Dichotomy of cytokine profiles in patients and high-risk healthy subjects exposed to tuberculosis

Th2 immune response by the iron-regulated protein HupB of Mycobacterium tuberculosis

BACKGROUND

HupB is an iron-regulated protein essential for the growth of Mycobacterium tuberculosis inside macrophages. To investigate if HupB induced a dominant Th2 type immune response, we studied the effect of rHupB on PBMCs from TB patients and by infecting mouse macrophages with wild type and hupB KO mutants.

METHODS

PBMCs from pulmonary TB (n = 60), extra pulmonary TB (n = 23) and healthy controls (n = 30) were stimulated with purified HupB and the cytokines secreted were assayed. The sera were screened for anti-HupB antibodies by ELISA. Mouse macrophages cell line (RAW 264.7) was infected with wild type, hupB KO and hupB-complemented strains of M. tuberculosis grown in high and low iron medium and the expression of cytokines was assayed by qRT-PCR.

RESULTS

Murine macrophages infected with the hupB KO strain produced low levels of the pro-inflammatory cytokines IFN-γ, TNF-α, IL-1, and IL-18 and high levels of IL-10. HupB induced IL-6 and IL-10 production in PBMCs of TB patients and down-regulated IFN-γ and TNF-α production. The influence of HupB was remarkable in the EPTB group.

CONCLUSION

HupB shifted the immune response to the Th2 type. Low IFN-γ and elevated IL-10 in EPTB patients is noteworthy.

Prevalence of toxoplasmosis in patients infected with tuberculosis; a sero-molecular case-control study in northwest Iran

In this study, we investigated the possible association between TB and Toxoplasma gondii infection. One hundred confirmed TB individuals living in northwest Iran were classified into three subgroups; newly diagnosed patients (NTB), old diagnosed patients (OTB) and multidrug resistance patients (MDR-TB). One hundred healthy subjects in the same age and sex distribution were ethnically matched. Sera samples were screened for anti-Toxoplasma antibodies. Nested-PCR was performed by targeting the B1 and GRA6 genes. The frequency of Toxoplasma infection based on IgG titer was 71.1% in the OTB subgroup and 33% in the control group, indicating significant association between Toxoplasma seropositivity and OTB (P = 0.001). According to phylogenetic network, the type I strain of Toxoplasma was identified in the OTB subgroup (10.1%). We concluded that patients with OTB subgroup are at high risk for acquisition of Toxoplasma infection which could reactivate the latent toxoplasmosis.

Immunology of Mycobacterium tuberculosis Infections

Tuberculosis (TB) is a serious global public health challenge that results in significant morbidity and mortality worldwide. TB is caused by infection with the bacilli Mycobacterium tuberculosis (M. tuberculosis), which has evolved a wide variety of strategies in order to thrive within its host. Understanding the complex interactions between M. tuberculosis and host immunity can inform the rational design of better TB vaccines and therapeutics. This chapter covers innate and adaptive immunity against M. tuberculosis infection, including insights on bacterial immune evasion and subversion garnered from animal models of infection and human studies. In addition, this chapter discusses the immunology of the TB granuloma, TB diagnostics, and TB comorbidities. Finally, this chapter provides a broad overview of the current TB vaccine pipeline.

Single-Cell Cytokine Gene Expression in Peripheral Blood Cells Correlates with Latent Tuberculosis Status

RNA flow cytometry (FISH-Flow) achieves high-throughput measurement of single-cell gene expression by combining in-situ nucleic acid hybridization with flow cytometry. We tested whether antigen-specific T-cell responses detected by FISH-Flow correlated with latent tuberculosis infection (LTBI), a condition affecting one-third of the world population. Peripheral-blood mononuclear cells from donors, identified as positive or negative for LTBI by current medical practice, were stimulated ex vivo with mycobacterial antigen. IFNG and IL2 mRNA production was assayed by FISH-Flow. Concurrently, immunophenotypes of the cytokine mRNA-positive cells were characterized by conventional, antibody-based staining of cell-surface markers. An association was found between donor LTBI status and antigen-specific induction of IFNG and IL2 transcripts. Induction of these cytokine genes, which was detected by FISH-Flow in a quarter the time required to see release of the corresponding proteins by ELISA, occurred primarily in activated CD4+ T cells via T-cell receptor engagement. Moreover, NK cells contributed to IFNG gene induction. These results show that antigen-driven induction of T-cell cytokine mRNA is a measurable single-cell parameter of the host responses associated with latent tuberculosis. FISH-Flow read-outs contribute a multi-scale dimension to the immunophenotyping afforded by antibody-based flow cytometry. Multi-scale, single-cell analyses may satisfy the need to determine disease stage and therapy response for tuberculosis and other infectious pathologies.

