Genome-wide epitope mapping across multiple host species reveals significant diversity in antibody responses to Coxiella burnetii vaccination and infection

Coxiella burnetii is an important zoonotic bacterial pathogen of global importance, causing the disease Q fever in a wide range of animal hosts. Ruminant livestock, in particular sheep and goats, are considered the main reservoir of human infection. Vaccination is a key control measure, and two commercial vaccines based on formalin-inactivated C. burnetii bacterins are currently available for use in livestock and humans. However, their deployment is limited due to significant reactogenicity in individuals previously sensitized to C. burnetii antigens. Furthermore, these vaccines interfere with available serodiagnostic tests which are also based on C. burnetii bacterin antigens. Defined subunit antigen vaccines offer significant advantages, as they can be engineered to reduce reactogenicity and co-designed with serodiagnostic tests to allow discrimination between vaccinated and infected individuals. This study aimed to investigate the diversity of antibody responses to C. burnetii vaccination and/or infection in cattle, goats, humans, and sheep through genome-wide linear epitope mapping to identify candidate vaccine and diagnostic antigens within the predicted bacterial proteome. Using high-density peptide microarrays, we analyzed the seroreactivity in 156 serum samples from vaccinated and infected individuals to peptides derived from 2,092 open-reading frames in the C. burnetii genome. We found significant diversity in the antibody responses within and between species and across different types of C. burnetii exposure. Through the implementation of three different vaccine candidate selection methods, we identified 493 candidate protein antigens for protein subunit vaccine design or serodiagnostic evaluation, of which 65 have been previously described. This is the first study to investigate multi-species seroreactivity against the entire C. burnetii proteome presented as overlapping linear peptides and provides the basis for the selection of antigen targets for next-generation Q fever vaccines and diagnostic tests.

Efficacy of Phase I and Phase II Coxiella burnetii Bacterin Vaccines in a Pregnant Ewe Challenge Model

The bacterium Coxiella burnetii can cause the disease Q-fever in a wide range of animal hosts. Ruminants, including sheep, are thought to play a pivotal role in the transmission of C. burnetii to humans; however, the only existing livestock vaccine, namely, Coxevac® (Ceva Animal Health Ltd., Libourne, France), a killed bacterin vaccine based on phase I C. burnetii strain Nine-Mile, is only approved for use in goats and cattle. In this study, a pregnant ewe challenge model was used to determine the protective effects of Coxevac® and an experimental bacterin vaccine based on phase II C. burnetii against C. burnetii challenge. Prior to mating, ewes (n = 20 per group) were vaccinated subcutaneously with either Coxevac®, the phase II vaccine, or were unvaccinated. A subset of pregnant ewes (n = 6) from each group was then challenged 151 days later (~100 days of gestation) with 106 infectious mouse doses of C. burnetii, Nine-Mile strain RSA493. Both vaccines provided protection against C. burnetii challenge as measured by reductions in bacterial shedding in faeces, milk and vaginal mucus, and reduced abnormal pregnancies, compared to unvaccinated controls. This work highlights that the phase I vaccine Coxevac® can protect ewes against C. burnetii infection. Furthermore, the phase II vaccine provided comparable levels of protection and may offer a safer and cost-effective alternative to the currently licensed vaccine.

Comparative analysis of swine leukocyte antigen gene diversity in European farmed pigs

In Europe, swine represent economically important farm animals and furthermore have become a preferred preclinical large animal model for biomedical studies, transplantation and regenerative medicine research. The need for typing of the swine leukocyte antigen (SLA) is increasing with the expanded use of pigs as models for human diseases and organ‐transplantation experiments and their use in infection studies and for design of veterinary vaccines. In this study, we characterised the SLA class I (SLA‐1, SLA‐2, SLA‐3) and class II (DRB1, DQB1, DQA) genes of 549 farmed pigs representing nine commercial pig lines by low‐resolution (Lr) SLA haplotyping. In total, 50 class I and 37 class II haplotypes were identified in the studied cohort. The most common SLA class I haplotypes Lr‐04.0 (SLA‐1*04XX‐SLA‐3*04XX(04:04)‐SLA‐2*04XX) and Lr‐32.0 (SLA‐1*07XX‐SLA‐3*04XX(04:04)‐SLA‐2*02XX) occurred at frequencies of 11.02 and 8.20% respectively. For SLA class II, the most prevalent haplotypes Lr‐0.15b (DRB1*04XX(04:05/04:06)‐DQB1*02XX(02:02)‐DQA*02XX) and Lr‐0.12 (DRB1*06XX‐DQB1*07XX‐DQA*01XX) occurred at frequencies of 14.37 and 12.46% respectively. Meanwhile, our laboratory has contributed to several vaccine correlation studies (e.g. Porcine Reproductive and Respiratory Syndrome Virus, Classical Swine Fever Virus, Foot‐and‐Mouth Disease Virus and Swine Influenza A Virus) elucidating the immunodominance in the T‐cell response with antigen specificity dependent on certain SLA‐I and SLA‐II haplotypes. Moreover, these SLA–immune response correlations could facilitate tailored vaccine development, as SLA‐I Lr‐04.0 and Lr‐32.0 as well as SLA‐II Lr‐0.15b and Lr‐0.12 are highly abundant haplotypes in European farmed pigs.

Diversity of the Swine Leukocyte Antigen Class I and II in Commercial Pig Populations

Among swine genetic markers, the highly polymorphic swine leukocyte antigen (SLA) is one of the key determinants, associated with not only immune responses but also reproductive performance and meat quality. The objective of this study was to characterize the SLA class I and II diversities in the commercial pig populations. In this study, a total number of 158 pigs (126 gilts and 32 boars) were randomly selected from different breeding herds of five major pig-producing companies, which covered ~70% of Thai swine production. The results indicate that a moderate level of SLA diversity was maintained in the Thai swine population, despite the performance-oriented breeding scheme. The highly common SLA class I alleles were SLA-1^*08:XX, SLA-2^*02:XX, and SLA-3^*04:XX at a combined frequency of 30.1, 18.4, and 34.5%, respectively, whereas DRB1^*04:XX, DQB1^*02:XX and DQA^*02:XX were the common class II alleles at 22.8, 33.3, and 38.6%, respectively. The haplotype Lr-32.0 (SLA-1^*07:XX, SLA-2^*02:XX, and SLA-3^*04:XX) and Lr-0.23 (DRB1^*10:XX, DQB1^*06:XX, DQA^* 01:XX) was the most common SLA class I and II haplotype, at 15.5 and 14.6%, respectively. Common class I and II haplotypes were also observed, which Lr-22.15 was the most predominant at 11.1%, followed by Lr-32.12 and Lr-4.2 at 10.8 and 7.9%, respectively. To our knowledge, this is the first report of SLA class I and II diversities in the commercial pigs in Southeast Asia. The information of the common SLA allele(s) in the population could facilitate swine genetic improvement and future vaccine design.

