetii. Conversely, unlike phase I LPS, the T4BSS is not required for vaccine-induced protection. LPS length does not appear to contribute to reactogenicity while the T4BSS may contribute to this response. NMI ∆dot/icmrepresents an avirulent phase I strain with full vaccine efficacy, illustrating the potential of genetically modifiedC. burnetiias improved WCVs.