Effect of Mycobacterium bovis BCG vaccination on interleukin-1 beta and RANTES mRNA expression in guinea pig cells exposed to attenuated and virulent mycobacteria

IP10 is a predictor of successful vaccine protection against paratuberculosis infection in sheep

The cell mediated immune response and ability of immune cells to migrate to the site of infection are both key aspects of protection against many pathogens. Mycobacterium avium subsp. paratuberculosis (MAP) is an intracellular pathogen and the causative agent of paratuberculosis, a chronic wasting disease of ruminants. Current commercial vaccines for paratuberculosis reduce the occurrence of clinical disease but not all animals are protected from infection. Therefore, there is a need to understand the immune responses triggered by these vaccines at the site of infection, in circulating immune cells and their relationships to vaccine-mediated protection. The magnitude and location of gene expression related to the cell mediated immune response and cellular migration were studied in the ileum of sheep. In addition, longitudinal IP10 (also known as IP10) secretion by circulating immune cells was examined in the same sheep. Animals were grouped based on vaccination status (vaccinated vs non-vaccinated) and MAP exposure (experimentally exposed vs unexposed). Vaccination of unexposed sheep increased the expression of IP10, CCL5 and COR1c. Sheep that were successfully protected by vaccination (uninfected following experimental exposure) had significantly reduced expression of IP10 in the ileum at 12 months post exposure compared to vaccine non-responders (those that became infected) and non-vaccinated infected sheep. Successfully protected sheep also had significantly increased secretion of IP10 in in vitro stimulated immune cells from whole blood compared to vaccine non responders at 4 months post exposure. Therefore, the IP10 recall response has the potential to be used as marker for infection status in vaccinated sheep and could be a biomarker for a DIVA test in sheep.

Molecular cloning, expression, and in silico structural analysis of guinea pig IL-17

Interleukin-17A (IL-17A) is a potent proinflammatory cytokine and the signature cytokine of Th17 cells, a subset which is involved in cytokine and chemokine production, neutrophil recruitment, promotion of T cell priming, and antibody production. IL-17 may play an important role in tuberculosis and other infectious diseases. In preparation for investigating its role in the highly relevant guinea pig model of pulmonary tuberculosis, we cloned guinea pig IL-17A for the first time. The complete coding sequence of the guinea pig IL-17A gene (477 nucleotides; 159 amino acids) was subcloned into a prokaryotic expression vector (pET-30a) resulting in the expression of a 17 kDa recombinant guinea pig IL-17A protein which was confirmed by mass spectrometry analysis. Homology modeling of guinea pig IL-17A revealed that the three-dimensional structure resembles that of human IL-17A. The secondary structure predicted for this protein showed the presence of one extra helix in the N-terminal region. The expression profile of IL-17A was analyzed quantitatively in spleen, lymph node, and lung cells from BCG-vaccinated guinea pigs by real-time PCR. The guinea pig IL-17A cDNA and its recombinant protein will serve as valuable tools for molecular and immunological studies in the guinea pig model of pulmonary TB and other human diseases.

Method for assessing IFN-γ responses in guinea pigs during TB vaccine trials

AIMS

We sought to develop a new method that enables the assessment of the immune response of guinea pigs during TB vaccine evaluation studies, without the need to cull or anaesthetize animals.

METHOD AND RESULTS

Guinea pigs were vaccinated with five different formulations of oral BCG. One week prior to challenge with Mycobacterium bovis, blood (50-200 μl) was taken from the ears of vaccinated subjects. Host RNA was isolated and amplified following antigenic restimulation of PBMCs for 24 h with 30 μg of bovine PPD. The up- or down-regulation of γ-interferon (IFN-γ), a key cytokine involved in protection against tuberculosis, was assessed using real-time PCR. The relative expression of prechallenge IFN-γ mRNA in the vaccinated groups (n=5) correlated (P<0·001) with protection against M. bovis challenge.

CONCLUSION

We have demonstrated that it is possible to take blood samples and track IFN-γ responses in guinea pigs that then go on to be exposed to M. bovis, thus providing prechallenge vaccine uptake information.

SIGNIFICANCE AND IMPACT OF THE STUDY

This methodology will also be applicable for tracking the immune responses of vaccinated guinea pigs over time that then go on to be challenged with M. tuberculosis during human TB vaccine evaluation studies.

