Biological and immunological properties of Coxiella burnetii vaccines in C57BL/10ScN endotoxin-nonresponder mice

Vaccine development: obligate intracellular bacteria new tools, old pathogens: the current state of vaccines against obligate intracellular bacteria

Obligate intracellular bacteria have remained those for which effective vaccines are unavailable, mostly because protection does not solely rely on an antibody response. Effective antibody-based vaccines, however, have been developed against extracellular bacteria pathogens or toxins. Additionally, obligate intracellular bacteria have evolved many mechanisms to subvert the immune response, making vaccine development complex. Much of what we know about protective immunity for these pathogens has been determined using infection-resolved cases and animal models that mimic disease. These studies have laid the groundwork for antigen discovery, which, combined with recent advances in vaccinology, should allow for the development of safe and efficacious vaccines. Successful vaccines against obligate intracellular bacteria should elicit potent T cell memory responses, in addition to humoral responses. Furthermore, they ought to be designed to specifically induce strong cytotoxic CD8+ T cell responses for protective immunity. This review will describe what we know about the potentially protective immune responses to this group of bacteria. Additionally, we will argue that the novel delivery platforms used during the Sars-CoV-2 pandemic should be excellent candidates to produce protective immunity once antigens are discovered. We will then look more specifically into the vaccine development for Rickettsiaceae, Coxiella burnetti, and Anaplasmataceae from infancy until today. We have not included Chlamydia trachomatis in this review because of the many vaccine related reviews that have been written in recent years.

Q Fever Vaccine Development: Current Strategies and Future Considerations

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.

Neutrophils play an important role in protective immunity against Coxiella burnetii infection

Coxiella burnetii is an obligate intracellular Gram-negative bacterium that causes the zoonotic disease Q fever. Although Q fever is mainly transmitted by aerosol infection, study of the immune responses in the lung following pulmonary C. burnetii infection is lacking. Neutrophils are considered the first immune cell to migrate into the lung and play an important role in host defense against aerosol infection with microbial pathogens. However, the role of neutrophils in the host defense against C. burnetii infection remains unclear. To determine the role of neutrophils in protective immunity against C. burnetii infection, the RB6-8C5 antibody was used to deplete neutrophils in mice before intranasal infection with C. burnetii. The results indicated that neutrophil-depleted mice developed more severe disease than their wild-type counterparts, suggesting that neutrophils play an important role in host defense against C. burnetii pulmonary infection. We also found that neither CXC chemokine receptor 2 (CXCR2) nor interleukin-17 (IL-17) receptor (IL-17R) deficiency changed the severity of disease following intranasal C. burnetii challenge, suggesting that keratinocyte-derived chemokine and IL-17 may not play essential roles in the response to C. burnetii infection. However, significantly higher C. burnetii genome copy numbers were detected in the lungs of IL-1R(-/-) mice at 14 days postinfection. This indicates that IL-1 may be important for the clearance of C. burnetii from the lungs following intranasal infection. Our results also suggest that neutrophils are involved in protecting vaccinated mice from C. burnetii challenge-induced disease. This is the first study to demonstrate an important role for neutrophils in protective immunity against C. burnetii infection.

Chloroform-Methanol Residue of Coxiella burnetii Markedly Potentiated the Specific Immunoprotection Elicited by a Recombinant Protein Fragment rOmpB-4 Derived from Outer Membrane Protein B of Rickettsia rickettsii in C3H/HeN Mice

The obligate intracellular bacteria, Rickettsia rickettsii and Coxiella burnetii, are the potential agents of bio-warfare/bio-terrorism. Here C3H/HeN mice were immunized with a recombinant protein fragment rOmp-4 derived from outer membrane protein B, a major protective antigen of R. rickettsii, combined with chloroform-methanol residue (CMR) extracted from phase I C. burnetii organisms, a safer Q fever vaccine. These immunized mice had significantly higher levels of IgG1 and IgG2a to rOmpB-4 and interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α), two crucial cytokines in resisting intracellular bacterial infection, as well as significantly lower rickettsial loads and slighter pathological lesions in organs after challenge with R. rickettsii, compared with mice immunized with rOmpB-4 or CMR alone. Additionally, after challenge with C. burnetii, the coxiella loads in the organs of these mice were significantly lower than those of mice immunized with rOmpB-4 alone. Our results prove that CMR could markedly potentiate enhance the rOmpB-4-specific immunoprotection by promoting specific and non-specific immunoresponses and the immunization with the protective antigen of R. rickettsii combined with CMR of C. burnetii could confer effective protection against infection of R. rickettsii or C. burnetii.

Q Fever and Experimental Sheep

In August 1983 a Symposium was held in Vancouver to discuss Q fever as a hazard to humans in contact with infected sheep. On the basis of new preliminary information presented and discussion at the Symposium, an attempt has been made in this document to supplement published guidelines for the conduct of sheep research.

Vaccination against Q fever for biodefense and public health indications

Coxiella burnetii is the etiological agent of Q fever, a disease that is often spread to humans via inhalational exposure to the bacteria from contaminated agricultural sources. Outbreaks have been observed all over the world with larger foci generating interest in vaccination programs, most notably in Australia and the Netherlands. Importantly, exposure rates among military personnel deployed to the Middle East can be relatively high as measured by seroconversion to C. burnetii-specific antibodies. Q fever has been of interest to the biodefense community over the years due to its low infectious dose and environmental stability. Recent advances in cell-free growth and genetics of C. burnetii also make this organism easier to culture and manipulate. While there is a vaccine that is licensed for use in Australia, the combination of biodefense- and public health-related issues associated with Q fever warrant the development of a safer and more effective vaccine against this disease.

Characterization of a lipopolysaccharide-targeted monoclonal antibody and its variable fragments as candidates for prophylaxis against the obligate intracellular bacterial pathogen Coxiella burnetii

Our previous study demonstrated that treatment of Coxiella burnetii with the phase I lipopolysaccharide (PI-LPS)-targeted monoclonal antibody (MAb) 1E4 significantly inhibited C. burnetii infection in mice, suggesting that 1E4 is a protective MAb. To determine whether passive transfer of antibodies (Abs) can provide protection against C. burnetii natural infection, we examined if passive transfer of 1E4 would protect SCID mice against C. burnetii aerosol infection. The results indicated that 1E4 conferred significant protection against aerosolized C. burnetii, suggesting that 1E4 may be useful for preventing C. burnetii natural infection. To further understand the mechanisms of 1E4-mediated protection and to test the possibility of using humanized 1E4 to prevent C. burnetii infection, we examined whether the Fab fragment of 1E4 (Fab1E4), a recombinant murine single-chain variable fragment (muscFv1E4), and a humanized single-chain variable fragment (huscFv1E4) retained the ability of 1E4 to inhibit C. burnetii infection. The results indicated that Fab1E4, muscFv1E4, and huscFv1E4 were able to inhibit C. burnetii infection in mice but that their ability to inhibit C. burnetii infection was lower than that of 1E4. In addition, treatment of C. burnetii with Fab1E4, muscFv1E4, or huscFv1E4 can block C. burnetii infection of macrophages. Interestingly, treatment of C. burnetii with huscFv1E4 can significantly reduce C. burnetii infectivity in human macrophages. This report provides the first evidence to demonstrate that the humanized variable fragments of an LPS-specific MAb can neutralize C. burnetii infection and appears to be a promising step toward the potential use of a humanized MAb as emergency prophylaxis against C. burnetii exposure.

