Role of CD8 T cells in mycobacterial infections

Tuberculosis vaccine - A timely analysis of the drawbacks for the development of novel vaccines

The BCG vaccine, Bacille Calmette Guerin, holds the distinction of being the most widely administered vaccine. Remarkably, a century has passed since its discovery; however, puzzlingly, questions persist regarding the effectiveness of the immune response it triggers. After years of diligent observation, it has been deduced that BCG imparts immunity primarily to a specific age group, namely children. This prompts a significant query: the rationale behind BCG's limited efficacy against TB in particular age groups and populations remains elusive. Beyond vaccinations, drug therapy has emerged as an alternative route for TB prevention. Nonetheless, this approach faces challenges in the contemporary landscape, marked by the emergence of new instances of MDR-TB and XDR-TB, compounded by the financial burden of treatment. It's noteworthy that BCG remains the sole WHO-approved vaccine for TB. This comprehensive review delves into several aspects, encompassing the immune response during infection, the shortcomings of BCG in conferring immunity, and the various factors contributing to its limitations. Within this discourse, we explore potential explanations for the observed deficiencies of the BCG vaccine and consider how these insights could catalyze the development of future vaccines. The current landscape of novel vaccine development for TB is illuminated, including a spotlight on the latest vaccine candidates.

Ag85b/ESAT6-CFP10 adjuvanted with aluminum/poly-IC effectively protects guinea pigs from latent mycobacterium tuberculosis infection

The high global burden of tuberculosis (TB) underscores the urgent need for an effective TB vaccine since the only licensed Bacillus Calmette-Guérin (BCG) vaccine is ineffective in preventing adult pulmonary TB and affords no protection against latent TB infection (LTBI). Herein we investigated the potential of Mycobacterium tuberculosis (Mtb) antigen proteins AEC comprised of Ag85b and ESAT6-CFP10 proteins in conjunction with aluminum (Al) and polyriboinosinic-polyribocytidylic acid (poly-IC) as a novel subunit vaccine against TB. The immunogenicity and protection induced by the adjuvanted vaccine were evaluated in two animal models. Mice vaccinated with AEC/Al/poly-IC exhibited significant antigen-specific humoral immune responses and cell-mediated immunity as determined by immunoassay and multicolor flow cytometric assay, and the protective effect of the vaccine was demonstrated in a guinea pig model of latent Mtb infection. Compared to the control group, the mean pathological scores and bacterial loads in lungs and spleens of AEC/Al/poly-IC-immunized guinea pigs were significantly reduced. These data indicate that the AEC/Al/poly-IC is highly immunogenic in mice and can effectively protect guinea pigs against latent Mtb infection; it may represent a promising candidate vaccine for the control of latent TB.

Transcriptome Analysis of Bronchoalveolar Lavage Fluid From Children With Mycoplasma pneumoniae Pneumonia Reveals Natural Killer and T Cell-Proliferation Responses

BACKGROUND

Mycoplasma pneumoniae pneumonia (MPP) is one of the most common community-acquired pneumonia; this study is to explore the immune-pathogenesis of children MPP.

METHODS

Next-generation transcriptome sequencing was performed on the bronchoalveolar lavage fluid cells from six children with MPP and three children with foreign body aspiration as control. Some of the results had been validated by quantitative real-time PCR in an expanded group of children.

RESULTS

Results revealed 810 differentially expressed genes in MPP group comparing to control group, of which 412 genes including RLTPR, CARD11 and RASAL3 were upregulated. These upregulated genes were mainly enriched in mononuclear cell proliferation and signaling biological processes. Kyoto encyclopedia of genes and genomes pathway analysis revealed that hematopoietic cell linage pathway, natural killer cell-mediated cytotoxicity pathway, and T cell receptor signaling pathway were significantly upregulated in MPP children. In addition, significant alternative splicing events were found in GNLY and SLC11A1 genes, which may cause the differential expressions of these genes.

CONCLUSION

Our results suggest that NK and CD8+ T cells are over activated and proliferated in MPP children; the upregulated IFNγ, PRF1, GZMB, FASL, and GNLY may play important roles in the pathogenesis of children MPP.