Molecular cloning and expression of the IL-10 gene from guinea pigs

The Guinea pig (Cavia porcellus) is one of the most relevant small animals for modeling human tuberculosis (TB) in terms of susceptibility to low dose aerosol infection, the organization of granulomas, extrapulmonary dissemination and vaccine-induced protection. It is also considered to be a gold standard for a number of other infectious and non-infectious diseases; however, this animal model has a major disadvantage due to the lack of readily available immunological reagents. In the present study, we successfully cloned a cDNA for the critical Th2 cytokine, interleukin-10 (IL-10), from inbred Strain 2 guinea pigs using the DNA sequence information provided by the genome project. The complete open reading frame (ORF) consists of 537 base pairs which encodes a protein of 179 amino acids. This cDNA sequence exhibited 87% homology with human IL-10. Surprisingly, it showed only 84% homology with the previously published IL-10 sequence from the C4-deficient (C4D) guinea pig, leading us to clone IL-10 cDNA from the Hartley strain of guinea pig. The IL-10 gene from the Hartley strain showed 100% homology with the IL-10 sequence of Strain 2 guinea pigs. In order to validate the only published IL-10 sequence existing in Genbank reported from C4D guinea pigs, genomic DNA was isolated from tissues of C4D guinea pigs. Amplification with various sets of primers showed that the IL-10 sequence reported from C4D guinea pigs contained numerous errors. Hence the IL-10 sequence that is being reported by us replaces the earlier sequence making our IL-10 sequence to be the first one accurate from guinea pig. Recombinant guinea pig IL-10 proteins were subsequently expressed in both prokaryotic and eukaryotic cells, purified and were confirmed by N-terminal sequencing. Polyclonal anti-IL-10 antibodies were generated in rabbits using the recombinant IL-10 protein expressed in this study. Taken together, our results indicate that the DNA sequence information provided by the genome project is useful to directly clone much needed cDNAs necessary to study TB in the guinea pig. The newly cloned guinea pig IL-10 cDNA and recombinant proteins will serve as valuable resources for immunological studies in the guinea pig model of TB and other diseases.

Cloning of guinea pig IL-4: reduced IL-4 mRNA after vaccination or Mycobacterium tuberculosis infection

Interleukin-4 (IL-4), a pleiotropic cytokine produced by T-helper type 2 (Th2) cells, is involved in promoting humoral immune responses, allergic reactions and asthma. Previous studies suggested an important role for IL-4 in susceptibility to pulmonary tuberculosis; however, the role of IL-4 has not been studied in the guinea pig, a highly relevant model for this disease. In the present study, we cloned a cDNA for guinea pig IL-4 and examined, for the first time, mRNA expression by real-time RT-PCR in cultured guinea pig cells. High levels of IL-4 mRNA expression were detected in spleen T cells of naïve animals after in vitro stimulation with PMA plus ionomycin for 4-24 h. The expression of IL-4 mRNA was low in spleen and lymph node cells immunized with ovalbumin (OVA) plus Complete Freund's Adjuvant (CFA) in response to OVA (Th1), but significantly higher in the guinea pigs immunized with OVA plus alum (Th2). BCG vaccination reduced the expression of IL-4 mRNA in both spleen and lung digest cells compared to naïve guinea pigs, while levels of IFN-γ were similar in both groups. Furthermore, lung cells from Mycobacterium tuberculosis-infected guinea pigs stimulated in vitro with PPD or MPT64 showed low levels of IL-4 mRNA expression. Thus, BCG vaccination or M. tuberculosis infection modulates IL-4 mRNA expression in the guinea pig. Cloning of guinea pig IL-4 will allow us to address the role of IL-4 in vaccine-induced resistance to pulmonary TB in a highly relevant animal model.

Temporal changes in the gene signatures of BCG-vaccinated guinea pigs in response to different mycobacterial antigens

Mycobacterium bovis BCG-vaccination in the guinea pig model of tuberculosis (TB) is sufficiently protective that candidate TB vaccines are judged against this. Little is understood about how the BCG vaccine works and, in the absence of a definitive correlate of protection, it is difficult to interpret the significance of novel vaccine induced host responses. Here an extended custom-made microarray (86 guinea pig genes) was used to dissect temporal changes in BCG-vaccine induced gene signatures to different mycobacterial antigens. Initially at 4h, pro-inflammatory genes such as IL-1α, IL-1β, IL-8 and GRO were up-regulated (P<0.001) and these were then superseded by IFN-γ and GM-CSF (at 12 and 20h) post-stimulation, ex vivo with PPD. Similar genes were seen following stimulation with viable BCG but with the addition of IL-23 (P<0.01) after 8h. Our results suggest that temporal changes in the up- and down-regulation of a variety of genes are required to trigger a successful protective response to TB in guinea pigs. This provides base-line information against which new TB vaccines can be compared.