Formalin-inactivated Coxiella burnetii phase I vaccine-induced protection depends on B cells to produce protective IgM and IgG

To further understand the mechanisms of formalin-inactivated Coxiella burnetii phase I (PI) vaccine (PIV)-induced protection, we examined if B cell, T cell, CD4(+) T cell, or CD8(+) T cell deficiency in mice significantly affects the ability of PIV to confer protection against a C. burnetii infection. Interestingly, compared to wild-type (WT) mice, PIV conferred comparable levels of protection in CD4(+) T cell- or CD8(+) T cell-deficient mice and partial protection in T cell-deficient mice but did not provide measurable protection in B cell-deficient mice. These results suggest that PIV-induced protection depends on B cells. In addition, anti-PI-specific IgM was the major detectable antibody (Ab) in immune sera from PIV-vaccinated CD4(+) T cell-deficient mice, and passive transfer of immune sera from PIV-vaccinated CD4(+) T cell-deficient mice conferred significant protection. These results suggest that T cell-independent anti-PI-specific IgM may contribute to PIV-induced protection. Our results also suggested that PIV-induced protection may not depend on complement activation and Fc receptor-mediated effector functions. Furthermore, our results demonstrated that both IgM and IgG from PIV-vaccinated WT mouse sera were able to inhibit C. burnetii infection in vivo, but only IgM from PIV-vaccinated CD4(+) T cell-deficient mouse sera inhibited C. burnetii infection. Collectively, these findings suggest that PIV-induced protection depends on B cells to produce protective IgM and IgG and that T cell-independent anti-PI-specific IgM may play a critical role in PIV-induced protection against C. burnetii infection.

Monitoring the perturbation of soil and groundwater microbial communities due to pig production activities

This study aimed to determine if biotic contaminants originating from pig production farms are disseminated into soil and groundwater microbial communities. A spatial and temporal sampling of soil and groundwater in proximity to pig production farms was conducted, and quantitative PCR (Q-PCR) was utilized to determine the abundances of tetracycline resistance genes (i.e., tetQ and tetZ) and integrase genes (i.e., intI1 and intI2). We observed that the abundances of tetZ, tetQ, intI1, and intI2 in the soils increased at least 6-fold after manure application, and their abundances remained elevated above the background for up to 16 months. Q-PCR further determined total abundances of up to 5.88 × 10(9) copies/ng DNA for tetZ, tetQ, intI1, and intI2 in some of the groundwater wells that were situated next to the manure lagoon and in the facility well used to supply water for one of the farms. We further utilized 16S rRNA-based pyrosequencing to assess the microbial communities, and our comparative analyses suggest that most of the soil samples collected before and after manure application did not change significantly, sharing a high Bray-Curtis similarity of 78.5%. In contrast, an increase in Bacteroidetes and sulfur-oxidizing bacterial populations was observed in the groundwaters collected from lagoon-associated groundwater wells. Genera associated with opportunistic human and animal pathogens, such as Acinetobacter, Arcobacter, Yersinia, and Coxiella, were detected in some of the manure-treated soils and affected groundwater wells. Feces-associated bacteria such as Streptococcus, Erysipelothrix, and Bacteroides were detected in the manure, soil, and groundwater ecosystems, suggesting a perturbation of the soil and groundwater environments by invader species from pig production activities.

Antigenic analysis for vaccines and diagnostics

Coxiella burnetii infection is frequently unrecognized or misdiagnosed, as symptoms generally mimic an influenza-like illness. However, the disease (Q fever) may result in chronic infection, usually manifesting as potentially fatal endocarditis. The development of a chronic fatigue-like sequela may also occur. Infected ruminants are the major reservoir for infection in humans, primarily through exposure to birth products or aerosols that transmit the bacterium over wide regions. A vaccine against C. burnetii infection has been in use in Australia for abattoir and agricultural workers for many years. The possibility of adverse reactions in those with previous exposure to the agent has prevented its use elsewhere. Subunit vaccines, utilizing chemical extraction of components thought to cause adverse reactions, are in development, but none are yet licensed. Others have sought to combine immunogenic peptides with or without selected lipopolysaccharide components to produce a vaccine without the possibility of adverse reactions. Selected immunogenic proteins have been shown to induce both humoral and cellular immune responses. Although current diagnosis of infection relies on serological testing, the presentation of specific antibody occurs 7-15 days following the onset of symptoms, delaying treatment that may result in prolonged morbidity. PCR detection of DNA to specific C. burnetii antigens in the blood is possible early in infection, but PCR may become negative when PII IgG antibodies appear. PCR is useful for early diagnosis when Q fever is suspected, as in large epidemics, and shortens the delay in the identification of Q fever endocarditis. Others have combined PCR with ELISA or other methods to increase the ability to detect infection at any stage. The search for new diagnostic reagents and vaccines has utilized new methods for discovery of immunoreactive proteins. DNA analysis of the heterogeneity of C. burnetii isolates has led to a greater understanding of the diversity of isolates and a means to determine whether there is a correlation between strain and disease severity. 2-D SDS PAGE of immunogenic proteins reactive with human or animal infection sera and mass spectrometric analysis of specific secreted or outer membrane proteins have identified candidate antigens. Microarrays have allowed the analysis of peptide libraries of open reading frames to evaluate the immunogenicity of complete genomes.

Animal models of Q fever (Coxiella burnetii)

Q fever, caused by the pathogen Coxiella burnetii, is an acute disease that can progress to become a serious chronic illness. The organism leads an obligate, intracellular lifecycle, during which it multiplies in the phagolytic compartments of the phagocytic cells of the immune system of its hosts. This characteristic makes study of the organism particularly difficult and is perhaps one of the reasons why, more than 70 y after its discovery, much remains unknown about the organism and its pathogenesis. A variety of animal species have been used to study both the acute and chronic forms of the disease. Although none of the models perfectly mimics the disease process in humans, each opens a window onto an important aspect of the pathology of the disease. We have learned that immunosuppression, overexpression of IL10, or physical damage to the heart muscle in mice and guinea pigs can induce disease that is similar to the chronic disease seen in humans, suggesting that this aspect of disease may eventually be fully understood. Models using species from mice to nonhuman primates have been used to evaluate and characterize vaccines to protect against the disease and may ultimately yield safer, less expensive vaccines.

Long-Term immune responses to Coxiella burnetii after vaccination

Q fever is a zoonotic disease caused by infection with the bacterium Coxiella burnetii. Infection with C. burnetii results in humoral and cellular immune responses, both of which are thought to contribute to protection against subsequent infection. Whole-cell formalin-inactivated vaccines have also been shown to induce both humoral and cellular immunity and provide protection. Whether measurement of cellular or humoral immunity is a better indicator of immune protection is not known, and the duration of immunity induced by natural infection or vaccination is also poorly understood. To better understand the measurement and duration of C. burnetii immunity, 16 people vaccinated against Q fever (0.2 to 10.3 years before analysis) and 29 controls with a low risk of Q fever exposure were tested for immune responses to C. burnetii by an indirect fluorescent-antibody test (IFA) to measure circulating antibody and by a gamma interferon release assay (IGRA) to measure cellular immunity. Among vaccinated subjects, the IFA detected antibodies in 13/16, and the IGRA also detected positive responses in 13/16. All of the vaccinated subjects had a positive response in at least one of the assays, whereas 8/29 control subjects were positive in at least one assay. There was not a correlation between time since vaccination and responses in these assays. These results show that IFA and IGRA perform similarly in detection of C. burnetii immune responses and that Q fever vaccination establishes long-lived immune responses to C. burnetii.