A multi-antigenic MVA vaccine increases efficacy of combination chemotherapy against Mycobacterium tuberculosis

Despite the existence of the prophylactic Bacille Calmette-Guérin (BCG) vaccine, infection by Mycobacterium tuberculosis (Mtb) remains a major public health issue causing up to 1.8 million annual deaths worldwide. Increasing prevalence of Mtb strains resistant to antibiotics represents an urgent threat for global health that has prompted a search for alternative treatment regimens not subject to development of resistance. Immunotherapy constitutes a promising approach to improving current antibiotic treatments through engagement of the host’s immune system. We designed a multi-antigenic and multiphasic vaccine, based on the Modified Vaccinia Ankara (MVA) virus, denoted MVATG18598, which expresses ten antigens classically described as representative of each of different phases of Mtb infection. In vitro analysis coupled with multiple-passage evaluation demonstrated that this vaccine is genetically stable, i.e. fit for manufacturing. Using different mouse strains, we show that MVATG18598 vaccination results in both Th1-associated T-cell responses and cytolytic activity, targeting all 10 vaccine-expressed Mtb antigens. In chronic post-exposure mouse models, MVATG18598 vaccination in combination with an antibiotic regimen decreases the bacterial burden in the lungs of infected mice, compared with chemotherapy alone, and is associated with long-lasting antigen-specific Th1-type T cell and antibody responses. In one model, co-treatment with MVATG18598 prevented relapse of the disease after treatment completion, an important clinical goal. Overall, results demonstrate the capacity of the therapeutic MVATG18598 vaccine to improve efficacy of chemotherapy against TB. These data support further development of this novel immunotherapeutic in the treatment of Mtb infections.

Granzyme B as a diagnostic marker of tuberculosis in patients with and without HIV coinfection

Immunodiagnostic tests for tuberculosis (TB) are based on the estimation of interferon γ (IFN-γ) or IFN-γ-secreting CD4(+) T cells following ex vivo stimulation with ESAT6 and CFP-10. Sensitivity of these tests is likely to be compromised in CD4(+) T-cell-depleted situations, like HIV-TB coinfection. CD4(+) and CD8(+) T cells, isolated from 3 groups, viz., HIV-negative patients with active TB, HIV-TB coinfected patients, and healthy household contacts (HHCs) were cocultivated with autologous dendritic cells, and the cytokine response to rESAT6 stimulation was compared between groups in supernatants. While CD4(+) T-cell stimulation yielded significantly elevated levels of IFN-γ and interleukin 4 in HIV-negative TB patients, compared to HHCs, the levels of both these cytokines were nondiscriminatory between HIV-positive TB patients and HHCs. However, CD8(+) T-cell stimulation yielded significantly elevated granzyme B titers in both groups of patients, irrespective of HIV coinfection status. Hence, contrary to IFN-γ, granzyme B might be a useful diagnostic marker for Mycobacterium tuberculosis infection particularly in HIV coinfected patients.

The beneficial effects of adjunctive recombinant human interleukin-2 for multidrug resistant tuberculosis

INTRODUCTION

Multidrug-resistant tuberculosis (MDR-TB) is a hard-to-treat disease with a poor outcome of chemotherapy. In the present study, the efficacy and safety of recombinant human interleukin-2 (rhIL-2) were investigated in patients with MDR-TB.

MATERIAL AND METHODS

Fifty culture-confirmed patients with MDR-TB were included. Twenty-five patients were randomly assigned to the trial group (injection of 500 000 IU of rhIL-2 once every other day at the first, third, fifth and seventh months in addition to standard multidrug therapy) and another 25 patients to the control group with standard multidrug therapy. All patients were monitored clinically, and T-cell subsets were analyzed by flow cytometry.

RESULTS

The rates of sputum negative conversion and X-ray resolution in the trial group were higher than those of the control, and the improvements were significant by completion of treatment. In addition, CD4(+)CD25(+) T cells in the controls rose gradually during treatment. The levels at the end of the seventh month were significantly higher than before, which were also significantly different when compared with those from the trial group at the same time. However, there were no such changes associated with treatment in the trial group. No significant differences appeared in other T cell subsets.

CONCLUSIONS

Exogenous IL-2 in the present regimen improves immunity status. Adjunctive immunotherapy with a long period of rhIL-2 is a promising treatment modality for MDR-TB.

Combination therapy with α-galactosylceramide and a Toll-like receptor agonist exerts an augmented suppressive effect on lung tumor metastasis in a mouse model

α-galactosylceramide (GalCer), which is a natural killer T (NKT) cell ligand, has been reported to exert therapeutic effects against cancer in humans and mice. Toll-like receptor (TLR) agonists systemically or locally boost antitumor efficacy in mouse cancer models. In our previous study, the co-administration of GalCer and a TLR agonist synergistically enhanced interferon-γ (IFN-γ) production in mouse splenocytes in vitro and in vivo. The increased IFN-γ production promoted a tumor antigen-specific Th1 response. Therefore, co-treatment with GalCer and a TLR agonist is expected to exert an enhanced antitumor effect. In the present study, we examined the effect of GalCer and lipopolysaccharide (LPS) combination therapy in a mouse lung-metastasis model. GalCer and LPS combination therapy markedly decreased the number of lung metastatic tumor nodes. Co-treatment with GalCer and LPS enhanced the mRNA expression of CXCL9 and CXCL10 in mediastinal lymph nodes (MLNs) and increased the number of CD8+ cells in the MLNs. Furthermore, the depletion of CD8+ T cells canceled the antitumor effect of GalCer and LPS combination therapy. Thus, GalCer and LPS combination therapy significantly enhanced tumor antigen-specific immune responses and suppressed tumor growth in a mouse lung-metastasis model.