Duration of protection and humoral immunity induced by an adenovirus-vectored subunit vaccine for foot-and-mouth disease (FMD) in Holstein steers

Foot-and-mouth disease (FMD) is a highly contagious viral infection of cloven hooved animals that continues to cause economic disruption in both endemic countries or when introduced into a formally FMD free country. Vaccines that protect against clinical disease and virus shedding are critical to control FMD. The replication deficient human adenovirus serotype 5 (Ad5) vaccine vector expressing empty FMD virus (FMDV) capsid, AdtFMD, is a promising new vaccine platform. With no shedding or spreading of viral vector detected in field trials, this vaccine is very safe to manufacture, as there is no requirement for high containment faciitites. Here, we describe three studies assessing the proportion of animals protected from clinical vesicular disease (foot lesions) following live-FMDV challenge by intradermolingual inoculation at 6 or 9 months following a single vaccination with the commercial AdtFMD vaccine, provisionally licensed for cattle in the United States. Further, we tested the effect of vaccination route (transdermal, intramuscular, subcutaneous) on clinical outcome and humoral immunity. Results demonstrate that a single dose vaccination in cattle with the commercial vaccine vector expressing capsid proteins of the FMDV strain A24 Cruzeiro (Adt.A24), induced protection against clinical FMD at 6 months (100% transdermal, 80% intramuscular, and 60% subcutaneous) that waned by 9 months post-vaccination (33% transdermal and 20% intramuscular). Post-vaccination serum from immunized cattle (all studies) generally contained FMDV specific neutralizing antibodies by day 14. Anti-FMDV antibody secreting cells are detected in peripheral blood early following vaccination, but are absent after 28 days post-vaccination. Thus, the decay in antibody mediated immunity over time is likely a function of FMDV-specific antibody half-life. These data reveal the short time span of anti-FMDV antibody secreting cells (ASCs) and important performance characteristics of needle-free vaccination with a recombinant vectored subunit vaccine for FMDV.

Enhanced sensitivity in detection of antiviral antibody responses using biotinylation of foot-and-mouth disease virus (FMDV) capsids

Analysis of the immune response to infection of livestock by foot-and-mouth disease virus (FMDV) is most often reported as the serum antibody response to the virus. While measurement of neutralizing antibody has been sensitive and specific, measurements of the quality of the antibody response are less robust. Determining the immunoglobulin (Ig) isotype of the serum antibody response provides a deeper understanding of the biology of the response and more sensitive methods for these assays will facilitate analyses of B cell mediated immunity. We tested the hypothesis that using the virus as the molecular probe could be achieved by adding tags to the surface of the FMDV capsid, and that would enhance sensitivity in assays for anti-FMDV antibody responses. The use of a FLAG-tagged virus in these assays failed to yield improvement whereas chemically biotinylating the virus capsid resulted in significant enhancement of the signal. Here we describe methods using biotinylated virus for measuring anti-viral antibody in serum and antibody secreting cells (ASCs) in blood that are sensitive and specific. Finally, we describe using the biotinylated virus in flow cytometry where such assays should greatly enhance the analysis of anti-virus antibody producing B cells, allowing the investigator to focus on only the FMDV specific B cells when analyzing the development of the B cell response to either infection or vaccination.

Systemic immune response and virus persistence after foot-and-mouth disease virus infection of naïve cattle and cattle vaccinated with a homologous adenovirus-vectored vaccine

Background

In order to investigate host factors associated with the establishment of persistent foot-and-mouth disease virus (FMDV) infection, the systemic response to vaccination and challenge was studied in 47 steers. Eighteen steers that had received a recombinant FMDV A vaccine 2 weeks earlier and 29 non-vaccinated steers were challenged by intra-nasopharyngeal deposition of FMDV A24. For up to 35 days after challenge, host factors including complete blood counts with T lymphocyte subsets, type I/III interferon (IFN) activity, neutralizing and total FMDV-specific antibody titers in serum, as well as antibody-secreting cells (in 6 non-vaccinated animals) were characterized in the context of viral infection dynamics.

Results

Vaccination generally induced a strong antibody response. There was a transient peak of FMDV-specific serum IgM in non-vaccinated animals after challenge, while IgM levels in vaccinated animals did not increase further. Both groups had a lasting increase of specific IgG and neutralizing antibody after challenge.

Substantial systemic IFN activity in non-vaccinated animals coincided with viremia, and no IFN or viremia was detected in vaccinated animals. After challenge, circulating lymphocytes decreased in non-vaccinated animals, coincident with viremia, IFN activity, and clinical disease, whereas lymphocyte and monocyte counts in vaccinated animals were unaffected by vaccination but transiently increased after challenge. The CD4⁺/CD8⁺ T cell ratio in non-vaccinated animals increased during acute infection, driven by an absolute decrease of CD8⁺ cells.

Conclusions

The incidence of FMDV persistence was 61.5 % in non-vaccinated and 54.5 % in vaccinated animals. Overall, the systemic factors examined were not associated with the FMDV carrier/non-carrier divergence; however, significant differences were identified between responses of non-vaccinated and vaccinated cattle.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-016-0838-x) contains supplementary material, which is available to authorized users.

Expanding specificity of class I restricted CD8+ T cells for viral epitopes following multiple inoculations of swine with a human adenovirus vectored foot-and-mouth disease virus (FMDV) vaccine

The immune response to the highly acute foot-and-mouth disease virus (FMDV) is routinely reported as a measure of serum antibody. However, a critical effector function of immune responses combating viral infection of mammals is the cytotoxic T lymphocyte (CTL) response mediated by virus specific CD8 expressing T cells. This immune mechanism arrests viral spread by killing virus infected cells before new, mature virus can develop. We have previously shown that infection of swine by FMDV results in a measurable CTL response and have correlated CTL killing of virus-infected cells with specific class I major histocompatibility complex (MHC) tetramer staining. We also showed that a modified replication defective human adenovirus 5 vector expressing the FMDV structural proteins (Ad5-FMDV-T vaccine) targets the induction of a CD8⁺ CTL response with a minimal humoral response. In this report, we show that the specificity of the CD8⁺ T cell response to Ad5-FMDV-T varies between cohorts of genetically identical animals. Further, we demonstrate epitope specificity of CD8⁺ T cells expands following multiple immunizations with this vaccine.

Effect of Foot-and-Mouth Disease Virus Infection on the Frequency, Phenotype and Function of Circulating Dendritic Cells in Cattle

Foot-and-mouth disease virus (FMDV) is a highly contagious virus that causes one of the most devastating diseases in cloven-hoofed animals. Disease symptoms develop within 2 to 3 days of exposure and include fever and vesicular lesions on the tongue and hooves. Dendritic cells (DC) play an essential role in protective immune responses against pathogens. Therefore, investigating their role during FMDV infection would lead to a better understanding of host-pathogen interactions. In this study, following infection of cattle with FMDV, we investigated the frequency and function of conventional (cDC) and plasmacytoid DC (pDC) in blood by using multi-color flow cytometry. We show that the frequency of cDC and pDC increased following FMDV infection and peaked 3 to 4 days post-infection. During peak viremia, the cattle became lymphopenic, the expression of MHC class II molecules on cDC and pDC was dramatically down-regulated, the processing of exogenous antigen by cDC and pDC was impaired, and there was an increase in IL-10 production by DC and monocytes. Notably, after clearance of FMDV from the blood, MHC class II expression returned to pre-infection levels. Altogether, our study demonstrates that in cattle, FMDV inhibits the function of DC, thereby retarding the initiation of adaptive immune responses, potentially enhancing virus shedding during the acute phase of infection.