Development of a lipopolysaccharide-targeted peptide mimic vaccine against Q fever

Coxiella burnetii is a Gram-negative bacterium that causes acute and chronic Q fever in humans. Creation of a safe and effective new generation vaccine to prevent Q fever remains an important public health goal. Previous studies suggested that Ab-mediated immunity to C. burnetii phase I LPS (PI-LPS) is protective. To identify the potential peptides that can mimic the protective epitopes on PI-LPS, a PI-LPS-specific mAb 1E4 was generated, characterized, and used to screen a phage display library. Interestingly, our results indicate that 1E4 was able to inhibit C. burnetii infection in vivo, suggesting that 1E4 is a protective mAb. After three rounds of biopanning by 1E4 from the phage display library, a mimetic peptide, m1E41920, was identified, chemically synthesized, and conjugated to keyhole limpet hemocyanin (KLH) for examining its immunogenicity. The results indicate that the synthetic peptide m1E41920 was able to inhibit the binding of 1E4 to PI Ag, suggesting m1E41920 shares the same binding site of 1E4 with the epitopes of PI Ag. In addition, m1E41920-KLH elicited a specific IgG response to PI Ag, and immune sera from m1E41920-KLH-immunized mice was able to inhibit C. burnetii infection in vivo, suggesting that m1E41920 may specifically mimic the protective epitope of PI-LPS. Furthermore, m1E41920-KLH was able to confer significant protection against C. burnetii challenge. Thus, m1E41920-KLH is a protective Ag and may be useful for developing a safe and effective vaccine against Q fever. This study demonstrates the feasibility of developing a peptide mimic vaccine against Q fever.

Q Fever: current state of knowledge and perspectives of research of a neglected zoonosis

Q fever is an ubiquitous zoonosis caused by an resistant intracellular bacterium, Coxiella burnetii. In certain areas, Q fever can be a severe public health problem, and awareness of the disease must be promoted worldwide. Nevertheless, knowledge of Coxiella burnetii remains limited to this day. Its resistant (intracellular and environmental) and infectious properties have been poorly investigated. Further understanding of the interactions between the infected host and the bacteria is necessary. Domestic ruminants are considered as the main reservoir of bacteria. Infected animals shed highly infectious organisms in milk, feces, urine, vaginal mucus, and, very importantly, birth products. Inhalation is the main route of infection. Frequently asymptomatic in humans and animals, Q fever can cause acute or chronic infections. Financial consequences of infection can be dramatic at herd level. Vaccination with inactive whole-cell bacteria has been performed and proved effective in humans and animals. However, inactive whole-cell vaccines present several defects. Recombinant vaccines have been developed in experimental conditions and have great potential for the future. Q fever is a challenging disease for scientists as significant further investigations are necessary. Great research opportunities are available to reach a better understanding and thus a better prevention and control of the infection.

The role of wild rodents in spread and transmission of Coxiella burnetii needs further elucidation

Rodents are known to cause massive food losses, but are also implicated as reservoirs for a wide variety of zoonotic pathogens. This review discusses the contribution of rodents in the spread and transmission of Coxiella burnetii, the causative agent of Q-fever. We found that rodents have been implicated as reservoirs for Q-fever, but their role in pathogen maintenance, geographic spread and transmission still remains to be clarified. As there are indications for a role of rodents in Q-fever epidemiology, including during the 2007–10 outbreak in the Netherlands, the overall lack of knowledge on the role of rodents warrants studies into their contribution in transmission of C. burnetii from the sylvatic cycle to the domestic cycle, in within-herd transmission, in transmission to surrounding farms and in direct transmission to humans. Although the basic sylvatic and domestic cycles of C. burnetii infection can operate independently, they will overlap in many instances as many areas in the world are occupied by both domestic and wild animals. This area of Q-fever ecology is of interest and research should focus on this aspect of Q-fever epidemiology and, in particular, on the role of rodents therein. More studies are needed that elicit the exact role of rodents in epidemiology of C. burnetii to further optimise disease control.

Dose-response model of Coxiella burnetii (Q fever)

Q fever is a zoonotic disease caused by the intracellular gram-negative bacterium Coxiella burnetii (C. burnetii), which only multiplies within the phagolysosomal vacuoles. Q fever may manifest as acute or chronic disease. The acute form is generally not fatal and manifestes as self-controlled febrile illness. Chronic Q fever is usually characterized by endocarditis. Many animal models, including humans, have been studied for Q fever infection through various exposure routes. The studies considered different endpoints including death for animal models and clinical signs for human infection. In this article, animal experimental data available in the open literature were fit to suitable dose-response models using maximum likelihood estimation. Research results for tests of severe combined immunodeficient mice inoculated intraperitoneally (i.p.) with C. burnetii were best estimated with the Beta-Poisson dose-response model. Similar inoculation (i.p.) trial outcomes conducted on C57BL/6J mice were best fit by an exponential model, whereas those tests run on C57BL/10ScN mice were optimally represented by a Beta-Poisson dose-response model.

Immunoreactive Coxiella burnetii Nine Mile proteins separated by 2D electrophoresis and identified by tandem mass spectrometry

Coxiella burnetii is a Gram-negative obligate intracellular pathogen and the causative agent of Q fever in humans. Q fever causes acute flu-like symptoms and may develop into a chronic disease leading to endocarditis. Its potential as a bioweapon has led to its classification as a category B select agent. An effective inactivated whole-cell vaccine (WCV) currently exists but causes severe granulomatous/necrotizing reactions in individuals with prior exposure, and is not licensed for use in most countries. Current efforts to reduce or eliminate the deleterious reactions associated with WCVs have focused on identifying potential subunit vaccine candidates. Both humoral and T cell-mediated responses are required for protection in animal models. In this study, nine novel immunogenic C. burnetii proteins were identified in extracted whole-cell lysates using 2D electrophoresis, immunoblotting with immune guinea pig sera, and tandem MS. The immunogenic C. burnetii proteins elicited antigen-specific IgG in guinea pigs vaccinated with whole-cell killed Nine Mile phase I vaccine, suggesting a T cell-dependent response. Eleven additional proteins previously shown to react with immune human sera were also antigenic in guinea pigs, showing the relevance of the guinea pig immunization model for antigen discovery. The antigens described here warrant further investigation to validate their potential use as subunit vaccine candidates.

Low-dose priming before vaccination with the phase I chloroform-methanol residue vaccine against Q fever enhances humoral and cellular immune responses to Coxiella burnetii

Although the phase I Coxiella burnetii cellular vaccine is completely efficacious in humans, adverse local and systemic reactions may develop if immune individuals are inadvertently vaccinated. The phase I chloroform-methanol residue (CMRI) vaccine was developed as a potentially safer alternative. Human volunteers with no evidence of previous exposure to C. burnetii received a subcutaneous vaccination with the CMRI vaccine in phase I studies under protocol IND 3516 to evaluate the safety and immunogenicity of the vaccine. This clinical trial tested escalating doses of the CMRI vaccine, ranging from 0.3 to 60 microg, followed by a booster dose of 30 microg, in a placebo-controlled study. Although priming doses of the CMRI vaccine did not induce a specific antibody detectable by enzyme-linked immunosorbent assay, booster vaccination stimulated the production of significant levels of anti-C. burnetii antibody. Peripheral blood cells (PBCs) of vaccinees responded to C. burnetii cellular antigen in vitro in a vaccine dose-dependent manner. After the booster dose, PBCs were activated by recall antigen in vitro, regardless of the priming dose. These findings suggest that vaccination with the CMRI vaccine can effectively prime the immune system to mount significant anamnestic responses after infection.

Mechanisms of vaccine-induced protective immunity against Coxiella burnetii infection in BALB/c mice

To elucidate the mechanisms of vaccine-induced protective immunity against Coxiella burnetii infection, we compared the protective efficacy and immunogenicity between formalin-inactivated phase I vaccine (PI-V) and phase II vaccine (PII-V) in BALB/c mice. PI-V generated significant protection while PII-V did not confer measurable protection. Analysis of cytokine and subclass Ab responses indicated that both PI-V and PII-V were able to induce a Th1-dominant immune response but did not identify the component of host response that distinguished their ability to induce protective immunity. Interestingly, immunoblot analysis identified a difference between PI-V and PII-V vaccinates in antigenic recognition by specific Ab isotypes. The observation that PI-LPS elicited significant protection but PII-LPS did not confer measurable protection suggests PI-LPS may play a key role in PI-V-induced protection. Adoptive transfer of either immune sera or splenocytes mediated significant protection in naive BALB/c mice, supporting the notion that both humoral and cellular immunity are important for development of protective immunity. However, the evidence that immune sera and B cells were unable to control infection while T cells conferred significant protection in SCID mice supports the hypothesis that T cell-mediated immunity is critical for host defense against C. burnetii infection. This report presents novel evidence to highlight the importance of PI-LPS and Abs in protective immunity and has important implications for the design of new generation vaccines against Q fever.