Kinetics of the immune response profile in guinea pigs after vaccination with Mycobacterium bovis BCG and infection with Mycobacterium tuberculosis

The guinea pig model of tuberculosis is used extensively in assessing novel vaccines, since Mycobacterium bovis BCG vaccination effectively prolongs survival after low-dose aerosol infection with virulent M. tuberculosis. To better understand how BCG extends time to death after pulmonary infection with M. tuberculosis, we examined cytokine responses postvaccination and recruitment of activated T cells and cytokine response postinfection. At 10 weeks postvaccination, splenic gamma interferon (IFN-gamma) mRNA was significantly elevated compared to the levels at 5 weeks in ex vivo stimulation assays. At 15, 40, 60, and 120 days postinfection, T-cell activation (CD4+ CD62Llow and CD8+ CD62Llow) and mRNA expression of IFN-gamma, tumor necrosis factor alpha (TNF-alpha), interleukin-1 (IL-1), IL-10, IL-12, and eomesodermin were assessed. Our data show that at day 40, BCG-vaccinated guinea pigs had significantly increased levels of IFN-gamma mRNA expression but decreased TNF-alpha mRNA expression in their lungs compared to the levels in nonvaccinated animals. At day 120, a time when nonvaccinated guinea pigs succumbed to infection, low levels of IFN-gamma mRNA were observed even though there were increasing levels of IL-1, IL-12, and IL-10, and the numbers of activated T cells did not differ from those in BCG-vaccinated animals. BCG vaccination conferred the advantage of recruiting greater numbers of CD4+ CD62Llow T cells at day 40, although the numbers of CD8+ CD62Llow T cells were not elevated compared to the numbers in nonvaccinated animals. Our data suggest that day 40 postinfection may be a pivotal time point in determining vaccine efficacy and prolonged survival and that BCG promotes the capacity of T cells in the lungs to respond to infection.

The guinea pig as a model of infectious diseases

The words 'guinea pig' are synonymous with scientific experimentation, but much less is known about this species than many other laboratory animals. This animal model has been used for approximately 200 y and was the first to be used in the study of infectious diseases such as tuberculosis and diphtheria. Today the guinea pig is used as a model for a number of infectious bacterial diseases, including pulmonary, sexually transmitted, ocular and aural, gastrointestinal, and other infections that threaten the lives of humans. Most studies on the immune response to these diseases, with potential therapies and vaccines, have been conducted in animal models (for example, mouse) that may have less similarity to humans because of the large number of immunologic reagents available for these other species. This review presents some of the diseases for which the guinea pig is regarded as the premier model to study infections because of its similarity to humans with regard to symptoms and immune response. Furthermore, for diseases in which guinea pigs share parallel pathogenesis of disease with humans, they are potentially the best animal model for designing treatments and vaccines. Future studies of immune regulation of these diseases, novel therapies, and preventative measures require the development of new immunologic reagents designed specifically for the guinea pig.

Biologic activity of guinea pig IFN-gamma in vitro

Interferon-gamma (IFN-gamma) plays a key role in the induction and maintenance of immunity against intracellular infectious agents. Compared to other species, little is known about the biology of this cytokine in the guinea pig (Cavia porcellus). We found that in contrast to humans and mice, IFN-gamma in the guinea pig did not induce the antiviral state, which in other species leads to protection of IFN-gamma -stimulated fibroblasts from the cytopathic effect (CPE) of subsequent viral infections. As an alternative strategy to detect and quantify guinea pig IFN-gamma activity in vitro, a reporter system using guinea pig fibroblasts transfected with a luciferase gene, which is regulated by an IFN-stimulated response element (ISRE), was established. With the help of the highly sensitive reporter assay system, the biologic activity of recombinant guinea pig IFN-gamma (GpIFN-gamma, from prokaryotic and eukaryotic expression systems was detected. The response to both native and recombinant GpIFN-gamma was inhibited by a rabbit antiserum directed against the recombinant cytokine expressed in Escherichia coli, demonstrating structural and functional homology of native and recombinant GpIFN-gamma. Stimulation with GpIFN-gamma, obtained from transfected cells, induced upregulation of MHC class I expression in a guinea pig fibroblast line. The restricted activity of GpIFN-gamma might have implications for this species' ability to control infections with intracellular pathogens.