Shortening the 'short-course' therapy- insights into host immunity may contribute to new treatment strategies for tuberculosis

Achieving global control of tuberculosis (TB) is a great challenge considering the current increase in multidrug resistance and mortality rate. Considerable efforts are therefore being made to develop new effective vaccines, more effective and rapid diagnostic tools as well as new drugs. Shortening the duration of TB treatment with revised regimens and modes of delivery of existing drugs, as well as development of new antimicrobial agents and optimization of the host response with adjuvant immunotherapy could have a profound impact on TB cure rates. Recent data show that chronic worm infection and deficiencies in micronutrients such as vitamin D and arginine are potential areas of intervention to optimize host immunity. Nutritional supplementation to enhance nitric oxide production and vitamin D-mediated effector functions as well as the treatment of worm infection to reduce immunosuppressive effects of regulatory T (Treg) lymphocytes may be more suitable and accessible strategies for highly endemic areas than adjuvant cytokine therapy. In this review, we focus mainly on immune control of human TB, and discuss how current treatment strategies, including immunotherapy and nutritional supplementation, could be optimized to enhance the host response leading to more effective treatment.

Identification of T cell epitopes of Mycobacterium tuberculosis with biolistic DNA vaccination

Tuberculosis (TB) has been listed as one of the most prevalent and serious infectious diseases worldwide. The etiological pathogen of TB is Mycobacterium tuberculosis (Mtb), a facultative intracellular bacterium. Mycobacterium bovis bacillus Calmette-Guérin (BCG) is the only approved vaccine against TB to date. BCG has been widely used, but the efficacy is questionable, especially in adult pulmonary TB. Therefore, more effective, safe and reliable TB vaccines have been urgently needed. T cell-mediated cellular immune response is a key immune response for effective protective immunity against TB. DNA vaccines using Mtb antigens have been studied as promising future TB vaccines. Most TB DNA vaccine studies so far reported used intramuscular or intradermal injection with needles, as these methods tend to induce a type 1 helper T lymphocyte (Th1)-type immune response that is critical for the protective immunity. We have been using DNA vaccines with gene gun bombardment for T cell epitope identification of various Mtb antigens. We show here our strategy to identify precise Mtb T cell epitopes using DNA vaccines with gene gun bombardment.

Identification of murine T-cell epitopes on low-molecular-mass secretory proteins (CFP11, CFP17, and TB18.5) of Mycobacterium tuberculosis

The low-molecular-mass secretory proteins of Mycobacterium tuberculosis have been shown to be major T-cell antigens during infection with the pathogenic bacterium. In this study, we determined murine T-cell epitopes on three low-molecular-mass proteins, CFP11 (Rv2433c), CFP17 (Rv1827), and TB18.5 (Rv0164) using DNA immunization of inbred mice. We analyzed interferon-gamma production from immune splenocytes in response to overlapping peptides covering these proteins. We identified two CD8+ T-cell epitopes on CFP11 and CFP17, one in BALB/c mice and the other in C57BL/6 mice, respectively. On TB18.5, we identified a CD8+ T-cell epitope in BALB/c mice and a CD4+ T-cell epitope in C57BL/6 mice. With the aid of computer algorithms, we could identify the minimal CD8+ T-cell epitopes. These T-cell epitopes are feasible for analysis of the role of antigen-specific T cells during M. tuberculosis infection.

Evaluation of the contribution of major T cell subsets to IFN-gamma production in TB infection by ELISPOT

Interferon gamma remains a key effector molecule that is still widely used as the most informative biomarker for screening human immune responses against tuberculosis, particularly in ELISPOT assays. We investigated the participation of CD4(+) and CD8(+) T lymphocytes in the PBMC responses to Mycobacterium tuberculosis (Mtb) specific antigens in 33 TB cases and 49 contacts. Responses to ESAT-6 were higher than CFP-10. There was no significant difference in responses to both Mtb antigens between cases and contacts. PBMCs response to ESAT-6 but not CFP-10 in cases was significantly reduced by depletion of CD4(+) cells whereas CD8(+) cell depletion had no impact. In conclusion, ESAT-6 is a more recognized antigen in this population, and CD4(+) lymphocytes are the main participants in IFN-gamma response by ELISPOT. Thus, a decline of CD4(+) T lymphocytes below a critical level might affect the sensitivity of IFN-gamma release assays for detecting Mtb infection.