Coxiella burnetii: host and bacterial responses to infection

Designation as a Category B biothreat agent has propelled Coxiella burnetii from a relatively obscure, underappreciated, "niche" microorganism on the periphery of bacteriology, to one of possibly great consequence if actually used in acts of bioterrorism. Advances in the study of this microorganism proceeded slowly, primarily because of the difficulty in studying this obligate intracellular pathogen that must be manipulated under biosafety level-3 conditions. The dogged determination of past and current C. burnetii researchers and the application of modern immunological and molecular techniques have more clearly defined the host and bacterial response to infection. This review is intended to provide a basic introduction to C. burnetii and Q fever, while emphasizing immunomodulatory properties, both positive and negative, of Q fever vaccines and C. burnetii infections.

Effect of vaccination with phase I and phase II Coxiella burnetii vaccines in pregnant goats

Livestock is considered to be the major "source" of human Q fever. The efficacy of two currently available vaccines (Coxevac, phase I, CEVA Santé Animale and Chlamyvax FQ, phase II, MERIAL) against Coxiella excretion was investigated in terms of risks to human health. Two months before mating, 17 goats were vaccinated subcutaneously against Coxiella burnetii with an inactivated phase I vaccine and 16 goats were vaccinated with an inactivated phase II Coxiella mixed with Chlamydophila abortus vaccine. Fourteen goats were left unvaccinated. At 84 days of gestation, the goats were subcutaneously challenged with 10(4) bacteria of C. burnetii strain CbC1. Phase I vaccine was effective and dramatically reduced both abortion and excretion of bacteria in the milk, vaginal mucus and feces. In contrast, the phase II vaccine did not affect the course of the disease or excretion.

Identification and cloning of immunodominant antigens of Coxiella burnetii

A sublethal-challenge model was established in BALB/c mice by using protection from the development of severe splenomegaly as an indicator of vaccinogenic activity for evaluation of the protective efficacies of vaccine candidates. To determine the immunodominant antigens as defined by reaction to an infection-derived antibody, mouse sera from different stages of experimental infection with various doses of Coxiella burnetii were tested by immunoblotting. Proteins with molecular masses of 14, 16, 21, 28, 32, 45 to 50, 57, and 60 kDa were recognized as immunodominant antigens. Antibody responses in whole-cell antigen (WCA)-vaccinated mice were compared with those in unvaccinated mice by immunoblotting using two-dimensional gel-separated C. burnetii antigens. The results indicated that there were significantly different antibody responses during different stages of vaccination and challenge, suggesting that several specific immunogenic antigens may play critical roles in the protection of mice against challenge. To clone these immunogenic antigens, a genomic DNA library of Nine Mile phase I was screened with convalescent-phase antisera from mice. Eighteen novel immunoreactive proteins with molecular masses ranging from approximately 14 to 67 kDa were cloned and identified. Interestingly, several recombinant proteins reacted with sera from both early-stage infected and WCA-vaccinated prechallenged mice. These results suggest that these proteins may play critical roles in the development of protective immunity and that they are logical candidates for vaccine and serodiagnostic reagents.

Identification and cloning potentially protective antigens of Coxiella burnetii using sera from mice experimentally infected with Nine Mile phase I

Coxiella burnetii is an obligate intracellular bacterium that causes acute Q fever and occasional chronic infections in humans. To determine the immunodominant antigens during infection with C. burnetii, sera from mice experimentally infected with Nine Mile phase I were tested by immunoblotting. The mouse sera recognized antigens with a variety of molecular weights, including proteins of 14, 22, 28, 34, and 60 kDa as immunodominant antigens. In order to clone potential protective antigens, a genomic DNA library of Nine Mile phase I was constructed in the expression vector Lambda ZAP Express and screened with sera from mice that recovered from C. burnetii infection. A total of 102 immunoreactive clones with various signal intensities were identified from about 8,000 plaques. These clones were purified and expressed in the excised plasmid pBK-CMV. The proteins expressed by these recombinant plasmids were analyzed by SDS-PAGE and immunoblotting. Fifty-four clones expressed immunoreactive proteins of molecular masses ranging from approximately 14 to 60 kDa. Sequence analysis and BLAST search of the recently completed genome sequence identified a variety of novel immunoreactive proteins. These proteins are logical vaccine candidates for testing protective activity against C. burnetii challenge. We established a sublethal challenge model in BALB/c mice with protection from the development of severe splenomegaly as an indicator of vaccinogenic activity. Further characterization of these proteins will provide essential information for developing novel, specific diagnostic reagents and potential subunit vaccine candidates against C. burnetii infection.

Comparative efficacy and immunogenicity of Q fever chloroform:methanol residue (CMR) and phase I cellular (Q-Vax) vaccines in cynomolgus monkeys challenged by aerosol

Preliminary evidence gathered in rodents and livestock suggested that a phase I chloroform:methanol residue (CMR) extracted vaccine was safe and efficacious in protecting these animals from challenge with the obligate phagolysosomal pathogen (Coxiella burnetii). Prior to the initiation of phase II studies in human volunteers, we compared, in non-human primates (Macaca fascicularis), the efficacy of CMR vaccine with Q-Vax, a licensed cellular Australian Q fever vaccine that has been demonstrated to provide complete protection in human volunteers. Vaccine efficacy was assessed by evaluating thoracic radiographs and the presence of fever and bacteremia in monkeys challenged by aerosol with Coxiella burnetii. Changes in blood chemistries, hematology, behavior and pulmonary function were also examined. CMR, whether administered in single 30 or 100 microg doses or two 30 microg subcutaneous doses, gave equivalent protection in vaccine recipients as a single 30 microg dose of Q-Vax. In addition, vaccination resulted in significant, although temporary, increases in specific antibody titers against C. burnetii phases I and II antigens. The C. burnetii CMR vaccine may be an efficacious alternative to cellular Q fever vaccines in humans.

Q fever

Q fever is a zoonosis with a worldwide distribution with the exception of New Zealand. The disease is caused by Coxiella burnetii, a strictly intracellular, gram-negative bacterium. Many species of mammals, birds, and ticks are reservoirs of C. burnetii in nature. C. burnetii infection is most often latent in animals, with persistent shedding of bacteria into the environment. However, in females intermittent high-level shedding occurs at the time of parturition, with millions of bacteria being released per gram of placenta. Humans are usually infected by contaminated aerosols from domestic animals, particularly after contact with parturient females and their birth products. Although often asymptomatic, Q fever may manifest in humans as an acute disease (mainly as a self-limited febrile illness, pneumonia, or hepatitis) or as a chronic disease (mainly endocarditis), especially in patients with previous valvulopathy and to a lesser extent in immunocompromised hosts and in pregnant women. Specific diagnosis of Q fever remains based upon serology. Immunoglobulin M (IgM) and IgG antiphase II antibodies are detected 2 to 3 weeks after infection with C. burnetii, whereas the presence of IgG antiphase I C. burnetii antibodies at titers of >/=1:800 by microimmunofluorescence is indicative of chronic Q fever. The tetracyclines are still considered the mainstay of antibiotic therapy of acute Q fever, whereas antibiotic combinations administered over prolonged periods are necessary to prevent relapses in Q fever endocarditis patients. Although the protective role of Q fever vaccination with whole-cell extracts has been established, the population which should be primarily vaccinated remains to be clearly identified. Vaccination should probably be considered in the population at high risk for Q fever endocarditis.