Characterization of binding specificities of bovine leucocyte class I molecules: impacts for rational epitope discovery

The binding of peptides to classical major histocompatibility complex (MHC) class I proteins is the single most selective step in antigen presentation. However, the peptide-binding specificity of cattle MHC (bovine leucocyte antigen, BoLA) class I (BoLA-I) molecules remains poorly characterized. Here, we demonstrate how a combination of high-throughput assays using positional scanning combinatorial peptide libraries, peptide dissociation, and peptide-binding affinity binding measurements can be combined with bioinformatics to effectively characterize the functionality of BoLA-I molecules. Using this strategy, we characterized eight BoLA-I molecules, and found the peptide specificity to resemble that of human MHC-I molecules with primary anchors most often at P2 and P9, and occasional auxiliary P1/P3/P5/P6 anchors. We analyzed nine reported CTL epitopes from Theileria parva, and in eight cases, stable and high affinity binding was confirmed. A set of peptides were tested for binding affinity to the eight BoLA proteins and used to refine the predictors of peptide-MHC binding NetMHC and NetMHCpan. The inclusion of BoLA-specific peptide-binding data led to a significant improvement in prediction accuracy for reported T. parva CTL epitopes. For reported CTL epitopes with weak or no predicted binding, these refined prediction methods suggested presence of nested minimal epitopes with high-predicted binding affinity. The enhanced affinity of the alternative peptides was in all cases confirmed experimentally. This study demonstrates how biochemical high-throughput assays combined with immunoinformatics can be used to characterize the peptide-binding motifs of BoLA-I molecules, boosting performance of MHC peptide-binding prediction methods, and empowering rational epitope discovery in cattle.

Phenotypic, ultra-structural, and functional characterization of bovine peripheral blood dendritic cell subsets

Dendritic cells (DC) are multi-functional cells that bridge the gap between innate and adaptive immune systems. In bovine, significant information is lacking on the precise identity and role of peripheral blood DC subsets. In this study, we identify and characterize bovine peripheral blood DC subsets directly ex vivo, without further in vitro manipulation. Multi-color flow cytometric analysis revealed that three DC subsets could be identified. Bovine plasmacytoid DC were phenotypically identified by a unique pattern of cell surface protein expression including CD4, exhibited an extensive endoplasmic reticulum and Golgi apparatus, efficiently internalized and degraded exogenous antigen, and were the only peripheral blood cells specialized in the production of type I IFN following activation with Toll-like receptor (TLR) agonists. Conventional DC were identified by expression of a different pattern of cell surface proteins including CD11c, MHC class II, and CD80, among others, the display of extensive dendritic protrusions on their plasma membrane, expression of very high levels of MHC class II and co-stimulatory molecules, efficient internalization and degradation of exogenous antigen, and ready production of detectable levels of TNF-alpha in response to TLR activation. Our investigations also revealed a third novel DC subset that may be a precursor of conventional DC that were MHC class II⁺ and CD11c⁻. These cells exhibited a smooth plasma membrane with a rounded nucleus, produced TNF-alpha in response to TLR-activation (albeit lower than CD11c⁺ DC), and were the least efficient in internalization/degradation of exogenous antigen. These studies define three bovine blood DC subsets with distinct phenotypic and functional characteristics which can be analyzed during immune responses to pathogens and vaccinations of cattle.

Characterization of cytotoxic T lymphocyte function after foot-and-mouth disease virus infection and vaccination

The induction of neutralizing antibodies specific for foot-and-mouth disease virus (FMDV) has been the central goal of vaccination efforts against this economically important disease of cloven-hoofed animals. Although these efforts have yielded much success, challenges remain, including little cross-serotype protection and inadequate duration of immunity. Commonly, viral infections are characterized by induction of cytotoxic T lymphocytes (CTL), yet the function of CTL in FMDV immunity is poorly defined. We developed an assay for detection of CTL specific for FMDV and reported that a modified adenovirus-vectored FMDV vaccine could induce CTL activity. This allowed us to determine whether FMDV-specific CTL responses are induced during infection and to test further whether vaccine-induced CTL could protect against challenge with FMDV. We now show the induction of antigen-specific CTL responses after infection of swine with FMDV strain A24 Cruizero. In addition, we developed a vaccination strategy that induces FMDV-specific CTL in the absence of significant neutralizing antibody. Animals vaccinated using this protocol showed delayed clinical disease and significantly suppressed viremia compared to control animals, suggesting a role for CTLs in the control of virus shedding. These results provide new insights showing induction of CTL responses to FMDV following infection or vaccination, and create the potential for improving vaccine performance by targeting cellular immunity.

Identification of peptides from foot-and-mouth disease virus structural proteins bound by class I swine leukocyte antigen (SLA) alleles, SLA-1*0401 and SLA-2*0401

Characterization of the peptide-binding specificity of swine leukocyte antigen (SLA) class I and II molecules is critical to the understanding of adaptive immune responses of swine toward infectious pathogens. Here, we describe the complete binding motif of the SLA-2*0401 molecule based on a positional scanning combinatorial peptide library approach. By combining this binding motif with data achieved by applying the NetMHCpan peptide prediction algorithm to both SLA-1*0401 and SLA-2*0401, we identified high-affinity binding peptides. A total of 727 different 9mer and 726 different 10mer peptides within the structural proteins of foot-and-mouth disease virus (FMDV), strain A24 were analyzed as candidate T-cell epitopes. Peptides predicted by the NetMHCpan were tested in ELISA for binding to the SLA-1*0401 and SLA-2*0401 major histocompatibility complex class I proteins. Four of the 10 predicted FMDV peptides bound to SLA-2*0401, whereas five of the nine predicted FMDV peptides bound to SLA-1*0401. These methods provide the characterization of T-cell epitopes in response to pathogens in more detail. The development of such approaches to analyze vaccine performance will contribute to a more accelerated improvement of livestock vaccines by virtue of identifying and focusing analysis on bona fide T-cell epitopes.

Porcine major histocompatibility complex (MHC) class I molecules and analysis of their peptide-binding specificities

In all vertebrate animals, CD8⁺ cytotoxic T lymphocytes (CTLs) are controlled by major histocompatibility complex class I (MHC-I) molecules. These are highly polymorphic peptide receptors selecting and presenting endogenously derived epitopes to circulating CTLs. The polymorphism of the MHC effectively individualizes the immune response of each member of the species. We have recently developed efficient methods to generate recombinant human MHC-I (also known as human leukocyte antigen class I, HLA-I) molecules, accompanying peptide-binding assays and predictors, and HLA tetramers for specific CTL staining and manipulation. This has enabled a complete mapping of all HLA-I specificities (“the Human MHC Project”). Here, we demonstrate that these approaches can be applied to other species. We systematically transferred domains of the frequently expressed swine MHC-I molecule, SLA-1*0401, onto a HLA-I molecule (HLA-A*11:01), thereby generating recombinant human/swine chimeric MHC-I molecules as well as the intact SLA-1*0401 molecule. Biochemical peptide-binding assays and positional scanning combinatorial peptide libraries were used to analyze the peptide-binding motifs of these molecules. A pan-specific predictor of peptide–MHC-I binding, NetMHCpan, which was originally developed to cover the binding specificities of all known HLA-I molecules, was successfully used to predict the specificities of the SLA-1*0401 molecule as well as the porcine/human chimeric MHC-I molecules. These data indicate that it is possible to extend the biochemical and bioinformatics tools of the Human MHC Project to other vertebrate species.