Involvement of CD252 (CD134L) and IL-2 in the expression of cytotoxic proteins in bacterial- or viral-activated human T cells

Regulation of cytotoxic effector molecule expression in human CTLs after viral or bacterial activation is poorly understood. By using human autologous dendritic cells (DCs) to prime T lymphocytes, we found perforin only highly up-regulated in virus- (HSV-1, vaccinia virus) but not in intracellular bacteria- (Listeria innocua, Listeria monocytogenes, Mycobacterium tuberculosis, Chlamydophila pneumoniae) activated CTLs. In contrast, larger quantities of IFN-gamma and TNF-alpha were produced in Listeria-stimulated cultures. Granzyme B and granulysin were similarly up-regulated by all tested viruses and intracellular bacteria. DCs infected with HSV-1 showed enhanced surface expression of the costimulatory molecule CD252 (CD134L) compared with Listeria-infected DC and induced enhanced secretion of IL-2. Adding blocking CD134 or neutralizing IL-2 Abs during T cell activation reduced the HSV-dependent up-regulation of perforin. These data indicate a distinct CTL effector function in response to intracellular pathogens triggered via differing endogenous IL-2 production upon costimulation through CD252.

Identification of an HLA-A*0201-restricted T-cell epitope on the MPT51 protein, a major secreted protein derived from Mycobacterium tuberculosis, by MPT51 overlapping peptide screening

CD8+ T cells play a pivotal role in protection against Mycobacterium tuberculosis infection. We identified a novel HLA-A*0201-restricted CD8+ T-cell epitope on a dominant secreted antigen of M. tuberculosis, MPT51, in HLA-A*0201 transgenic HHD mice. HHD mice were immunized with plasmid DNA encoding MPT51 with gene gun bombardment, and gamma interferon (IFN-gamma) production by the immune splenocytes was analyzed. In response to overlapping synthetic peptides covering the mature MPT51 sequence, the splenocytes were stimulated to produce IFN-gamma by only one peptide, p51-70. Three-color flow cytometric analysis of intracellular IFN-gamma and cell surface CD4 and CD8 staining revealed that the MPT51 p51-70 peptide contains an immunodominant CD8+ T-cell epitope. Further analysis using computer algorithms permitted identification of a bona fide T-cell epitope, p53-62. A major histocompatibility complex class I stabilization assay using T2 cells confirmed that this epitope binds to HLA-A*0201. The T cells were capable of lysing MPT51 p53-62 peptide-pulsed T2 cells. In addition, MPT51 p53-62-specific memory CD8+ T cells were found in tuberculin skin test-positive HLA-A*0201+ healthy individuals. Use of this HLA-A*0201-restricted CD8+ T-cell epitope for analysis of the role of MPT51-specific T cells in M. tuberculosis infection and for design of vaccines against tuberculosis is feasible.

Cutting Edge: Regulatory T cells prevent efficient clearance of Mycobacterium tuberculosis

Mycobacterium tuberculosis remains one of the top microbial killers of humans causing approximately 2 million deaths annually. More than 90% of the 2 billion individuals infected never develop active disease, indicating that the immune system is able to generate mechanisms that control infection. However, the immune response generally fails to achieve sterile clearance of bacilli. Using adoptive cell transfer into C57BL/6J-Rag1(tm1Mom) mice (Rag1(-/-)), we show that regulatory T cells prevent eradication of tubercle bacilli by suppressing an otherwise efficient CD4+ T cell response. This protective CD4+ T cell response was not correlated with increased numbers of IFN-gamma- or TNF-alpha-expressing cells or general expression levels of IFN-gamma or inducible NO synthase in infected organs compared with wild-type C57BL/6 animals. Furthermore, suppression of protection by cotransferred regulatory T cells was neither accompanied by a general increase of IL-10 expression nor by higher numbers of IL-10-producing CD4+ T cells.

Plasma granulysin levels and cellular interferon-gamma production correlate with curative host responses in tuberculosis, while plasma interferon-gamma levels correlate with tuberculosis disease activity in adults

Granulysin is a recently identified cytolytic protein which is expressed by human cytotoxic T-lymphocytes and natural killer (NK)-cells, and has broad antimicrobial and tumoricidal activity. Circulating granulysin levels are associated with T- and NK-cell activity, and may thus reflect protection-associated cellular immune responses. In a case-control study in Indonesia, a highly tuberculosis (TB)-endemic country, we therefore determined plasma granulysin levels in adults with active pulmonary TB before, during, and after TB treatment, both in mild/moderate-TB and advanced-TB patients, and compared these to healthy neighbourhood controls. Adults with active pulmonary TB had significantly lower plasma granulysin levels compared to controls. After 2 months of anti-TB therapy, levels in TB patients had significantly increased, reaching values similar to those in controls. Plasma granulysin levels further increased after completion of TB therapy, being significantly higher than those in controls. Plasma granulysin levels correlated inversely with TB disease activity but not with TB disease severity. In contrast, plasma interferon-gamma (IFN-gamma) levels were significantly higher in active TB cases than in controls, normalised during treatment and correlated with both TB disease activity and TB disease severity. At the cellular level, granulysin and IFN-gamma expression both correlated inversely with disease activity. Interestingly, granulysin was predominantly expressed by IFN-gamma negative T-cells, suggesting that the cellular sources of IFN-gamma and granulysin in TB are partly non-overlapping. The observation that plasma granulysin levels and cellular IFN-gamma production correlate with curative host responses in pulmonary tuberculosis points to a potentially important role of granulysin, next to IFN-gamma, in host defence against M. tuberculosis.