Comparative efficacy of a Coxiella burnetii chloroform:methanol residue (CMR) vaccine and a licensed cellular vaccine (Q-Vax) in rodents challenged by aerosol

Q fever is an acute and self-limited febrile illness caused by the obligate intracellular bacterium Coxiella burnetii. While phase I cellular Q fever vaccines are efficacious in humans, vaccination of immune individuals may result in sterile abscesses and granulomas. The chloroform:methanol residue vaccine (CMR) was developed as a safer alternative. The efficacy of a licensed phase I cellular vaccine (Q-Vax) was compared with that of CMR vaccine in A/J mice and Hartley guinea pigs challenged with virulent phase I C. burnetii by aerosol. Both vaccines were efficacious. The CMR vaccine dose required to protect 50% of mice (PD50) against lethal aerosol challenge (11 LD50) was one-third of the Q-Vax dose. However, the PD50 for CMR was four times the Q-Vax dose in guinea pigs challenged by aerosol (60 LD50). It was concluded that CMR is an efficacious alternative to cellular Q fever vaccines for the prevention of Q fever.

Characterization of the non-specific humoral and cellular antiviral immunity stimulated by the chloroform-methanol residue (CMR) fraction of Coxiella burnetii

Modulation of the immune response by the chloroform-methanol residue (CMR) of phase I Coxiella burnetii whole cell was studied in Rift Valley fever virus-infected, or in naive endotoxin-non-responder C3H/HeJ mice. A single dose of CMR completely protected the mice from viral infection. Treating virus-infected mice with antibodies directed against interferons alpha/beta (IFN-alpha beta) and gamma (IFN-gamma) eliminated the CMR-induced protection. CMR stimulated the production of high levels of IFN-alpha/beta and 2'-5'-oligoadenylate synthetase activities in sera of the CMR-treated mice. IFN-gamma was present in supernatants of cultured spleen cells of CMR-treated, virus-infected mice, but not in their serum. Priming mice with CMR optimized the release of INF-gamma, interleukin-1 alpha (IL-1 alpha) and IL-6 from splenocytes in vitro. When stimulated in vitro, IL-2 and granulocyte-macrophage stimulating factor (GM-CSF) did not require in vivo priming for release from cultured spleen cells. Fluorescence-assisted cytometry of CMR-treated mouse spleen cells showed there was a CMR-dependent increase in the percentage of T-cells and Ia-positive T-cells. There also was a biphasic increase in the ratio between Th (L3T4) and Ts (Lyt2) cells. Biological activities stimulated by CMR indicate that CMR is a potent immunostimulant, which may modulate specific and non-specific antiviral responses.

Efficacy of Coxiella burnetii and its chloroform-methanol residue (CMR) fraction against Rift Valley fever virus infection in mice

Strains of Coxiella burnetii phase I and II whole cells (WC-I and WC-II) or whole cell fractions were assessed for their potential to induce long-lasting protection in endotoxin-non-responder C3H/HeJ or CD-1 mice against Rift Valley fever (RVF) virus challenge. Among the whole cell fractions, only the chloroform-methanol residue (CMR), administered as a single dose (100 micrograms per mouse) 24 h before viral challenge, effectively protected 100% of the mice from RVF virus; the CMR of the Ohio strain of C. burnetii was not protective. Most of the RVF virus-infected mice treated with other C. burnetii cell fractions died, although their times to death varied. Lipopolysaccharide (LPS) associated with CMR preparations used in these studies, did not protect against RVF virus challenge. A single dose of 100 micrograms of CMR given 24 h before viral challenge completely eradicated 4-5 logs of RVF virus in the serum, liver, spleen, and central nervous system. Compared to several other immunomodulators, CMR was an equally effective antiviral agent. Efficacy of CMR of both Henzerling and Ohio strains disappeared or was marginal when treatment was initiated 2-3 days before RVF viral challenge, even when a second or a third dose of CMR was administered after challenge. A single dose of liposome-encapsulated CMR to RVF virus-infected mice extended the range of therapeutic efficacy of this biologically active component of C. burnetii to 4 days before infection.

Cell-mediated and humoral immune responses after vaccination of human volunteers with the live vaccine strain of Francisella tularensis

The specific humoral and cell-mediated immune responses of human volunteers vaccinated with the Francisella tularensis live vaccine strain (LVS) were evaluated. In the search for an optimal antigen to measure the immunogenicity of the vaccine in an enzyme-linked immunosorbent assay, we tested irradiation-killed LVS, an aqueous ether extract of the LVS (EEx), lipopolysaccharide (LPS) from LVS, and a virulent strain (SCHU4). Volunteers were immunized with LVS by scarification. Immunoglobulin G (IgG) responses to LVS and LPS gave the highest background titers when tested with sera from unimmunized volunteers, whereas IgA, IgG, and IgM background titers to EEx and SCHU4 were low. Vaccination caused a significant rise (P < 0.01) in IgA, IgG, and IgM titers to all antigens tested, except for the IgG response to LPS. Eighty percent of vaccinated volunteers developed a positive IgG response to EEx 14 days postvaccination, while 50% were positive to LVS. By day 14 after vaccination, 70% of immunized volunteers exhibited a positive response to EEx in an in vitro peripheral blood lymphocyte proliferation assay. EEx, a specific and sensitive antigen for evaluating immune responses of vaccinated volunteers, may be a superior antigen for the diagnosis of tularemia.

Safety and immunogenicity in human volunteers of a chloroform-methanol residue vaccine for Q fever

Current Q fever vaccines, consisting of Formalin-inactivated phase I whole Coxiella burnetii, are highly efficacious in preventing disease in high-risk settings but are associated with a risk of unacceptable local reactions in previously immune individuals and require cumbersome preliminary immunologic evaluation of potential vaccinees. A vaccine prepared from the residue of chloroform-methanol extraction of phase I Henzerling strain C. burnetii (CMR) has been shown to be less reactogenic but still immunogenic and protective in small animals and sheep. In a placebo-controlled trial, we immunized 35 healthy adults unscreened for markers of prior C. burnetii immunity with a single subcutaneous CMR dose of 30, 60, 120, or 240 micrograms. None of those receiving the 30- or 60-micrograms CMR dose and none of the placebo recipients experienced any adverse effects. Five of 15 120-micrograms dose CMR recipients complained of transient discomfort in the inoculated arm; erythema or induration of > or = 100 mm2 was noted in three and four, respectively, and two had malaise and low-grade fever (< 101 degrees F, orally). No 240-micrograms dose vaccinee reported limb discomfort, but 7 of 10 had erythema and/or induration of > or = 100 mm2 (P < 0.001 versus placebo). Two reported malaise, and one had low-grade fever. All adverse effects were self-limited. Serum immunoglobulin M responses were optimally detected with CMR antigen and occurred in 50, 60, 73, and 90% of recipients of the 30-, 60-, 120-, and 240-micrograms doses, respectively; results with phase I whole-cell antigen were similar. Serum immunoglobulin G responses were best detected with phase II antigen and were seen in 20, 20, and 40% of those receiving the 60-, 120-, and 240-micrograms doses, respectively. Peripheral blood T-cell proliferative responses to C. burnetii recall antigens were transient and of low magnitude but were seen with CMR antigen in 33% of 120-micrograms dose recipients and 40% of 240-micrograms dose recipients. Data from this study and those from comparative-efficacy trials in primates should provide the basis for field trials of the CMR vaccine.