Evidence of activation and suppression during the early immune response to foot-and-mouth disease virus

Foot-and-mouth disease virus causes a serious disease of livestock species, threatening free global trade and food security. The disease spreads rapidly between animals, and to ensure a window of opportunity for such spread, the virus has evolved multiple mechanisms to subvert the early immune response. The cycle of infection in the individual animal is very short, infection is initiated, disseminated throughout the body and infectious virus produced in <7 days. Foot-and-mouth disease virus has been shown to disrupt the innate response in vitro and also interacts directly with antigen-presenting cells and their precursors. This interaction results in suboptimal immune function, favouring viral replication and the delayed onset of specific adaptive T-cell responses. Detailed understanding of this cycle is crucial to effectively control disease in livestock populations. Knowledge-based vaccine design would specifically target and induce the immunological mechanisms of early protection and of robust memory induction. Specifically, information on the contribution of cytokines and interferon, innate immune cells as well as humoral and cellular immunity can be employed to design vaccines promoting such responses. Furthermore, understanding of viral escape mechanisms of immunity can be used to create attenuated viruses that could be used to develop novel vaccines and to study viral pathogenesis.

Rapid and transient activation of γδ T cells to IFN-γ production, NK cell-like killing, and antigen processing during acute virus infection

γδ T cells are the majority peripheral blood T cells in young cattle. The role of γδ T cells in innate responses against infection with foot-and-mouth disease virus was analyzed on consecutive 5 d following infection. Before infection, bovine WC1(+) γδ T cells expressed a nonactivated phenotype relative to CD62L, CD45RO, and CD25 expression and did not produce IFN-γ ex vivo. Additionally, CD335 expression was lacking and no spontaneous target cell lysis could be detected in vitro, although perforin was detectable at a very low level. MHC class II and CD13 expression were also lacking. Following infection with foot-and-mouth disease virus, expression of CD62L and CD45RO was greatly reduced on WC1(+) γδ T cells, and unexpectedly, CD45RO expression did not recover. A transient increase in expression of CD25 correlated with production of IFN-γ. Expression of CD335 and production of perforin were detected on a subset of γδ T cells, and this correlated with an increased spontaneous killing of xenogeneic target cells. Furthermore, increased MHC class II expression was detected on WC1(+) γδ T cells, and these cells processed protein Ags. These activities are rapidly induced, within 3 d, and wane by 5 d following infection. All of these functions, NK-like killing, Ag processing, and IFN-γ production, have been demonstrated for these cells in various species. However, these results are unique in that all these functions are detected in the same samples of WC1(+) γδ T cells, suggesting a pivotal role of these cells in controlling virus infection.

Activation of porcine natural killer cells and lysis of foot-and-mouth disease virus infected cells

Natural killer (NK) cells play a vital role in innate response against viral infections and cellular transformation. In vivo modulation of their response may enhance their antiviral function. Here we describe the phenotype of porcine NK cells, test potential proinflammatory cytokines for activation of these cells and assess the capability of porcine NK cells to kill virus-infected or tumor cells in vitro. The CD2+/CD8+/CD3(-) cell compartment contained porcine NK cells, which at the resting stage were minimally cytotoxic toward foot-and-mouth disease virus (FMDV)-infected porcine cells or tumor cell lines. Direct stimulation of NK cells with proinflammatory cytokines induced efficient lysis of FMDV-infected cells with interleukin (IL)-2 or IL-15 showing the highest stimulatory capacity. Lower levels of NK cell activation were induced by IL-12, IL-18, or interferon (IFN)-alpha, however, IL-12 and IL-18 synergistically activated NK cells. Combinations of IL-15 and IL-12 or IL-15 and IL-18 did not further increase the porcine NK cell lytic capability over IL-15 alone. Natural killer cells expressed IFN-gamma regardless of the cytokine used for stimulation while expression of perforin increased modestly. The enhancement of porcine NK cell activity by proinflammatory cytokines offers a promising tool for development of antiviral approaches against virus infection.

Loss of plasmacytoid dendritic cell function coincides with lymphopenia and viremia during foot-and-mouth disease virus infection

Foot-and-mouth disease virus (FMDV) causes an acute, highly contagious disease of livestock. Though FMDV is very sensitive to interferon-alpha (IFN-alpha), IFN-beta, and IFN-gamma, the virus has evolved mechanisms to evade such innate responses. For instance, during acute infection, FMDV suppresses IFN-alpha production by skin and myeloid dendritic cells (DCs). We have previously reported that FMDV infection induces a transient lymphopenia and interruption of T-lymphocyte responses to mitogenic stimuli. To further understand the immunopathogenesis of FMD, we have now analyzed the serum IFN-alpha response in relation to lymphopenia, and the number and function of plasmacytoid DCs (pDCs) following infection of pigs with multiple serotypes of FMDV. Serum IFN-alpha peaked 2-3 d post-infection (PI), regardless of FMDV serotype. Lymphopenia coincided with peak viremia and the serum IFN-alpha response. Circulating pDC numbers and in-vitro pDC IFN-alpha secretion transiently declined by 48 h following infection. Infection of lymphocytes or pDCs was never detected regardless of the FMDV serotype inoculated or the age of the animal infected. These data indicate that, like other DC subsets, there is suppression of interferon production by pDCs, which abrogates this important innate response. Rapid induction of serum IFN-alpha, albeit short-lived, may contribute to the rapid resolution of FMDV viremia prior to induction of specific immunity.

Immune evasion during foot-and-mouth disease virus infection of swine

Summary: The interface between successful pathogens and their hosts is often a tenuous balance. In acute viral infections, this balance involves induction and inhibition of innate responses. Foot‐and‐mouth disease virus (FMDV) is considered one of the most contagious viruses known and is characterized by rapid induction of clinical disease in cloven hoofed animals exposed to infection. Viral shedding is extensive before the equally rapid resolution of acute disease. This positive strand RNA virus is an extremely successful pathogen, due in part to the ability to interrupt the innate immune response. Previous reviews have described the inhibition of cellular innate responses in the infected cell both in vitro and in vivo. Here, we present a review of virus inhibition of cells that are a source of antiviral function in swine. Particularly in the case of dendritic cells and natural killer cells, the virus has evolved mechanisms to interrupt the normal function of these important mediators of innate function, even though these cells are not infected by the virus. Understanding how this virus subverts the innate response will provide valuable information for the development of rapidly acting biotherapeutics to use in response to an outbreak of FMDV.

Ad5 delivery of IL-15 enhances porcine natural killer cell activity (81.11)

Foot-and-mouth disease virus (FMDV) is a highly infectious picornavirus that causes disease in cloven-hoofed animals, and remains an international economic threat to the livestock industry. Although a protective killed-virus vaccine exists, its utility is limited by the window of susceptibility present between vaccination and the induction of adaptive immunity. Natural killer (NK) cells play an important role in innate immunity by eliminating virus-infected cells. We have previously shown that interleukin-15 (IL-15) plays a critical role in the development, maintenance, and activation of NK cells in swine, and represents a potential method for improving porcine NK cell killing activity. We have constructed a replication-defective human Ad5 vector expressing the gene for porcine IL-15 (Ad5-pIL-15). Culture supernatants of cells infected with Ad5-pIL-15 were capable of stimulating porcine NK cells in vitro as indicated by elevated target cell killing. This suggests that Ad5-pIL-15 has the potential to stimulate porcine NK cell killing activity in vivo. Further experiments will focus on Ad5-pIL-15 and whether it can inhibit FMDV pathogenesis in pigs.