Lung macrophages from bacille Calmette-Guérin-vaccinated guinea pigs suppress T cell proliferation but restrict intracellular growth of M. tuberculosis after recombinant guinea pig interferon-gamma activation

The guinea pig model of low-dose pulmonary tuberculosis has been used to study the pathogenesis of infection as well as the mechanisms of bacille Calmette-Guérin (BCG) vaccine-induced resistance. We investigated the function of lung cells from naive and BCG-vaccinated guinea pigs after enzymatic digestion of lung tissue with collagenase and DNase I. The total lung digest cells proliferated poorly to purified protein derivative (PPD) but comparatively better to ConA as assessed by [(3)H]-thymidine uptake. However, the non-adherent population obtained after plastic adherence of lung digests showed an enhanced response to concanavalin A (ConA) and PPD. Therefore, proliferation to ConA and PPD of nylon wool-purified T cells co-cultured with peritoneal (PMøs), alveolar (AMøs) or lung macrophages (LMøs) was assessed. Co-cultures of lung T cells and PMøs showed maximum proliferation to PPD, whereas proliferation was suppressed significantly by the addition of AMøs or LMøs. The response of T cells to ConA was unaffected in co-cultures. Incubation of co-cultures with recombinant guinea pig interferon-gamma (rgpIFN-gamma) did not reverse the suppression. In contrast, rgpIFN-gamma-treated plastic adherent LMøs that were non-specific esterase-positive were capable of reducing the intracellular growth of Mycobacterium tuberculosis. Similarly, total, non-adherent and adherent lung digest cells from BCG-vaccinated guinea pigs showed IFN-gamma and tumour necrosis factor (TNF)-alpha mRNA expression in response to ConA, lipopolysaccharide or PPD by reverse transcription-polymerase chain reaction followed by release of TNF protein but not IFN. These studies indicate that rgp-IFN-gamma-treated lung tissue macrophages from BCG-vaccinated guinea pigs are defective for inducing antigen-specific proliferation in T cells, but control the intracellular accumulation of virulent M. tuberculosis.

Unique gene expression profiles in infants vaccinated with different strains of Mycobacterium bovis bacille Calmette-Guerin

Vaccination with Mycobacterium bovis bacille Calmette-Guérin (BCG) has variable efficacy in preventing tuberculosis. We hypothesized that some of this variation might be due to differences among BCG strains. To test this, neonates in Orizaba, Mexico, were vaccinated with one of three different BCG strains (BCG-Brazil [BBCG], BCG-Denmark [DBCG], or BCG-Japan [JBCG]). One year after vaccination, peripheral blood mononuclear cells (PBMC) were obtained and recall immune responses to culture filtrate proteins (CFP) of Mycobacterium tuberculosis were evaluated using quantitative real-time PCR. CFP-activated PBMC from BBCG- and DBCG-immunized children expressed high levels of cytokines characteristic of an adaptive immune response (gamma interferon, interleukin-2beta [IL-12beta], and IL-27), while those from children immunized with JBCG did not. In contrast, vaccination with JBCG resulted in significantly greater expression of cytokines characteristic of a proinflammatory immune response (IL-1alpha, IL-1beta, IL-6, and IL-24) in PBMC activated with CFP compared to PBMC from children vaccinated with BBCG or DBCG. Thus, different strains of BCG can activate different immune pathways, which may affect long-term vaccine efficacy.

Microdissection of the cytokine milieu of pulmonary granulomas from tuberculous guinea pigs

Levels of IL-12p40, TNFalpha, TGFbeta, IFNgamma and IL-10 mRNA were assessed by laser capture microdissection followed by quantitative real-time PCR in the pulmonary granulomas of unimmunized and BCG-vaccinated guinea pigs infected by aerosol with virulent Mycobacterium tuberculosis. Lesions microdissected from unimmunized guinea pigs were overwhelmed by the pro-inflammatory TNFalpha mRNA at both 3 and 6 weeks post infection, indicating the struggle to control the mounting infection. The cytokine profile of granulomas from vaccinated guinea pigs shifted from type 1 cytokine mRNA (IFNgamma and IL-12p40) at 3 weeks to a predominantly anti-inflammatory environment (TGFbeta mRNA) at 6 weeks. The relative proportions of cytokine mRNA transcripts in the periphery of the granuloma were different from the centre, reflecting differences in cell composition and architecture. Moreover, analysis of the individual lung lobes at 6 weeks post infection suggests that heterogeneity exists in the cytokine profile between the lobes of the lung.