Vaccines against coxiellosis and Q fever. Development of a chloroform:methanol residue subunit of phase I Coxiella burnetti for the immunization of animals

We have demonstrated the safety, immunogenicity, and efficacy of the WC and CMR vaccines in guinea pigs. Vaccination of guinea pigs with either WC or CMR protects animals against challenge with virulent C. burnetii. A total of 2 micrograms of either WC or CMR vaccine was a significant priming dose. A total of 20 micrograms gave complete protection against lethal challenge. Detection of antibodies to phase II cells by microaglutination, after vaccination with either WC or CMR and before lethal challenge, correlated with the ability of guinea pigs to mount a protective immune response. The PD50 values for WC and CMR vaccines, administered as a single dose, were 0.3 and 1.4 micrograms per animal, respectively. In contrast, the PD50 values for the WC and CMR vaccines, administered as two doses, were 0.83 and 0.72 micrograms per animal, respectively. Although the PD50 values for the two vaccines are similar, the CMR vaccine is preferred over the WC vaccine because it induces significantly fewer adverse reactions, and repeat injections can be given. Unvaccinated guinea pigs do not clear infectious microorganisms after challenge infection. Vaccination before challenge infection reduces the infectious load of C. burnetti in the blood and in various organs of the animals. When vaccinated animals were challenge infected and treated with rifampicin, the microorganisms were not eliminated from various organs. However, the combination of vaccination, challenge, and rifampicin treatment is effective in reducing the number of infectious microorganisms in some of these sites. We have demonstrated the safety and immunogenicity of the CMR vaccine in sheep and goats. Animals that were seropositive for one or more antigens developed significant levels of antibodies to alternate antigens, but no adverse reactions were observed at the site of s.c. injection of the CMR vaccine. This demonstrates that seropositive animals can be successfully immunized with this vaccine. These results also indicate that a long-term vaccination program using the CMR vaccine has the potential for producing animals with significant antibody titers to C. burnetii and perhaps lifelong immunity. The goal of a Q fever vaccination program is to produce immunized animals that are able to clear completely the infectious microorganisms. The appropriate vaccination schedule to render adult animals and their offspring "Q fever-free" should now be thoroughly investigated.

Antigenic differences between Coxiella burnetii cells revealed by postembedding immunoelectron microscopy and immunoblotting

The aim of this study was to investigate the antigenic structures of the morphologically distinct cells of the Coxiella burnetii developmental cycle. Postembedding immunoelectron microscopy with polyclonal antibodies produced in rabbits to (i) phase I cells, (ii) a chloroform-methanol residue fraction of cells, (iii) the cell walls (CW) of large and small cells and small dense cells (SDC), and (iv) the peptidoglycan-protein complexes of small cells and SDC labelled the continuum of morphologically distinct cells. But these antibodies did not distinguish between the antigenic structures of the various cells. Monoclonal antibodies to the phase I lipopolysaccharide labelled the CW of a majority of the smaller cells, but there was diminished reactivity to the larger cells. Although monoclonal antibodies to a 29.5-kDa outer membrane protein labelled the CW of the large mother cells, the large cells, and the small cells, a minority of the SDC with compact CW were not labelled. The endogenous spore within the mother cell was not labelled by the polyclonal or monoclonal antibodies to cellular components. A selected population of SDC was prepared by osmotic lysis of large cells, differential centrifugation, Renografin step-gradient fractionation, and breakage of the small cells in a French press at 20,000 lb/in2. The pressure-resistant SDC collected as fraction CL did not contain the 29.5-kDa protein, as evidenced by the lack of (i) Coomassie brilliant blue staining of protein in the 29.5-kDa region of sodium dodecyl sulfate-polyacrylamide gels and (ii) reactivity of the 29.5-kDa protein antigenic epitopes in immunoblotting with monoclonal antibodies to the protein. In contrast, CW of the pressure-sensitive small cells contained the 29.5-kDa protein. Therefore, the observed ultrastructural differences between large and small cells and SDC reflect differences in sensitivity to breakage by pressure treatment and in cell-associated antigens. Although the process of differentiation in C. burnetii remains an enigma, we have taken steps toward identifying cellular antigens as markers of differentiation. The pressure-resistant SDC in fraction CL that are devoid of the 29.5-kDa protein may be useful for answering questions about the physiological events required for triggering outgrowth and sequential regulation of the Coxiella developmental cycle.

Sequential release of antigens from chloroform-treated Staphylococcus epidermidis: application towards a possible vaccine

This study describes the properties of two potential Staphylococcus epidermidis vaccines prepared by chloroform treatment of bacteria and release of antigen from these chloroform-treated organisms. Both vaccines were antigenic on testing with homologous hyperimmune serum and induced immune reactivity in immunized rabbits. There was protective efficacy in mice against intraperitoneal challenge by Staph. epidermidis.

Injection of inactivated phase I Coxiella burnetii increases non-specific resistance to infection and stimulates lymphokine production in mice

The encounter of phase I C. burnetii with the host results in seemingly disparate consequences. On the one hand, in vitro lymphocyte responses to mitogens and homologous recall antigen are suppressed. On the other, host resistance to a variety of infectious agents and to a tumor is increased. An explanation for this augmented immune response surely involves the ability of C. burnetii to stimulate cytokines, such as interferon and TNF, which enhance host immune function.

Clinical aspects and prevention of Q fever in animals

The natural reservoir of Coxiella burnetii encompasses many free-living vertebrates but the major risk of human infection arises through contact with infected ruminant livestock and their contaminated products. The organism has a remarkable affinity for the ruminant placenta and mammary gland but the great majority of naturally-occurring infections are asymptomatic. However, the potential of C. burnetii to cause abortion has been demonstrated experimentally and observed in the field while more recent evidence has implied a contributory role in bovine infertility. Empirical vaccines incorporating inactivated whole cells of C. burnetii or derivatives have induced varying degrees of protection of cattle and sheep against both natural and experimental challenge but, in some cases, severe reactions have occurred at inoculation sites. Modifications in processes of antigen preparation seem to overcome this problem. Discrimination between antibodies resulting from natural infection and those induced by vaccination is possible using ELISAs with specificity for individual immunoglobulin isotypes.

Novel virulence properties of the Salmonella typhimurium virulence-associated plasmid: immune suppression and stimulation of splenomegaly

Mice infected subcutaneously with wild-type Salmonella typhimurium, SR11, developed a significant splenomegaly when compared with mice infected with an equal number of a plasmid-cured strain. Further, the bacterial load in the spleen at 14 days after infection, measured as colony-forming units per gram tissue, was significantly higher in mice infected with the parent strain than in mice infected with the plasmid-cured strain. These data confirm the previously reported plasmid-associated ability of Salmonella to multiply within the spleen. In addition, lymph node cells (LNC) from mice infected with the parent strain had a significantly reduced ability to proliferate in response to concanavalin A, a T-cell mitogen, and to heat-killed S. typhimurium cells when compared with LNC isolated from mice infected with the plasmid-cured strain. Finally, reintroduction of a functional Tn5-tagged 90-kb plasmid into a plasmid-free strain restored its capacity to cause a marked splenomegaly and to suppress lymph node cell proliferation in BALB/c mice. These data demonstrate that the 90-kb plasmid of highly virulent S. typhimurium strains mediates several novel pathogenic properties in infected mice: (1) enhancement of the ability of Salmonella to multiply within the spleen; (2) stimulation of a splenic inflammatory response as displayed by marked splenomegaly; and (3) a general suppression of lymphocyte responsiveness to both T-cell mitogens and specific Salmonella antigens.

A heat shock operon in Coxiella burnetti produces a major antigen homologous to a protein in both mycobacteria and Escherichia coli

A gene library from the DNA of Coxiella burnetii has been constructed in the cosmid vector pHC79. A particular clone, pJB196, reacted strongly with Coxiella-specific antibodies elicited in a number of different species of animals. This clone produced two abundant C. burnetii-specific polypeptides, a 14-kilodalton nonimmunoreactive protein and a 62-kilodalton immunoreactive protein. Sequencing identified two open reading frames, encoding polypeptides of 10.5 and 58.3 kilodaltons. The only transcriptional control element observed on the 5' side of the initiation codon resembled a heat shock promoter. This heat shock promoter was functionally regulated in Escherichia coli, since both proteins were produced by growth conditions at 37 degrees C and neither protein was detected at 23 degrees C. There were four sequences from the literature that were highly homologous (greater than 50%) to the 62-kilodalton protein from C. burnetii. Three were from Mycobacterium species and represent the immunodominant antigen of this genus. The other was from E. coli, detected as a gene that complements or suppresses a temperature-sensitive RNase activity. Since the recombinant protein was immunogenic, it may serve as an efficacious vaccine against C. burnetii and other pathogenic microorganisms that express the conserved antigen.