Evaluation of granulysin and perforin as candidate biomarkers for protection following vaccination with Mycobacterium bovis BCG or M. bovis delta-RD1 (81.10)

Development of improved vaccines against tuberculosis (TB) is directly correlated to the investigation of new and better correlates of protection after vaccination. We examined the kinetics of granulysin, perforin, IFN-gamma and Fas-L responses to M. bovis purified protein derivative (PPD) stimulation by peripheral blood mononuclear cells from BCG- and non-vaccinated cattle. Gene expression profiles following PPD stimulation showed significant increases in transcripts for granulysin and IFN-gamma in both CD4+ and CD8+ T cells in BCG-vaccinated as compared to non-vaccinated animals. Perforin & IFN-gamma examined by flow cytometry, showed a difference of 1-2% more PPD-specific cells in BCG-vaccinated than non-vaccinated animals. In a second trial, M. bovis BCG vaccinated animals had lower disease and pathological scores as compared to M. bovis Delta-RD1(a new vaccinate candidate) and the control group. Gene expression of granulysin and perforin were significantly increased in both vaccine groups (M. bovis BCG and M. bovis Delta-RD1 vaccinated) as compared to control after vaccination and challenge. IFN-gamma expression was increased only after vaccination and secretion was higher in the control, as compared to both vaccine groups demonstrating no correlation with protection upon vaccination.

Bovine γδ T cell response in foot-and-mouth disease virus infection (FMDV) (81.12)

In cattle, ?d T cells are a major population of the peripheral blood T cells but there is no precise description of their role in viral infections. We examined the phenotype and function of bovine ?d T cells during infection with FMDV. The early phase of infection was examined to test for a possible role for ?d T cells in innate responses against FMDV. Gamma delta T cells were sorted from PBMC of naïve or FMDV infected Holstein calves. The cells from naive animals highly expressed CD62 and CD45RO and about 50% expressed CD25, but not CD335. Gamma delta T cells did not produce IFNγ and no lytic activity could be demonstrated against a tumor cell target in vitro, although a very low level of perforin was detected. Cells from infected animals had phenotypic alterations on γd T cells between 2 and 6 days post infection (dpi). Expression of CD62 and CD45RO was down regulated and CD25 expression moderately increased. Unexpectedly, CD13 was expressed on days 2 and 3 after infection and were cytolytic against K562 cells. In addition, γδ cells isolated on these days expressed CD335, perforin and produced IFNγ. However, the isolated γd T cells produced less IFNγ and expressed less perforin compared to γd T cells assayed from non-sorted PBMC, indicating that the function of γd T cells may depend on factors derived from other cells. Overall, bovine γd T cells are activated upon infection with FMDV and adopt NK cell phenotypical and functional properties. Therefore, bovine γd T cells may likely participate in the innate response to infection with FMDV and targeting activation of γδ T cells could lead to rapid protection against FMDV infection.

Langerhans cells in porcine skin

Langerhans cells (LCs) are resident dendritic cells (DCs) of skin and mucosal epithelium. The standard for identifying skin DCs as LCs is expression of langerin (CD207), a surface protein that mediates Birbeck granule (BG) formation upon internalization. Reports of BGs in porcine skin DC are contradictory, due to lack of langerin detection. Here, we present the sequence of porcine langerin/CD207, showing that the predicted porcine protein shares 75%/86% amino acid identity/similarity with human. Langerin mRNA was detected in porcine skin DCs by PCR and langerin protein was detected in both isolated skin DCs and skin sections by immunostaining. Approximately, 50-70% of skin DCs expressed langerin, demonstrating that the majority of porcine skin DCs are LCs. The full length sequence combined with the identification of antibodies reactive with porcine langerin, facilitates the study of LCs in swine, and advances the use of swine for studying skin diseases and infectious disease processes involving skin.

Natural Killer cell function during foot-and-mouth disease virus infection (46.19)

Foot-and-mouth disease (FMD) is a highly contagious disease of cloven-hoofed animals. Immunological knowledge to assess more rapid acting vaccines against FMDV is presently limited. We examined the reactivity of swine and cattle NK cells following infection for their capability to express intracellular perforin, to kill a human tumor cell line target in vitro, and to secret IFN gamma. The cytotoxicity of NK cells from non-infected animals against the K562 cells is low with baseline levels at 5–15% in swine and 15–20% in cattle. Stimulation with rhIL-2 or rhIL-12 plus rhIL-15, increased the lytic activity against K562 cells. Infection with FMDV inhibited swine NK cell lytic activity but did not significantly increase IFN gamma secretion during the acute infection. Perforin expression increased but this did not correlate with the killing capability of the swine NK cells. Infection of cattle with FMDV initially activated the NK cells to increase target cell lysis. NK cell IFN gamma secretion and perforin expression were slightly elevated upon infection and coincided with the lytic activity in cattle. These results are a further indication of immune evasion by FMDV by inhibiting or limiting NK cell function. The potential to manipulate the innate immune response to block this evasion is discussed in the context of designing rapid acting vaccines for foot-and-mouth disease.

Evasion of the innate response of circulating DC populations by foot-and-mouth disease virus (46.6)

The evolution among viruses of multiple mechanisms to evade the innate immune response, particularly the actions of interferons, has been described for FMDV infected cells. However, mechanisms involving the response of cells of the innate immune system, especially uninfected cells, are not well understood. Here we report the analysis of IFN producing dendritic cell subsets of PBMC. When pigs were infected with two serotypes of FMDV, viremia developed and serum IFNa peaked at 2–3 days after inoculation. IFNa in serum is no longer detectable 4 to 5 days post infection. The IFNa response to CpG of plasmacytoid dendtritic cells (pDC) was significantly diminished. In addition, monocyte derived dendritic cells (MoDC) of pigs produce IFNa in response to poly I:C but not CpG. During FMDV infection, the MoDC response to poly I:C stimulation is blocked with similar kinetics to viral inhibition of pDC. Analysis shows no infection of PBMC taken from these animals. We propose that this virus has evolved a mechanism to shut down the IFNa response of DC in the periphery. The virus induces a rapid IFN response from dendritic cells which is then blocked by anti-inflammatory signals from viral infected cells. This skews the balance of the host/pathogen interaction in favor of lateral viral spread during acute infection. We are currently evaluating potential mechanisms by which the virus blocks cytokine responses in non-infected cells.

Vesicular stomatitis New Jersey virus (VSNJV) infects keratinocytes and is restricted to lesion sites and local lymph nodes in the bovine, a natural host

Inoculation of vesicular stomatitis New Jersey virus (VSNJV) by skin scarification of the coronary-band in cattle, a natural host of VSNJV, resulted in vesicular lesions and 6-8 log(10) TCID(50) increase in skin virus titers over a 72 h period. Virus infection was restricted to the lesion sites and lymph nodes draining those areas but no virus or viral RNA was found in the blood or in 20 other organs and tissues sampled at necropsy. Scarification of flank skin did not result in lesions or a significant increase in viral titer indicating that viral clinical infection is restricted to skin inoculation at sites where lesions naturally occur. Viral antigens co-localized primarily with keratinocytes in the coronary band, suggesting these cells are the primary site of viral replication. Viral antigen also co-localized with few MHC-II positive cells, but no co-localization was observed in cells positive for macrophage markers. Although granulocyte infiltration was observed in lesions, little viral antigen co-localized with these cells. This is the first detailed description of VSNJV tissue distribution and infected cell characterization in a natural host. The pathogenesis model shown herein could be useful for in-vivo tracking of virus infection and local immune responses.