Gamma interferon responses of CD4 and CD8 T-cell subsets are quantitatively different and independent of each other during pulmonary Mycobacterium bovis BCG infection

Gamma interferon (IFN-gamma) is a key cytokine in host defense against intracellular mycobacterial infection. It has been believed that both CD4 and CD8 T cells are the primary sources of IFN-gamma. However, the relative contributions of CD4 and CD8 T-cell subsets to IFN-gamma production and the relationship between CD4 and CD8 T-cell activation have not been examined. By using a model of pulmonary mycobacterial infection and various immunodetection assays, we found that CD4 T cells mounted a much stronger IFN-gamma response than CD8 T cells at various times after mycobacterial infection, and this pronounced IFN-gamma production by CD4 T cells was attributed to both greater numbers of antigen-specific CD4 T cells and a greater IFN-gamma secretion capacity of these cells. By using major histocompatibility complex class II-deficient or CD4-deficient mice, we found that the lack of CD4 T cells did not negatively affect primary or secondary CD8 T-cell IFN-gamma responses. The CD8 T cells activated in the absence of CD4 T cells were capable of immune protection against secondary mycobacterial challenge. Our results suggest that, whereas both CD4 and CD8 T cells are capable of IFN-gamma production, the former represent a much greater cellular source of IFN-gamma. Moreover, during mycobacterial infection, CD8 T-cell IFN-gamma responses and activation are independent of CD4 T-cell activation.

Analysis of IL1B, TAP1, TAP2 and IKBL polymorphisms on susceptibility to tuberculosis

Genetic determinants of human susceptibility to tuberculosis (TB) have not been completely elucidated. Interleukin-1 beta (IL-1beta) and the inhibitor of kB-like (IkBL) are important molecules that participate in the inflammatory response required for the immunological control of a broad spectrum of infectious agents. The transporter associated with antigen processing (TAP) is involved in the antigen processing via major histocompatibility complex class I molecules and in turn might regulate the T-cell response against Mycobacterium tuberculosis. To better characterize the host genetic factors determining the susceptibility to TB, we evaluated the influence of functional polymorphisms in IL1B, TAP and IKBL genes on the risk of developing pulmonary TB in a Northwestern Colombian population, an endemic area of M. tuberculosis infection. A total of 122 TB patients and 166 healthy controls (N = 166) negative for human immunodeficiency virus infection were examined for IL1B-511 and +3,953, TAP1 and TAP2 and IKBL+738 polymorphisms. Univariate analysis disclosed significant differences between patients and controls for IL1B+3,953 polymorphism. After unconditional logistic regression analysis, a strong protection conferred by IL1B+3,953 T-allele-carrying genotypes was observed. A trend between TAP2*0201 allele and disease was observed. Association between IL1B-511, TAP1 or IKBL polymorphisms and TB disease was not found. These results indicate that a functional polymorphism in the IL1B gene influences the susceptibility to TB and suggest a role for IL-1beta in the pathogenesis of mycobacterial infection.

Contribution of CD8+T Cells to Control ofMycobacterium tuberculosisInfection

Tuberculosis is the number one cause of death due to infectious disease in the world today. Understanding the dynamics of the immune response is crucial to elaborating differences between individuals who contain infection vs those who suffer active disease. Key cells in an adaptive immune response to intracellular pathogens include CD8(+) T cells. Once stimulated, these cells provide a number of different effector functions, each aimed at clearing or containing the pathogen. To explore the role of CD8(+) T cells in an integrative way, we synthesize both published and unpublished data to build and test a mathematical model of the immune response to Mycobacterium tuberculosis in the lung. The model is then used to perform a series of simulations mimicking experimental situations. Selective deletion of CD8(+) T cell subsets suggests a differential contribution for CD8(+) T cell effectors that are cytotoxic as compared with those that produce IFN-gamma. We also determined the minimum levels of effector memory cells of each T cell subset (CD4(+) and CD8(+)) in providing effective protection following vaccination.

Characterization of the immunological features of tuberculous pericardial effusions in HIV positive and HIV negative patients in contrast with non-tuberculous effusions

OBJECTIVE

To investigate the immunopathogenesis of pericardial tuberculosis (TB) and the influence of human immunodeficiency virus (HIV) on the anti-tuberculous immune response.