Development of a guinea pig immune response-related microarray and its use to define the host response following Mycobacterium bovis BCG vaccination

Immune responses in the guinea pig model are understudied because of a lack of commercial reagents. We have developed a custom-made guinea pig oligonucleotide microarray (81 spots) and have examined the gene expression profile of splenocytes restimulated in vitro from Mycobacterium bovis BCG-vaccinated and naive animals. Eleven genes were significantly (P < 0.05) up-regulated following vaccination, indicating a Th1-type response. These results show that microarrays can be used to more fully define immune profiles of guinea pigs.

Production and characterization of guinea pig recombinant gamma interferon and its effect on macrophage activation

Gamma interferon (IFN-gamma) plays a critical role in the protective immune responses against mycobacteria. We previously cloned a cDNA coding for guinea pig IFN-gamma (gpIFN-gamma) and reported that BCG vaccination induced a significant increase in the IFN-gamma mRNA expression in guinea pig cells in response to living mycobacteria and that the virulent H37Rv strain of Mycobacterium tuberculosis stimulated less IFN-gamma mRNA than did the attenuated H37Ra strain. In this study, we successfully expressed and characterized recombinant gpIFN-gamma with a histidine tag at the N terminus (His-tagged rgpIFN-gamma) in Escherichia coli. rgpIFN-gamma was identified as an 18-kDa band in the insoluble fraction; therefore, the protein was purified under denaturing conditions and renatured. N-terminal amino acid sequencing of the recombinant protein yielded the sequence corresponding to the N terminus of His-tagged gpIFN-gamma. The recombinant protein upregulated major histocompatibility complex class II expression in peritoneal macrophages. The antiviral activity of rgpIFN-gamma was demonstrated with a guinea pig fibroblast cell line (104C1) infected with encephalomyocarditis virus. Interestingly, peritoneal macrophages treated with rgpIFN-gamma did not produce any nitric oxide but did produce hydrogen peroxide and suppressed the intracellular growth of mycobacteria. Furthermore, rgpIFN-gamma induced morphological alterations in cultured macrophages. Thus, biologically active rgpIFN-gamma has been successfully produced and characterized in our laboratory. The study of rgpIFN-gamma will further increase our understanding of the cellular and molecular responses induced by BCG vaccination in the guinea pig model of pulmonary tuberculosis.

Lessons from experimental Mycobacterium tuberculosis infections

Mycobacterium tuberculosis is the cause of enormous human morbidity and mortality each year. Although this bacterium can infect and cause disease in many animals, humans are the natural host. For the purposes of studying the pathogenesis of M. tuberculosis, as well as the protective and immunopathologic host responses against this pathogen, suitable animal models must be used. However, modeling the human infection and disease in animals can be difficult, and interpreting the data from animal models must be done carefully. In this paper, the animal models of tuberculosis are discussed, as well as the limitations and advantages of various models. In particular, the lessons we have learned about tuberculosis from the mouse models are highlighted. The careful and thoughtful use of animal models is essential to furthering our understanding of M. tuberculosis, and this knowledge will enhance the discovery of improved treatment and prevention strategies.

Animal models of tuberculosis

It was Robert Koch who recognized the spectrum of pathology of tuberculosis (TB) in different animal species. The examination of clinical specimens from infected humans and animals confirmed the variable patterns of pathological reactions in different species. Guinea pigs are innately susceptible while humans, mice and rabbits show different level of resistance depending upon their genotype. The studies of TB in laboratory animals such as mice, rabbits and guinea pigs have significantly increased our understanding of the aetiology, virulence and pathogenesis of the disease. The introduction of less than five virulent organisms into guinea pigs by the respiratory route can produce lung lesions, bacteraemia and fatal diseases, which helped the extrapolation of results of such experiments to humans. The similarities in the course of clinical infection between guinea pigs and humans allow us to model different forms of TB and to evaluate the protective efficacy of candidate vaccines in such systems. The only limitation of this model, however, is a dearth of immunological reagents that are required for the qualitative and quantitative evaluation of the immune responses, with special reference to cytokines and cell phenotypes. Another limitation is the higher cost of guinea pigs compared with mice. The rabbit is relatively resistant to Mycobacterium tuberculosis, however following infection with virulent Mycobacterium bovis, the rabbit produces pulmonary cavities like humans. The rabbit model, however, is also limited by the lack of the immunological reagents. Mice are the animal of choice for studying the immunology of mycobacterial infections and have contributed much to our current understanding of the roles of various immunological mechanisms of resistance. The resistance of mice to the development of classic TB disease, however, represents a significant disadvantage of the mouse model. Although non-human primates are closely related to humans, owing to high cost and handing difficulties they have not been exploited to a large extent. As all existing animal models fail to mimic the human disease perfectly, efforts should be focused on the development of the non-human primate(s) as the alternative animal model for TB.