IL-13 replaces IL-4 in development of monocyte derived dendritic cells (MoDC) of swine

Dendritic cells (DCs) are a critical aspect of innate immune responses in addition to initiating adaptive immunity. In vitro generation of monocyte derived dendritic cells (MoDC) by culturing cells in IL-4 and granulocyte/macrophage colony stimulating factor (GM-CSF) has been reported for multiple species including swine. However, IL-4 is not a prominent cytokine detected in the periphery of common breeds of swine such as Yorkshire pigs. In this study, we report the generation and characterization of porcine MoDC in vitro using porcine IL-13 and porcine GM-CSF. These cells have the predicted expression of Class II MHC and T cell costimulatory molecules, phagocytic capacity and the ability to process and present antigen. Critically, porcine IL-13/GM-CSF MoDC have the unique ability to stimulate a primary mixed lymphocyte response in vitro. The type I interferon response of these MoDC to poly I:C (TLR3 ligand), LPS (TLR4 ligand) and CpG (TLR9 ligand) was tested. Of these TLR agonists, LPS or CpG did not stimulate induction of type I interferons, but a strong response was observed to poly I:C. This analysis shows that the generation of MoDCs in IL-13 yields cells of equivalent phenotype and function as IL-4 generated DC. However, for swine, in vitro generation of MoDC in IL-13 is likely to induce a more physiological cell population to study given expression of IL-4 is lacking in the periphery of these animals.

A rapid, simple, and humane method for submandibular bleeding of mice using a lancet

Methods for obtaining blood samples from mice tend to be difficult, inhumane, or both. The authors describe an inexpensive, disposable, single-use lancet for submandibular bleeding of mice that allows investigators to quickly draw 0.2-0.5 ml of blood without the use of anesthesia.

Immunopotentiation of a foot-and-mouth disease virus subunit vaccine by interferon alpha

The adjuvant effect of porcine interferon alpha (pIFN-alpha) was examined in swine vaccinated with a replication-defective adenovirus containing foot-and-mouth disease virus (FMDV) A24 capsid and 3C proteinase coding regions (Ad5-A24). Groups of swine were inoculated with either high or low doses of Ad5-A24 in the presence or absence of Ad5-pIFNalpha or with a control Ad5 and challenged by intradermal inoculation in the heel bulb with FMDV at 42 days post-vaccination. After challenge all control animals developed viremia and lesions. Animals receiving low-dose Ad5-A24 had similar clinical disease, but only three of five animals developed viremia, while addition of IFN resulted in a delayed onset of lesions in three animals and only one animal had detectable viremia. Animals vaccinated with high-dose Ad5-A24 had no viremia, significantly fewer lesions and delayed onset of disease compared to the control and low-dose vaccine groups. Four of five pigs vaccinated with high-dose Ad5-A24 plus IFN were completely protected from disease and only one animal had a lesion which was restricted to the site of challenge. Thus, pIFN-alpha enhances the long-term level of protection induced by the Ad5-FMD vaccine, supporting its use as a potential adjuvant in FMD vaccination strategies.

Vaccination against foot-and-mouth disease virus confers complete clinical protection in 7 days and partial protection in 4 days: Use in emergency outbreak response

Recent outbreaks of foot-and-mouth disease virus (FMDV) demonstrate that this highly contagious viral infection of cloven hoofed animals continues to be a significant economic problem worldwide. Debate about the most effective way to respond to outbreaks of FMDV in disease free countries continues to center on the use of vaccines. In this report, we present data showing that a commercially available, standard dose vaccine formulation can fully protect cattle against direct challenge with the virus in as little as 7 days with no carrier transmission to naïve animals. Cattle challenged 4 days after vaccination have reduced disease severity, no detectable virus in blood and little virus shedding from nasal secretions. These significant effects at 4 days post vaccination, confirmed in two separate trials, support the value of using currently available vaccines as a first line of defense against foot-and-mouth disease (FMD) outbreaks.

Rapid protection of cattle from direct challenge with foot-and-mouth disease virus (FMDV) by a single inoculation with an adenovirus-vectored FMDV subunit vaccine

We have previously demonstrated that swine vaccinated with one dose of a replication-defective human adenovirus type 5 (Ad5) vector containing the capsid and 3C proteinase coding regions of foot-and-mouth disease virus (FMDV) were protected when challenged 7 days later with homologous virus. In the current study, we have extended this approach to cattle, the most economically important animals susceptible to FMD. Five cattle were vaccinated with the Ad5-FMDV subunit vaccine and these animals and 2 co-housed control animals were challenged intradermolingually 7 days later. Both control animals developed typical signs of FMD including fever and vesicular lesions on all 4 feet. All 5 vaccinated animals were protected against disseminated disease.

Granulocyte-macrophage colony-stimulating factor does not increase the potency or efficacy of a foot-and-mouth disease virus subunit vaccine

Foot-and-mouth disease (FMD) is one of the most feared diseases of livestock worldwide. Vaccination has been a very effective weapon in controlling the disease, however a number of concerns with the current vaccine including the inability of approved diagnostic tests to reliably distinguish vaccinated from infected animals and the need for high containment facilities for vaccine production, have limited its use during outbreaks in countries previously free of the disease. A number of FMD vaccine candidates have been tested and a replication-defective human adenovirus type 5 (Ad5) vector containing the FMDV capsid (P1-2A) and 3C protease coding regions has been shown to completely protect pigs against challenge with the homologous virus (FMDV A12 and A24). An Ad5-P1-2A+3C vaccine for FMDV O1 Campos (Ad5-O1C), however, only induced a low FMDV-specific neutralizing antibody response in swine potency tests. Granulocyte-macrophage colony-stimulating factor (GM-CSF) has been successfully used to stimulate the immune response in vaccine formulations against a number of diseases, including HIV, hepatitis C and B. To attempt to improve the FMDV-specific immune response induced by Ad5-O1C, we inoculated swine with Ad5-O1C and an Ad5 vector containing the gene for porcine GM-CSF (pGM-CSF). However, in the conditions used in this trial, pGM-CSF did not improve the immune response to Ad5-O1C and adversely affected the level of protection of swine challenged with homologous FMDV.

Constitutive expression of alpha interferon by skin dendritic cells confers resistance to infection by foot-and-mouth disease virus

The role of dendritic cells (DC) in the initiation of immune responses against foot-and-mouth disease virus (FMDV) is poorly understood. We analyzed the innate response of freshly isolated swine skin DC to the virus and show a rapid induction of beta interferon (IFN-beta) mRNA but not IFN-alpha mRNA. However, these DC secreted both IFN-alpha and IFN-beta proteins in response to live virus but not killed virus. Furthermore, the surface expression of swine major histocompatibility complex class II (SLA II) or CD80/CD86 molecules and antigen processing functions were not affected by FMDV exposure. Given the demonstrated sensitivity of FMDV to IFN-alpha/beta, there was no productive or nonproductive infection of these cells. Finally, freshly isolated skin DC constitutively expressed intracellular IFN-alpha protein in the absence of stimulation, with no detectable secretion of the cytokine until virus exposure. In situ analysis of these DC showed that these cells express and store IFN-alpha in uninfected animals. This is the first demonstration of the constitutive expression of IFN-alpha in resident, tissue-derived DC and indicates that skin DC can play an important role in the innate immune response of swine to viral infections.