Immune modulation by Coxiella burnetii: characterization of a phase I immunosuppressive complex differentially expressed among strains

Coxiella burnetii, the etiological agent of Q fever, possesses immunomodulatory activity which positively and negatively regulates host immune responses. We wish to determine the Coxiella strain differences and the chemical nature of cellular components suppressing lymphocyte responsiveness. The bacterial components responsible for the immunomodulatory activity are associated with phase I cells. In its natural state, the phase I cell-associated, immunosuppressive complex (ISC) was resistant to chemical and enzymatic treatment. The ISC was inactivated and rendered accessible by chloroform-methanol (CM) (4:1) extraction of phase I cells which produced a CM residue (CMRI) and CM extract (CME). The suppressive components in either CMRI or CME did not induce ISC activity in the host when injected separately. Reconstitution of the CMRI with CME prior to injection produced the same pathological reactions characteristic of phase I cells. The CMRI suppressive component was sensitive to alkali, acid, periodate, lysozyme, and neuraminidase, but resistant to lipase and protease. An active component of CMRI was attached to the cell matrix by disulphide bonds. The amphipathic, lipophilic, CME suppressive component was ubiquitously distributed in procaryotes and eukaryotes because ISC activity of CMRI was regained after association with reagent-grade lipids and different CMEs. The ISC was expressed by phase I strains with smooth lipopolysaccharide (LPS) but not by phase II strains with rough LPS. Phase I heart valve strains carrying significant amounts of rough LPS did not express all of the biological properties of the ISC. The LPS molecule induced immune enhancement without immunosuppression. Thus, expression of the ISC showed strain variation and may be under genetic control. The complete details of the chemical composition and active components of the ISC should prove useful for biological-response-modification studies.

Q fever vaccines: present status and application in man

Of three Q fever vaccine candidates available at present, i.e., phase I corpuscular untreated, soluble, and phase I corpuscular chloroform-methanol treated vaccines, the first two were tested on hundreds of subjects exposed to Q fever. Based on their sufficient immunogenicity (which depends also on the tests employed) and low reactogenicity (providing that subjects with previous contact with Coxiella (C.) burnetii are excluded from vaccination) these two vaccines can be recommended for vaccination of humans at risk. Further studies are required, however, to answer definitively which vaccine type is the most suitable, and facing the problem of C. burnetii strain heterogeneity, to decide whether a monovalent vaccine will be sufficient or a polyvalent vaccine will be necessary.

Reduced immune responsiveness and lymphoid depletion in mice infected with Ehrlichia risticii

The histopathology of the thymus and spleen and the response of spleen cells to mitogenic stimuli were evaluated in Sprague-Dawley CF-1 mice infected with Ehrlichia risticii. Intraperitoneal injection of 10(4) or 10(6) E. risticii-infected U-937 cells into mice resulted in 100% morbidity and partial mortality. Thymic atrophy became significant between 1 and 2 weeks postinfection and remained for the duration of the study. The atrophy appeared associated with antecedent destruction and rarefaction of lymphocytes, resulting in the loss of corticomedullary demarcation. Splenomegaly was prominent; significantly increased weights were detected 7 days postinfection. Histopathologic examination revealed rarefaction of lymphocytes around central arteries, the presence of necrotic debris in histiocytes, and replacement of erythropoiesis by granulopoiesis in the red pulp. Marked and acute reduction of in vitro proliferative responses of spleen cells to concanavalin A (ConA) and phytohemagglutinin were observed in mice infected with 10(4) or 10(6) E. risticii-infected U-937 cells. Interleukin-2 activity in the supernatant of ConA-stimulated spleen cells was also severely reduced. Both changes were time- and dose-dependent and were not associated with decreased spleen cell viability. Neither morbidity nor mortality occurred in mice infected with 10(2) E. risticii-infected U-937 cells. Although there was temporal reduction in phytohemagglutinin-driven lymphocyte proliferation, reduction in neither ConA-driven lymphocyte proliferation nor interleukin-2 activity was observed with this dosage. All E. risticii-inoculated mice seroconverted between days 18 and 25, as detected by the indirect fluorescent-antibody procedure. The findings indicate for the first time the hypoimmune responsiveness and histopathologic changes in lymphoid organs associated with E. risticii infection.

Human T helper cells specific for antigens of typhus group rickettsiae enhance natural killer cell activity in vitro

The peripheral blood mononuclear cells (PBMC) from 5 individuals immune to typhus group rickettsiae and from 13 nonimmune individuals were stimulated in vitro for 7 days with typhus group rickettsial antigen (TGRA). At the end of day 7, lysis of the natural killer (NK)-susceptible target K562 by these PBMC was determined. As controls, PBMC from both groups of donors were cultured in vitro for 7 days without antigen or were freshly isolated, and lysis of the K562 target was determined. There was no significant difference between the level of NK activity in freshly isolated PBMC from immune and nonimmune donors. PBMC from immune donors which were stimulated with antigen for 7 days exhibited significantly greater NK activity than did the control population, which was cultured for 7 days without antigen. PBMC from immune donors which were stimulated with TGRA demonstrated significantly higher NK activity than the same PBMC stimulated with antigen derived from an antigenically unrelated rickettsia, Coxiella burnetii. There was no significant difference, however, in the level of NK activity of nonimmune antigen-stimulated PBMC compared with that of the same PBMC population cultured without antigen. Most of the antigen-stimulated NK activity was mediated by Leu-11-positive cells as determined by electronic cell sorting. The ability of TGRA to sustain the NK activity of PBMC from immune donors was abolished when the T4/Leu-3-positive population of lymphocytes was eliminated by positive or negative selection prior to antigen stimulation. The ability of TGRA to sustain the NK activity of PBMC from immune donors was also significantly decreased in the presence of antibodies against human interleukin-2. The results suggest that the activity of human NK cells can be sustained in vitro by antigen-specific T helper cells and that the effect of the T helper cell is mediated, at least in part, by interleukin-2.

Characterization of a phase I Coxiella burnetii chloroform-methanol residue vaccine that induces active immunity against Q fever in C57BL/10 ScN mice

The effect of phase I Coxiella burnetii chloroform-methanol residue vaccine (CMRV) on the response of murine splenic lymphocytes to mitogenic and antigenic stimuli was evaluated in C57BL/10 ScN endotoxinnonresponder mice with an in vitro lymphocyte proliferation assay. Intraperitoneal injection of phase I CMRV resulted in antibody production against phases I and II antigens. Lymphocytes were responsive in vitro to concanavalin A, phytohemagglutinin, pokeweed mitogen, and specific recall antigens. Antibodies against phases I and II antigens were not detected after intraperitoneal injection of chloroform-methanol extract (CME). Lymphocytes also were only slightly hyporesponsive to mitogens. Reconstitution of the CMRV with the CME of phase I whole cells restored the immunopathological reactions that were associated with the phase I whole cell vaccine (WCV). The CMRV was more mitogenic than the WCV for lymphocytes from mice injected with saline. Lymphocytes from phase I WCV-injected mice were negatively modulated with nontoxic concentrations of homologous WCV or CMRV. Lymphocytes from phase I CMRV-injected mice were only slightly hyporesponsive to mitogens and were significantly stimulated by antigens of either WCV or CMRV as recall antigens. Vaccination of mice with 100 micrograms of CMRV, CME, or WCV provided 80, 0, or 50% protection, respectively, against a lethal intraperitoneal challenge with viable phase I C. burnetii. The epitopes which induce immunological hyporesponsiveness, negative modulation, and the death of lymphocytes were fractionated into the CMRV and CME. The CMRV provides at least one of the determinants which induce immunosuppression, whereas CME contains specific or nonspecific components or both. Collectively, these results show that the CMRV may be a potential candidate to replace the WCV currently used for human vaccination.