DESIGN

Consecutive patients presenting with large pericardial effusions were subjected to a full clinical examination and pericardiocentesis. Aspirated fluid was sent for biochemistry, differential leukocyte count, flow cytometric analysis and determination of cytokine levels. Pericardial tissue was sent for TB culture and histopathological evaluation. Diagnoses were made according to pre-determined criteria.

RESULTS

Fifty-six patients were included and divided into HIV positive TB (n = 22), HIV negative TB (n = 21) and non-tuberculous effusions (n = 13). Peripheral blood neutrophil, lymphocyte and monocyte counts were significantly lower in HIV positive TB patients. Lymphocytes were the dominant cell type in tuberculous pericardial effusions. CD4+ cells dominated in HIV negative tuberculous effusions, whereas CD8+ cells dominated in HIV positive TB. The difference in the concentration of IFN-gamma levels in the tuberculous and non-tuberculous pericardial effusions was statistically significant. Despite significant differences in pericardial CD4+ cell counts, IFN-gamma levels were similarly elevated in HIV negative and HIV positive tuberculous effusions. Highest levels of pericardial IL-10 were observed in samples associated with least tissue necrosis, suggesting the possibility of a tissue protective immunoregulatory role for IL-10.

CONCLUSIONS

Tuberculous pericardial effusions result from a T helper1 (Th1)-dominant immune response. IFN-gamma producing CD4+ lymphocytes dominate in HIV negative patients, whereas CD8+ seem to play a more important role in HIV positive patients. Infection with HIV leads to the depletion of immunocompetent cells such as monocytes, NK cells and neutrophils.

Rhodococcus equi-specific cytotoxic T lymphocytes in immune horses and development in asymptomatic foals

Rhodococcus equi is an important cause of pneumonia in young horses; however, adult horses are immune due to their ability to mount protective recall responses. In this study, the hypothesis that R. equi-specific cytotoxic T lymphocytes (CTL) are present in the lung of immune horses was tested. Bronchoalveolar lavage (BAL)-derived pulmonary T lymphocytes stimulated with R. equi lysed infected alveolar macrophages and peripheral blood adherent cells (PBAC). As with CTL obtained from the blood, killing of R. equi-infected targets by pulmonary effectors was not restricted by equine lymphocyte alloantigen-A (ELA-A; classical major histocompatibility complex class I), suggesting a novel or nonclassical method of antigen presentation. To determine whether or not CTL activity coincided with the age-associated susceptibility to rhodococcal pneumonia, CTL were evaluated in foals. R. equi-stimulated peripheral blood mononuclear cells (PBMC) from 3-week-old foals were unable to lyse either autologous perinatal or mismatched adult PBAC targets. The defect was not with the perinatal targets, as adult CTL effectors efficiently killed infected targets from 3-week-old foals. In contrast, significant CTL activity was present in three of five foals at 6 weeks of age, and significant specific lysis was induced by PBMC from all foals at 8 weeks of age. As with adults, lysis was ELA-A unrestricted. Two previously described monoclonal antibodies, BCD1b3 and CD1F2/1B12.1, were used to examine the expression of CD1, a nonclassical antigen-presenting molecule, on CTL targets. These antibodies cross-reacted with both foal and adult PBAC. However, neither antibody bound alveolar macrophages, suggesting that the R. equi-specific, major histocompatibility complex-unrestricted lysis is not restricted by a surface molecule identified by these antibodies.

Cytolytic CD8+ T cells recognizing CFP10 are recruited to the lung after Mycobacterium tuberculosis infection

Optimum immunity against Mycobacterium tuberculosis requires both CD4⁺ and CD8⁺ T cells. In contrast with CD4⁺ T cells, few antigens are known that elicit CD8⁺ T cells during infection. CD8⁺ T cells specific for culture filtrate protein-10 (CFP10) are found in purified protein derivative positive donors, suggesting that CFP10 primes CD8⁺ T cells in vivo. Using T cells from M. tuberculosis–infected mice, we identified CFP10 epitopes recognized by CD8⁺ T cells and CD4⁺ T cells. CFP10-specific T cells were detected as early as week 3 after infection and at their peak accounted for up to 30% of CD8⁺ T cells in the lung. IFNγ-producing CD8⁺ and CD4⁺ T cells recognizing CFP10 epitopes were preferentially recruited to the lungs of M. tuberculosis–infected mice. In vivo cytolytic activity of CD8⁺ T cells specific for CFP10 and TB10.3/10.4 proteins was detected in the spleen, pulmonary lymph nodes, and lungs of infected mice. The cytolytic activity persisted long term and could be detected 260 d after infection. This paper highlights the cytolytic function of antigen-specific CD8⁺ T cells elicited by M. tuberculosis infection and demonstrates that large numbers of CFP10-specific cytolytic CD8⁺ T cells are recruited to the lung after M. tuberculosis infection.