Interactions of foot-and-mouth disease virus with soluble bovine alphaVbeta3 and alphaVbeta6 integrins

At least four members of the integrin family of receptors, alphaVbeta1, alphaVbeta3, alphaVbeta6, and alphaVbeta8, have been identified as receptors for foot-and-mouth disease virus (FMDV) in vitro. Our investigators have recently shown that the efficiency of receptor usage appears to be related to the viral serotype and may be influenced by structural differences on the viral surface (H. Duque and B. Baxt, J. Virol. 77:2500-2511, 2003). To further examine these differences, we generated soluble alphaVbeta3 and alphaVbeta6 integrins. cDNA plasmids encoding the individual complete integrin alphaV, beta3, and beta6 subunits were used to amplify sequences encoding the subunits' signal peptide and ectodomain, resulting in subunits lacking transmembrane and cytoplasmic domains. COS-1 cells were transfected with plasmids encoding the soluble alphaV subunit and either the soluble beta3 or beta6 subunit and labeled with [35S]methionine-cysteine. Complete subunit heterodimeric integrins were secreted into the medium, as determined by radioimmunoprecipitation with specific monoclonal and polyclonal antibodies. For the examination of the integrins' biological activities, stable cell lines producing the soluble integrins were generated in HEK 293A cells. In the presence of divalent cations, soluble alphaVbeta6 bound to representatives of type A or O viruses, immobilized on plastic dishes, and significantly inhibited viral replication, as determined by plaque reduction assays. In contrast, soluble alphaVbeta3 was unable to bind to immobilized virus of either serotype; however, virus bound to the immobilized integrin, suggesting that FMDV binding to alphaVbeta3 is a low-affinity interaction. In addition, soluble alphaVbeta3 did not neutralize virus infectivity. Incubation of soluble alphaVbeta6 with labeled type A12 or O1 resulted in a significant inhibition of virus adsorption to BHK cells, while soluble alphaVbeta3 caused a low (20 to 30%), but consistent, inhibition of virus adsorption. Virus incubated with soluble alphaVbeta6 had a lower sedimentation rate than native virus on sucrose density gradients, but the particles retained all of their structural proteins and still contained bound integrin and, therefore, were not exhibiting characteristics of a picornavirus A particle.

A synthetic peptide containing the consensus sequence of the G-H loop region of foot-and-mouth disease virus type-O VP1 and a promiscuous T-helper epitope induces peptide-specific antibodies but fails to protect cattle against viral challenge

A pilot study was carried out in cattle to determine the immunogenicity of a synthetic consensus peptide comprising the G-H loop region of foot-and-mouth disease virus (FMDV) type-O VP1 and a non-VP1 T-helper (Th) epitope. Cattle vaccinated intramuscularly either once (n = 5) or twice (n = 4) with 50 microg of the peptide preparation at a 21-day interval developed antibodies to the peptide as determined by ELISA with the exception of one steer that received a single dose. However, neutralizing antibody titers against FMDV type-O were modest and all animals presented with clinical FMD signs upon challenge 21 days after the last vaccination. In contrast, four of the five animals inoculated with an inactivated FMD type-O commercially prepared vaccine developed neutralizing antibodies and were fully protected against clinical disease following virus challenge 21 days post-vaccination (dpv). Nucleotide sequence comparison of the VP1 region between the challenge virus and RT-PCR products recovered from a lesion of the peptide-vaccinated animal with the highest neutralizing antibody titer 5 days post-challenge (dpc) showed no evidence for selection of a neutralization-resistant mutant. We conclude that although the synthetic peptide induced an antibody response in cattle, it failed to confer protection against FMDV challenge.

Induction of lymphopenia and inhibition of T cell function during acute infection of swine with foot and mouth disease virus (FMDV)

Foot and mouth disease virus (FMDV) is a picornavirus that causes an acute vesicular disease of cloven-hoofed animals. This virus continues to be a threat to livestock worldwide with outbreaks causing severe economic losses. The present study shows an analysis of immune system phenotype and function during the acute phase of FMDV infection in swine. In the first days of infection, a significant lymphopenia is observed that involves all T cell subsets, CD4(+), CD8(+), and CD4(+)/CD8(+). This marked lymphopenia is not a result of active infection of PBMC with the virus. Further, the response of residual peripheral blood T cells to the mitogen, Concanavalin A (ConA) is significantly reduced and occasionally eliminated. Animals usually resolve clinical signs of disease and develop antigen specific T cell responses to the virus and recover ConA reactivity. These characteristics of acute phase infection likely play an important role in viral pathogenesis, propagation and shedding of viral particles and may be targeted as a way of improving vaccine formulations.

Characterization and functional analysis of skin-derived dendritic cells from swine without a requirement for in vitro propagation

A low-density cell population was isolated from skin explants of pigs and characterized as a highly enriched dendritic cell (DC) population based on phenotypical and functional properties. The skin-derived DCs were identified by their characteristic ultrastructural properties as well as by consistent co-expression of the CD1 and SWC3a antigens that clearly differentiate them from other porcine leukocytes. These cells exhibit higher expression of porcine MHC class II (SLAII) and CD80/86 antigens as compared to macrophage/monocyte cells. They consistently expressed the S100 beta antigen at high levels and did not express the lymphoid markers CD3, CD4 or CD8. Within this population of skin-derived DCs there was variable expression of CD11c, CD14 and CD16. Functional characterization of this DC population revealed that they are efficient in uptake and processing of soluble protein antigens and in endocytosis of small (0.02 microm) but not large (2 microm) polystyrene beads. Further, these cells were efficient inducers of primary allogeneic responses and in stimulating antigen-specific and mitogen-induced proliferation and IFN gamma responses in autologous lymphocytes. This study provides important information to further characterize the cutaneous DCs and develop models to analyze the role of these cells in immune responses in vivo.

Borrelia burgdorferi-specific monoclonal antibodies derived from mice primed with Lyme disease spirochete-infected Ixodes scapularis ticks

We have generated a panel of IgG monoclonal antibodies (MAbs) directed against Borrelia burgdorferi strain B31 antigens, using a method whereby mice were primed with organisms naturally inoculated by Ixodes scapularis nymphal ticks. Western blot analysis showed that these MAbs recognized several B. burgdorferi B31 antigens, including the complement inhibitor factor H-binding proteins ErpA/I/N and ErpC. Two other MAbs were specific for the RevA protein, and have enabled characterization of that previously unknown protein. The data presented here suggest that the production of MAbs from animals infected by tick-bite is a potentially useful tool for the identification of novel proteins synthesized by B. burgdorferi during mammalian infection.

Infection with multiple strains of Borrelia burgdorferi sensu stricto in patients with Lyme disease

OBJECTIVE

To assess human skin biopsy specimens from erythema migrans lesions for the presence of infection with multiple strains of the Lyme disease spirochete, Borrelia burgdorferi.

DESIGN

Skin biopsy specimens were obtained prospectively from patients with erythema migrans. To determine allelic differences and strain identification of B burgdorferi, the biopsy specimens were analyzed by cold single-strand conformation polymorphism of an amplified fragment of the outer surface protein C (ospC) gene. Further single-strand conformation polymorphism patterns of amplified ospC genes from culture isolates were compared with polymerase chain reaction products obtained directly from erythema migrans biopsy specimens.

SETTING

A private dermatology office and a university medical center outpatient department.

PATIENTS

Sixteen patients presenting with erythema migrans.

RESULTS

Two of the 16 patients in this cohort were infected with 2 B burgdorferi sensu stricto strains, as evidenced by 2 ospC alleles in their skin biopsy results.

CONCLUSION

This is the first documented description of the existence of more than a single strain of B burgdorferi sensu stricto in a human specimen.