Suppression of in vitro lymphocyte proliferation in C57BL/10 ScN mice vaccinated with phase I Coxiella burnetii

The effect of inactivated phase I and phase II Coxiella burnetii whole cell vaccine (WCV) on the response of murine spleen cells to mitogenic and antigenic stimuli was evaluated in C57BL/10 ScN endotoxin nonresponder mice with an in vitro lymphocyte proliferation assay. Intraperitoneal injection of phase I WCV into mice resulted in marked and persistent suppression of the proliferative response of spleen cells to concanavalin A, phytohemagglutinin, and pokeweed mitogen. This response was time and dose dependent and was not associated with decreased lymphocyte viability. By using a standard dose of 100 micrograms of phase I WCV, suppression of mitogenic responsiveness was first detected 3 days postinjection, attained maximum levels by day 14, and persisted for longer than 5 weeks. Suppression of mitogenic lymphocyte proliferation also was demonstrated after inoculation of animals with viable phase I organisms. The observed hyporesponsiveness of spleen cells from phase I WCV-injected animals was not either the result of a shift in the mitogenic dose optimum or due to a change in the day of in vitro peak response. Spleen cells from phase I WCV-injected mice were negatively regulated with homologous antigen. Investigation of the mechanism of action of phase I WCV, with a 51Cr-release assay, and trypan blue dye exclusion showed that phase I WCV was not directly cytolytic or cytotoxic to spleen cells from normal or vaccinated mice. Phase II WCV did not induce significant mitogenic hyporesponsiveness or negative modulation of spleen cells. These findings extend the observations of adverse host responses associated with the phase I WCV and underscore the need to develop a microbial fraction which possesses protective potency but which lacks the propensity to induce deleterious tissue reactions and immunosuppression.

Chemical and immunological characterization of lipopolysaccharides from phase I and phase II Coxiella burnetii

Lipopolysaccharides (LPSs) isolated from phase I and phase II Coxiella burnetii (LPS I and LPS II, respectively) were analyzed for chemical compositions, molecular heterogeneity by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and immunological properties. The yields of crude phenol-water extracts from phase I cells were roughly three to six times higher than those from phase II cells. Purification of LPSs by ultracentrifugation gave similar yields for both LPS I and LPS II. Purified LPS I and LPS II contained roughly 0.8 and 0.6% protein, respectively. The fatty acid constituents of the LPSs were different in composition and content, with branched-chain fatty acids representing about 15% of the total. beta-Hydroxymyristic acid was not detected in either LPS I or LPS II. A thiobarbituric acid-periodate-positive compound was evident in the LPSs; however, this component was not identified as 3-deoxy-D-mannooctulosonic acid by gas and paper chromatographies. LPS II contained D-mannose, D-glucose, D-glyceromannoheptose, glucosamine, ethanolamine, 3-deoxy-D-mannooctulosonic acid-like material, phosphate, and fatty acids. LPS I contained the unique disaccharide galactosaminuronyl glucosamine and nine unidentified components in addition to the components of LPS II. The hydrophobic, putative lipid A fraction of LPS I and LPS II contained the above constituents, but the hydrophilic fraction was devoid of ethanolamine. The LPS I disaccharide galactosaminuronyl glucosamine was found in both fractions of the acetic acid hydrolysates. Analysis of LPSs by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by silver staining indicated that LPS II was composed of only one band, whereas LPS I consisted of six or more bands with irregular spacing. Ouchterlony immunodiffusion tests demonstrated that LPS I reacted with phase I but not with phase II whole-cell hyperimmune antibody, and LPS II reacted neither with phase I nor phase II hyperimmune antibody. From these results, it was concluded that the chemical structures of LPSs from C. burnetii were different from those of the LPSs of gram-negative bacteria; however, the LPS structural variation in C. burnetii may be similar to the smooth-to-rough mutational variation of saccharide chain length in gram-negative bacteria.

Induction of hyperreactivity to endotoxin in mice by Coxiella burnetii

Intraperitoneal inoculation of mice with live or killed Coxiella burnetii phase I or phase II cells induced a marked hyperreactivity to the lethal effect of bacterial endotoxin and was accompanied by a marked hepatosplenomegaly. The degree and duration of hyperreactivity depended on the dose of C. burnetii administered and were higher with phase I than with phase II cells. Sensitization to the lethal effects of endotoxin and induction of splenomegaly by phase I C. burnetii cells also proceeded in the endotoxin-resistant C3H/HeJ strain of mice. Preincubation of C. burnetii cells with the corresponding immune serum significantly diminished the ability of phase I but not phase II cells to induce hyperreactivity to endotoxin.

Monoclonal antibodies distinguish phase variants of Coxiella burnetii

Monoclonal antibodies (MAbs) directed against phase I and II variants of Coxiella burnetii were produced by fusing myeloma SP2/O-AG 14 cells with spleen cells from mice immunized with the chloroform-methanol extraction residue of phase I whole cells. Two hybridoma clones which distinguished the phase variants by microimmunofluorescence assay were isolated and characterized. The MAbs showing specificity for phase I cells (MAbI-1, immunoglobulin G, subclass 3 kappa) reacted with the hot phenol-water extract of phase I C. burnetii in immunodiffusion and enzyme-linked immunosorbent assays. MAbI-1 reacted with high-molecular-weight components from phase I phenol-water extract and whole cell in an immunoblot assay. Specificity of MAbI-1 for a carbohydrate epitope in the phenol-water extract was demonstrated by periodic acid inactivation of binding by a competitive enzyme-linked immunosorbent assay. Phase I antigenic sites were apparently well represented on the surface of cells as demonstrated by complete fluorescence and microagglutination. The MAb showing specificity for phase II cells (MAbII-1, immunoglobulin G, subclass 2b kappa) reacted with whole cells in the microimmunofluorescence assay, microagglutination test, complement fixation test, and the enzyme-linked immunosorbent assay. MAbII-1 reacted specifically with a 29,500-dalton surface protein as demonstrated by immunoprecipitation of 125I-surface-labeled cells. Although MAbII-1 reacted with detergent-solubilized protein, it did not react with sodium-dodecyl sulfate-denatured protein by immunoblot assay. This protein was not exposed on the surface of phase I cells, but chloroform-methanol extraction of phase I cells exposed the phase II epitope.

Dermal granulomatous hypersensitivity in Q fever: comparative studies of the granulomatous potential of whole cells of Coxiella burnetii phase I and subfractions

Dermal granulomatous reactivity to Q fever antigens in guinea pigs has been described as a model for vaccine reactions seen in previously sensitized humans. This model has now been applied to study the ability of subfractions of Coxiella burnetii to produce granulomas. Q fever organisms in phase I, trichloroacetic acid-soluble and -insoluble fractions, and the extract and residue of chloroform-methanol extraction were tested for their relative ability to elicit and immunize for dermal granulomatous reactions and specific lymphocyte proliferative responses in guinea pigs. The results suggest that a determinant(s) causing granulomas can be removed by chloroform-methanol extraction of phase I whole cells. The chloroform-methanol residue elicited strong delayed-type hypersensitivity without subsequent granuloma formation. The chloroform-methanol residue appears to possess a determinant(s) for lymphocyte stimulation equivalent to that of whole phase I organisms.

Q fever and Coxiella burnetii: a model for host-parasite interactions

Images