Newly designed primer sets available for evaluating various cytokines and iNOS mRNA expression in guinea pig lung tissues by RT-PCR

Guinea pigs are often used as an animal model of human tuberculosis (TB). However, there are few methods available for pursuing the immunological processes involved in guinea pig TB. In this study, we developed for the first time systematic reverse transcription (RT)-PCR for evaluation of guinea pig mRNA expression. RT-PCR primer sets were newly designed for detection of cytokines and inducible nitric oxide synthase (iNOS) mRNA in guinea pig TB. Interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, transforming growth factor (TGF)-beta, interleukin (IL)-1beta, IL-2, IL-10, IL-12p40, granulocyte-macrophage-colony stimulating factor (GM-CSF) and iNOS mRNA expression were detected significantly and reproducibly when these primer sets were used. The data by real-time PCR were comparable with those of RT-PCR. We showed that these RT-PCR primer sets could be used to examine mRNA expression semi-quantitatively in guinea pig tissues, and conclude that these newly designed primer sets for conventional RT-PCR will be useful for studying the immunological processes in guinea pig tuberculosis experiments to investigate and evaluate efficacy of new vaccines or anti-mycobacterial drugs.

Recombinant guinea pig CCL5 (RANTES) differentially modulates cytokine production in alveolar and peritoneal macrophages

The CC chemokine ligand 5 (CCL5; regulated on activation, normal T expressed and secreted) is known to recruit and activate leukocytes; however, its role in altering the responses of host cells to a subsequent encounter with a microbial pathogen has rarely been studied. Recombinant guinea pig (rgp)CCL5 was prepared, and its influence on peritoneal and alveolar macrophage activation was examined by measuring cytokine and chemokine mRNA expression in cells stimulated with rgpCCL5 alone or exposed to rgpCCL5 prior to lipopolysaccharide (LPS) stimulation. Levels of mRNA for guinea pig tumor necrosis factor alpha (TNF-alpha), interleukin (IL)-1beta, CCL2 (monocyte chemoattractant protein-1), and CXC chemokine ligand 8 (IL-8) were analyzed by reverse transcription followed by real-time polymerase chain reaction analysis using SYBR Green. Bioactive TNF-alpha protein concentration was measured using the L929 bioassay. Both macrophage populations displayed significant enhancement of all the genes and TNF-alpha protein levels when stimulated with rgpCCL5, except for CCL2 in alveolar macrophages. When peritoneal or alveolar macrophages were pretreated with rgpCCL5 for 2 h and then exposed to low concentrations of LPS, diminished cytokine and chemokine mRNA levels were apparent at 6 h compared with LPS alone. At the protein level, there was a reduction in TNF-alpha protein at 6 h in the CCL5-pretreated cells compared with LPS alone. These results further support a role for CCL5 in macrophage activation in addition to chemotactic properties and suggest a role in regulating the inflammatory response to LPS in the guinea pig by modulating the production of proinflammatory cytokines by macrophages.

Mycobacterium avium subsp. paratuberculosis infection causes suppression of RANTES, monocyte chemoattractant protein 1, and tumor necrosis factor alpha expression in peripheral blood of experimentally infected cattle

Blood from cattle with subclinical Mycobacterium avium subsp. paratuberculosis infection was stimulated with M. avium subsp. paratuberculosis antigens, and expression of interleukin-1beta (IL-1beta), tumor necrosis factor alpha (TNF-alpha), RANTES, monocyte chemoattractant protein 1 (MCP-1), and IL-8 was measured. Expression of TNF-alpha, RANTES, and MCP-1 was lower in infected than in uninfected cattle. The reduced response may weaken protective immunity and perpetuate infection.