Mycobacterial granulomas: keys to a long-lasting host-pathogen relationship

Chronic infection with mycobacteria is controlled by the formation of granulomas. The failure of granuloma maintenance results in reactivation of disease. Macrophages are the dominant cell type in granulomas, but CD4+ T cells are the master organizers of granuloma structure and function. Recent work points to an unrecognized role for nonspecific T cells in maintaining granuloma function in the chronic phase of infection. In addition, it has become clear that mycobacteria and host T cells collaborate in formation of granulomas. Further understanding of how nonspecific T cells contribute to granuloma formation, as well as how bacteria and T cells maintain a harmonious relationship over the life of the host, will facilitate the development of new strategies to treat mycobacterial disease.

Investigation of the role of CD8+ T cells in bovine tuberculosis in vivo

Mycobacterium bovis is the causative agent of bovine tuberculosis (TB), and it has the potential to induce disease in humans. CD8(+) T cells (CD8 cells) have been shown to respond to mycobacterial antigens in humans, cattle, and mice. In mice, CD8 cells have been shown to play a role in protection against mycobacterial infection. To determine the role of CD8 cells in bovine TB in vivo, two groups of calves were infected with the virulent M. bovis strain AF2122/97. After infection, one group was injected with a CD8 cell-depleting monoclonal antibody (MAb), and the other group was injected with an isotype control MAb. Immune responses to mycobacterial antigens were measured weekly in vitro. After 8 weeks, the animals were killed, and postmortem examinations were carried out. In vitro proliferation responses were similar in both calf groups, but in vitro gamma interferon (IFN-gamma) production in 24-h whole-blood cultures was significantly higher in control cattle than in CD8 cell-depleted calves. Postmortem examination showed that calves in both groups had developed comparable TB lesions in the lower respiratory tract and associated lymph nodes. Head lymph node lesion scores, on the other hand, were higher in control calves than in CD8 cell-depleted calves. Furthermore, there was significant correlation between the level of IFN-gamma and the head lymph node lesion score. These experiments indicate that CD8 cells play a role in the immune response to M. bovis in cattle by contributing to the IFN-gamma response. However, CD8 cells may also play a deleterious role by contributing to the immunopathology of bovine TB.

Mice lacking the multidrug resistance protein 1 have a transiently impaired immune response during tuberculosis

A T helper (Th) 1 immune response is important for host defense against tuberculosis. The multidrug resistance protein (Mrp) 1 is constitutively present at low levels on Th2 lymphocytes, and is expressed on Th1 lymphocytes upon activation. To determine the role of Mrp1 in the pathogenesis of tuberculosis, Mrp1 deficient (-/-) and normal wild type mice were intranasally infected with Mycobacterium tuberculosis. At 2 weeks after infection, Mrp1(-/-) mice had reduced levels of the Th1 cytokine interferon-gamma and an impaired granuloma formation in their lungs. At 5 weeks postinfection, M. tuberculosis outgrowth was enhanced in lungs and livers of Mrp1(-/-) mice. A more prolonged observation of these mice, up to 4 months, revealed no differences in survival or mycobacterial outgrowth. These data suggest that Mrp1 plays an early but dispensable role in the protective immune response to pulmonary tuberculosis.

Antigen-specific activation and proliferation of CD4+ and CD8+ T lymphocytes from brucellosis patients

Salt-extractable antigen from Brucella melitensis 16M (RCM-BM) was used to evaluate the immune response from acute and chronic patients suffering from Brucella infections (in Mexico); their responses were compared with those of healthy controls. As a readout we used upregulation of CD69 (a well-established early activation marker for lymphocytes), lymphocyte proliferation by 3[H]thymidine or 5-bromo-2-deoxyuridine (BrdU) incorporation measured by liquid scintillation or flow cytometry, respectively, and production of gamma interferon (IFN gamma). We compared the antigen-specific response with the response induced by phytohaemagglutinin (PHA) as a positive control. There was no difference between acute patients and the healthy controls in the percentages of CD3+, CD4+ or CD8+ lymphocytes. However, we found that chronic patients had a significant (P < 0.05) increase in the CD8+ T cells, in line with previous studies. Antigen-specific responses to RCM-BM showed a significant (P < 0.05) upregulation of CD69 in both CD4+ and CD8+ T lymphocytes in acute brucellosis patients and in CD8+ T lymphocytes in chronic patients, indicating that both populations became activated by this antigen preparation. Moreover, lymphocyte proliferation from both acute and chronic patients in response to RCM-BM was highly significant (P < 0.001) when compared with healthy controls. However, there were no apparent differences between acute and chronic patients. Although the incorporation of BrdU showed similar results it provided additional information, since we demonstrated that both CD4+ and CD8+ T lymphocytes from acute and chronic patients proliferated equally well in response to RCM-BM. Similar results were observed with intracellular IFN gamma determination. As a whole, our data suggest an important role for both CD4+ and CD8+ T lymphocytes in Brucella infection in humans. As has been reported in mice, it is feasible that activated CD8+ T cells participate in protection against Brucella in humans through cytotoxicity or/and by the production of factors such as interferon and granulysin. The role of these cells should be carefully analysed to understand better their participation in human infection by Brucella.