Four clones of Borrelia burgdorferi sensu stricto cause invasive infection in humans

Lyme disease begins at the site of a tick bite, producing a primary infection with spread of the organism to secondary sites occurring early in the course of infection. A major outer surface protein expressed by the spirochete early in infection is outer surface protein C (OspC). In Borrelia burgdorferi sensu stricto, OspC is highly variable. Based on sequence divergence, alleles of ospC can be divided into 21 major groups. To assess whether strain differences defined by ospC group are linked to invasiveness and pathogenicity, we compared the frequency distributions of major ospC groups from ticks, from the primary erythema migrans skin lesion, and from secondary sites, principally from blood and spinal fluid. The frequency distribution of ospC groups from ticks is significantly different from that from primary sites, which in turn is significantly different from that from secondary sites. The major groups A, B, I, and K had higher frequencies in the primary sites than in ticks and were the only groups found in secondary sites. We define three categories of major ospC groups: one that is common in ticks but very rarely if ever causes human disease, a second that causes only local infection at the tick bite site, and a third that causes systemic disease. The finding that all systemic B. burgdorferi sensu stricto infections are associated with four ospC groups has importance in the diagnosis, treatment, and prevention of Lyme disease.

Vector competence of Ixodes scapularis and Ixodes ricinus (Acari: Ixodidae) for three genospecies of Borrelia burgdorferi

The vector competence of 2 tick species, Ixodes ricinus (L.) and Ixodes scapularis Say, was determined and compared for 3 genospecies of Borrelia burgdorferi. The 3 genospecies of B. burgdorferi used in the following experiments were Borrelia burgdorferi sensu stricto (B-31 and B-31.D1 clone), Borrelia afzelii (strain Pgau. C3), and Borrelia garinii (strain VS286 and VSBP). Spirochetes from all 5 strains were inoculated intradermally into outbred mice; larval ticks of both species were subsequently fed on those mice and replete larvae were assayed for infection by culture in BSK-H media every 7 d for 4 wk. Infection frequencies in I. scapularis exposed to the 5 strains were as follows: B-31 (90%), B-31.D1 (83%), Pgau.C3 (87%), VS286 (10%), and VSBP (5%). The comparable infection frequencies for I. ricinus were B-31 (3%), B-31.D1 (3%), Pgau.C3 (90%), VS286 (5%), and VSBP (3%). Resultant nymphal I. scapularis successfully transmitted B-31, B-31,D1, Pgau.C3, and VS286 to outbred mice. I. ricinus nymphs transmitted Pgau.C3 and VS286. Both species failed to transmit strain VSBP.

Culture-confirmed reinfection of a person with different strains of Borrelia burgdorferi sensu stricto

In recent years, the utility of serum-based diagnostic testing for Lyme disease has improved substantially; however, recovery by culture of the bacterium from skin biopsies of suspected patients is still the only definitive laboratory test. Reinfection of patients has been assumed to occur but as yet has not been documented by serial isolates from the same person. We present a case of culture-confirmed reinfection of a patient in Menominee County, Michigan. Borrelia burgdorferi was isolated from the skin punch biopsy specimens during each episode of erythema migrans (EM) and was subjected to molecular strain typing, genetic analysis of two outer surface protein genes, protein profile analysis, and serum antibody response testing. Results show that these isolates are distinct strains of the bacterium and that the two episodes of EM were caused by independent infections. This report describes the documented, culture-confirmed reinfection of a human by two different strains of B. burgdorferi.

Duration of immunity to reinfection with tick-transmitted Borrelia burgdorferi in naturally infected mice

The ability of naturally infected and cured mice to resist reinfection with tick-transmitted Borrelia burgdorferi was tested over a 1-year period. All of the mice were resistant to reinfection when they were challenged at 1.5 months after cure. The majority of animals were resistant to reinfection for up to 10.5 months after cure, but this resistance was lost at 1 year after cure. Both protected and unprotected animals showed a diverse array of antibodies on Western immunoblots. Protection was not associated with the killing of spirochetes in ticks, and naturally infected mice produced no antibodies to outer surface protein A (OSP A). The titers to whole Borrelia sonicate and OSP C, however, remained high throughout the 1-year study period. The levels of borreliacidal antibodies were highest in the 1.5 month-after-cure group. Natural immunity to reinfection with B. burgdorferi is limited in time, is complex, and may involve both humoral and cellular components.

Vector competence of Ixodes scapularis, I. spinipalpis, and Dermacentor andersoni (Acari:Ixodidae) in transmitting Borrelia burgdorferi, the etiologic agent of Lyme disease

This report describes the vector competence of 3 ixodid tick species, Ixodes scapularis (Say), I. spinipalpis (Nuttall), and Dermacentor andersoni (Stiles), for Borrelia burgdorferi in Colorado. The study was based on preliminary field work performed in 6 Colorado counties, where rodents and ticks were collected and assayed for the presence of B. burgdorferi. Four of the 6 counties produced 52 rodent and 39 I. spinipalpis isolates of B. burgdorferi. Two B. burgdorferi isolates were tested under laboratory conditions and found to be infective to Imperial Cancer Research Fund (ICRF) outbred mice. The 1st, a low-passage strain originating from New York (B-31, passage 6) was used as a control, and the 2nd was isolated from ear tissue of a Neotoma mexicana (Baird) (Mexican wood rat) that was trapped in Colorado. Larvae of I. scapularis, I. spinipalpis. and D. andersoni were fed on infected mice and cultured in Barbour-Stoner-Kelly media to assay for infection at 1, 2, 3, and 4 wk after repletion. The infection rates in replete larvae. were 75, 69, and 8.5%, respectively, whereas transstadial nymphal infection rates were 80, 75, and 0%, respectively. Both I. scapularis and I. spinipalpis were shown to be competent vectors that acquired the infection from the host reservoir mice and subsequently transmitted it to naive mice. Given that I. scapularis are not found in Colorado, I. spinipalpis are restricted to the nests and burrows of rodents, and because of the semiarid environment in Colorado, the risk of human contact with B. burgdorferi appears to be low.

Reactivity with a specific epitope of outer surface protein A predicts protection from infection with the Lyme disease spirochete, Borrelia burgdorferi

The response to recombinant vaccines for Lyme disease was studied to determine serum antibody levels effective in protecting against tick-transmitted infection. Data presented here demonstrate a significant correlation between antibody to an epitope on outer surface protein A (OspA) and protection against infection with Borrelia burgdorferi in canines and mice. A competitive enzyme-linked immunosorbent assay was developed to measure antibody to a site on OspA, defined by monoclonal antibody LA-2. Comparison of LA-2 titers against infection of canines and mice following vaccination and challenge established a predicted value for LA-2 titers. The statistical relationship between serum antibody levels and protection was calculated by logistic regression analysis. The statistical model predicted that an LA-2 titer of 0.32 microg equivalents (eq) per ml correlated to an 80% predicted probability of protection for both mice and dogs. This value was used to classify mice and dogs as to their protected status at the time of tick exposure. The LA-2 cutoff titer (0.32 microg eq/ml) correctly classified all dogs (n = 13) and mice (n = 44) that failed to become infected. By contrast, 20 of 22 dogs and 28 of 31 mice with titers of less than 0.32 microg eq/ml became infected. On the basis of these results, we conclude that an LA-2 titer is a reliable indicator of immune status for estimating immune protection following use of OspA-based vaccines for B. burgdorferi sensu stricto.