Effect of Mycobacterium bovis BCG vaccination on Mycobacterium-specific cellular proliferation and tumor necrosis factor alpha production from distinct guinea pig leukocyte populations

In this study, we focused on three leukocyte-rich guinea pig cell populations, bronchoalveolar lavage (BAL) cells, resident peritoneal cells (PC), and splenocytes (SPC). BAL cells, SPC, and PC were stimulated either with live attenuated Mycobacterium tuberculosis H37Ra or with live or heat-killed virulent M. tuberculosis H37Rv (multiplicity of infection of 1:100). Each cell population was determined to proliferate in response to heat-killed virulent H37Rv, whereas no measurable proliferative response could be detected upon stimulation with live mycobacteria. Additionally, this proliferative capacity (in SPC and PC populations) was significantly enhanced upon prior vaccination with Mycobacterium bovis BCG. Accordingly, in a parallel set of experiments we found a strong positive correlation between production of antigen-specific bioactive tumor necrosis factor alpha (TNF-alpha) and prior vaccination with BCG. A nonspecific stimulus, lipopolysaccharide, failed to induce this effect on BAL cells, SPC, and PC. These results showed that production of bioactive TNF-alpha from mycobacterium-stimulated guinea pig cell cultures positively correlates with the vaccination status of the host and with the virulence of the mycobacterial strain.

Differential expression of gamma interferon mRNA induced by attenuated and virulent Mycobacterium tuberculosis in guinea pig cells after Mycobacterium bovis BCG vaccination

To determine whether Mycobacterium bovis BCG vaccination would alter gamma interferon (IFN-gamma) mRNA expression in guinea pig cells exposed to Mycobacterium tuberculosis, we cloned a cDNA encoding guinea pig IFN-gamma from a spleen cell cDNA library. The cDNA is composed of 1,110 bp, with an open reading frame encoding a 166-amino-acid protein which shows 56 and 41% amino acid sequence homology to human and mouse IFN-gamma, respectively. Spleen or lymph node cells from naïve and BCG-vaccinated guinea pigs were stimulated with purified protein derivative (PPD) or M. tuberculosis H37Ra or H37Rv, and the total RNA was subjected to Northern blot analysis with a (32)P-labeled probe derived from the cDNA clone. Compared to the IFN-gamma mRNA expression in cells of naïve animals, that in spleen and lymph node cells exposed to various stimuli was enhanced after BCG vaccination. However, there was a significant reduction in IFN-gamma mRNA levels when cells were stimulated with a multiplicity of infection of greater than 1 virulent M. tuberculosis bacterium per 10 cells. The enhanced IFN-gamma mRNA response in BCG-vaccinated animals was associated with an increase in the proportions of CD4(+) T cells in the spleens, as determined by fluorescence-activated cell sorter analysis. Furthermore, the nonadherent population in the spleens enriched either by panning with anti-guinea pig immunoglobulin G-coated plates or by purification on nylon wool columns produced more IFN-gamma mRNA than whole spleen cells following stimulation with concanavalin A or PPD. This indicates that T cells are principally responsible for the upregulation of IFN-gamma mRNA expression following BCG vaccination. The mechanism by which virulent mycobacteria suppress IFN-gamma mRNA accumulation is currently under investigation.

Dynamics of gamma interferon, interleukin-12 (IL-12), IL-10, and transforming growth factor beta mRNA expression in primary Mycobacterium bovis BCG infection in guinea pigs measured by a real-time fluorogenic reverse transcription-PCR assay

The guinea pig has been utilized as a model for studying infectious diseases because its reactions closely resemble those of humans biologically and immunologically. However, the cytokine responses in this animal remain to be studied. Initially, we established a quantitative assay using a real-time reverse transcription-PCR (RT-PCR) to measure guinea pig gamma interferon (IFN-gamma), interleukin-12 (IL-12), IL-10, and transforming growth factor beta (TGF-beta) mRNA. By preparing primer-fluorogenic probe sets for these cytokines and standard RNA templates corresponding to the target sequence of each cytokine, we obtained linear standard curves essential for quantitative determination. In guinea pigs immunized by intradermal (i.d.) vaccination with the Tokyo strain of Mycobacterium bovis BCG (0.1 mg) or else hyperimmunized with the same vaccine (10 mg) given intravenously (i.v.), peripheral blood mononuclear cells (PBMCs) at 4 weeks showed an increase in IFN-gamma mRNA expression in the latter but not the former animals. However, at week 10, IFN-gamma mRNA expression was markedly elevated in PBMCs, spleen cells, and cells in bronchoalveolar lavage fluid in both the i.d.- and the i.v.-immunized animals, the level of expression being 10 times higher in the latter. In contrast, the expression levels of IL-12 mRNA in PBMCs, spleen cells, and BAL cells were not enhanced in either group at 10 weeks postimmunization. The expression of IL-10 and TGF-beta increased slightly only in PBMCs. Regardless of differences in the levels of cytokine responses, the magnitudes of the purified protein derivative of tuberculin-specific delayed-type hypersensitivity (DTH) skin reactions for the two groups did not differ significantly at 8 weeks postvaccination. In this study, we quantitatively measured IL-10, IL-12, TGF-beta, and IFN-gamma mRNA in BCG-immunized guinea pigs and showed that the level of IFN-gamma mRNA expression does not necessarily reflect the magnitude of the DTH response, suggesting that there may be an intricate relationship between protective immunity, the level of IFN-gamma, and the DTH response. Thus, our quantitative assay would be of use for the development of vaccines using guinea pig models.