HLA-B*35-restricted CD8(+)-T-cell epitope in Mycobacterium tuberculosis Rv2903c

Few human CD8(+) T-cell epitopes in mycobacterial antigens have been described to date. Here we have identified a novel HLA-B*35-restricted CD8(+) T-cell epitope in Mycobacterium tuberculosis Rv2903c based on a reverse immunogenetics approach. Peptide-specific CD8 T cells were able to kill M. tuberculosis-infected macrophages and produce gamma interferon and tumor necrosis factor alpha.

MHC class Ia-restricted T cells partially account for beta2-microglobulin-dependent resistance to Mycobacterium tuberculosis

Recent studies have highlighted the heterogeneous nature of the CD8(+) T cell response during human Mycobacterium tuberculosis infection; MHC class Ia, MHC class Ib and CD1 have all been identified as significant restriction elements. Here we have attempted to define the role of MHC class Ia in resistance to M. tuberculosis infection in mice. The course of M. tuberculosis infection in mice deficient in a single MHC class Ia molecule, either H2-K(b) or H2-D(b), was essentially identical to that observed in wild-type mice. In contrast, mice fully deficient in MHC class Ia molecules (H2-K(b) / H2-D(b) double knockout mice) were substantially more susceptible to M. tuberculosis infection. However, the double knockout mice were not as susceptible as beta 2-microglobulin-deficient mice, which have a broader phenotypic deficit. Thus, antigen presentation via MHC class Ia is an important component in resistance to M. tuberculosis, but its absence only partially accounts for the increased susceptibility of beta 2-microglobulin-deficient mice.

Extensive Mycobacterium bovis BCG infection of liver parenchymal cells in immunocompromised mice

A histologic study was performed on the livers of wild-type (WT), severe combined immunodeficient (SCID), hydrocortisone acetate (HC)-treated WT, and HC-treated SCID mice infected intravenously with 10(5) CFU of Mycobacterium bovis BCG. It was found that infection progressed faster in SCID mice than in WT mice and that HC treatment caused exacerbation of infection in both types of mice. In all cases infection in the liver was confined to granulomas that were populated predominantly by macrophages. Higher levels of infection in HC-treated SCID mice, but not HC-treated WT mice, were associated with extensive infection and destruction of parenchymal cells at the margins of granulomas. The results indicate that in the absence of T-cell-mediated immunity and of HC-sensitive T-cell-independent defense mechanisms, macrophages are incapable of restricting BCG growth and of confining infection to their cytoplasm. Consequently, BCG bacilli are released into the extracellular environment, where they are ingested by neighboring parenchymal cells.

Recent advances in our understanding of human host responses to tuberculosis

Tuberculosis remains one of the world's greatest public health challenges: 2 billion persons have latent infection, 8 million people develop active tuberculosis annually, and 2-3 million die. Recently, significant advances in our understanding of the human immune response against tuberculosis have occurred. The present review focuses on recent work in macrophage and T-cell biology that sheds light on the human immune response to tuberculosis. The role of key cytokines such as interferon-gamma is discussed, as is the role of CD4+ and CD8+ T cells in immune regulation in tuberculosis, particularly with regard to implications for vaccine development and evaluation.

Vaccinia expression of Mycobacterium tuberculosis-secreted proteins: tissue plasminogen activator signal sequence enhances expression and immunogenicity of M. tuberculosis Ag85

There is increasing evidence to implicate a role for CD8(+) T cells in protective immunity against tuberculosis. Recombinant vaccinia (rVV) expressing Mycobacterium tuberculosis (MTB) proteins can be used both as tools to dissect CD8(+) T-cell responses and, in attenuated form, as candidate vaccines capable of inducing a balanced CD4(+)/CD8(+) T-cell response. A panel of rVV was constructed to express four immunodominant secreted proteins of MTB: 85A, 85B and 85C and ESAT-6. A parallel group of rVV was constructed to include the heterologous eukaryotic tissue plasminogen activator (tPA) signal sequence to assess if this would enhance expression and immunogenicity. Clear expression was obtained for 85A, 85B and ESAT-6 and the addition of tPA resulted in N-glycosylation and a 4-10-fold increase in expression. Female C57BL/6 mice were immunised using the rVV-Ag85 constructs, and interleukin-2 and gamma-interferon were assayed using a co-culture of immune splenocytes and recall antigen. There was a marked increase in cytokine production in mice immunised with the tPA-containing constructs. We report the first data demonstrating enhanced immunogenicity of rVV using a tPA signal sequence, which has significant implications for future vaccine design.