Mycobacterium bovis BCG vaccination augments interleukin-8 mRNA expression and protein production in guinea pig alveolar macrophages infected with Mycobacterium tuberculosis

Alveolar macrophages are likely the first cell type to encounter Mycobacterium tuberculosis in a pulmonary infection, resulting in the production of chemokines. In order to evaluate this response, alveolar macrophages harvested from nonvaccinated and Mycobacterium bovis BCG-vaccinated guinea pigs were infected in vitro with live M. tuberculosis H37Ra or H37Rv (multiplicity of infection, 1:1) or cultured with lipopolysaccharide (10 micro g/ml) for 3, 12, and 24 h. Interleukin-8 (IL-8) and monocyte chemoattractant protein 1 (MCP-1) mRNA expression was determined by real-time PCR. Culture supernatants were assayed for guinea pig IL-8 protein by using a human IL-8 enzyme-linked immunosorbent assay kit. Alveolar macrophages harvested from BCG-vaccinated guinea pigs produced significantly more mRNA and protein for IL-8 than alveolar macrophages harvested from nonvaccinated guinea pigs at 12 and 24 h poststimulation or postinfection. Infection with attenuated M. tuberculosis (H37Ra) stimulated alveolar macrophages isolated from BCG-vaccinated guinea pigs to produce significantly more IL-8 mRNA than did alveolar macrophages infected with a virulent strain (H37Rv) at 12 and 24 h postinfection. Significant MCP-1 mRNA production was also detected in stimulated or infected alveolar macrophages; however, prior vaccination did not significantly affect levels of MCP-1 mRNA. Alveolar macrophages isolated from BCG-vaccinated guinea pigs produced significantly more IL-8 mRNA and protein when stimulated for 24 h with heat-killed H37Ra, heat-killed H37Rv, and H37Rv cell wall, but not mannose-capped lipoarabinomannan (ManLAM), than did cells stimulated with media alone. These observations indicate that prior vaccination may alter very early events in the M. tuberculosis-infected lung.

5'-adenosinephosphosulfate lies at a metabolic branch point in mycobacteria

Bacterial sulfate assimilation pathways provide for activation of inorganic sulfur for the biosynthesis of cysteine and methionine, through either adenosine 5'-phosphosulfate (APS) or 3'-phosphoadenosine 5'-phosphosulfate (PAPS) as intermediates. PAPS is also the substrate for sulfotransferases that produce sulfolipids, putative virulence factors, in Mycobacterium tuberculosis such as SL-1. In this report, genetic complementation using Escherichia coli mutant strains deficient in APS kinase and PAPS reductase was used to define the M. tuberculosis and Mycobacterium smegmatis CysH enzymes as APS reductases. Consequently, the sulfate assimilation pathway of M. tuberculosis proceeds from sulfate through APS, which is acted on by APS reductase in the first committed step toward cysteine and methionine. Thus, M. tuberculosis most likely produces PAPS for the sole use of this organism's sulfotransferases. Deletion of CysH from M. smegmatis afforded a cysteine and methionine auxotroph consistent with a metabolic branch point centered on APS. In addition, we have redefined the substrate specificity of the B. subtilis CysH, formerly designated a PAPS reductase, as an APS reductase, based on its ability to complement a mutant E. coli strain deficient in APS kinase. Together, these studies show that two conserved sequence motifs, CCXXRKXXPL and SXGCXXCT, found in the C termini of all APS reductases, but not in PAPS reductases, may be used to predict the substrate specificity of these enzymes. A functional domain of the M. tuberculosis CysC protein was cloned and expressed in E. coli, confirming the ability of this organism to make PAPS. The expression of recombinant M. tuberculosis APS kinase provides a means for the discovery of inhibitors of this enzyme and thus of the biosynthesis of SL-1.