Complexity and Controversies over the Cytokine Profiles of T Helper Cell Subpopulations in Tuberculosis

Tuberculosis (TB) is a contagious infectious disease caused by the TB-causing bacillus Mycobacterium tuberculosis and is considered a public health problem with enormous social impact. Disease progression is determined mainly by the balance between the microorganism and the host defense systems. Although the immune system controls the infection, this control does not necessarily lead to sterilization. Over recent decades, the patterns of CD4+ T cell responses have been studied with a goal of complete understanding of the immunological mechanisms involved in the maintenance of latent or active tuberculosis infection and of the clinical cure after treatment. Conflicting results have been suggested over the years, particularly in studies comparing experimental models and human disease. In recent years, in addition to Th1, Th2, and Th17 profiles, new standards of cellular immune responses, such as Th9, Th22, and IFN-γ-IL-10 double-producing Th cells, discussed here, have also been described. Additionally, many new roles and cellular sources have been described for IL-10, demonstrating a critical role for this cytokine as regulatory, rather than merely pathogenic cytokine, involved in the establishment of chronic latent infection, in the clinical cure after treatment and in keeping antibacillary effector mechanisms active to prevent immune-mediated damage.

Expression pattern of transcription factors and intracellular cytokines reveals that clinically cured tuberculosis is accompanied by an increase in Mycobacterium-specific Th1, Th2, and Th17 cells

Tuberculosis (TB) remains a major global health problem and is the second biggest cause of death by infectious disease worldwide. Here, we investigate in vitro the Th1, Th2, Th17, and Treg cytokines and transcriptional factors produced after Mycobacterium-specific antigen stimulation in patients with active pulmonary tuberculosis, clinically cured pulmonary tuberculosis, and healthy donors with a positive tuberculin skin test (TST+). Together, our data indicate that clinical cure after treatment increases the percentages of Mycobacterium-specific Th1, Th2, and Th17 cells compared with those found in active-TB and TST+ healthy donors. These results show that the host-parasite equilibrium in latent TB breaks in favor of the microorganism and that the subsequent clinical recovery posttreatment does not return the percentage levels of such cells to those observed in latent tuberculosis. Additionally, our results indicate that rather than showing an increase in the percentage of Mycobacterium-specific Tregs, active-TB patients display lower Th1 : Treg and Th17 : Treg ratios. These data, together with lower Th1 : Th2 and Th17 : Th2 ratios, may indicate a mechanism by which the breakdown of the host-parasite equilibrium leads to active-TB and changes in the repertoire of Mycobacterium-specific Th cells that are associated with clinical cure after treatment of pulmonary tuberculosis.

Simultaneous inhibition of T helper 2 and T regulatory cell differentiation by small molecules enhances Bacillus Calmette-Guerin vaccine efficacy against tuberculosis

Tuberculosis affects nine million individuals and kills almost two million people every year. The only vaccine available, Bacillus Calmette-Guerin (BCG), has been used since its inception in 1921. Although BCG induces host-protective T helper 1 (Th1) cell immune responses, which play a central role in host protection, its efficacy is unsatisfactory, suggesting that additional methods to enhance protective immune responses are needed. Recently we have shown that simultaneous inhibition of Th2 cells and Tregs by using the pharmacological inhibitors suplatast tosylate and D4476, respectively, dramatically enhances Mycobacterium tuberculosis clearance and induces superior Th1 responses. Here we show that treatment with these two drugs during BCG vaccination dramatically improves vaccine efficacy. Furthermore, we demonstrate that these drugs induce a shift in the development of T cell memory, favoring central memory T (Tcm) cell responses over effector memory T (Tem) cell responses. Collectively, our findings provide evidence that simultaneous inhibition of Th2 cells and Tregs during BCG vaccination promotes vaccine efficacy.

Pulmonary tuberculosis in Asian elephants (Elephas maximus): histologic lesions with correlation to local immune responses

Although Mycobacterium tuberculosis infection is an important health concern for Asian elephants (Elephas maximus), no studies have evaluated the associated local immune responses or histologic lesions. In primates including humans, latent tuberculosis is distinguished by well-organized granulomas with TH1 cytokine expression, whereas active disease is characterized by poorly organized inflammation and local imbalance in TH1/TH2 cytokines. This study examined archival, formalin-fixed, paraffin-embedded lung samples from 5 tuberculosis-negative and 9 tuberculosis-positive Asian elephants. Lesions were assessed by light microscopy, and lymphoid infiltrates were characterized by CD3 and CD20 immunolabeling. Expression of TH1 (interferon [IFN]-γ, tumor necrosis factor [TNF]-α) and TH2 (interleukin [IL]-4, IL-10, transforming growth factor [TGF]-β) cytokines was determined using in situ hybridization. In 6 of 9 samples, inflammation was similar to the pattern of primate active disease with low to moderate numbers of lymphocytes, most of which were CD20 positive. In 1 sample, inflammation was most similar to latent tuberculosis in primates with numerous CD3-positive lymphocytes. Expression of IFN-γ was detected in 3 of 8 tuberculosis-positive samples. Expression of TNF-α was detected in 3 of 8 positive samples, including the one with latent morphology. Low-level expression of IL-4 was present in 4 of 8 positive samples. Only single positive samples displayed expression of IL-10 and TGF-β. Tuberculosis-negative samples generally lacked cytokine expression. Results showed heterogeneity in lesions of elephant tuberculosis similar to those of latent and active disease in primates, with variable expression of both TH1 and TH2 cytokines.

The IL-13/IL-4Rα axis is involved in tuberculosis-associated pathology

Human tuberculosis (TB) is a leading global health threat and still constitutes a major medical challenge. However, mechanisms governing tissue pathology during post-primary TB remain elusive, partly because genetically or immunologically tractable animal models are lacking. In human TB, the demonstration of a large relative increase in interleukin (IL)-4 and IL-13 expression, which correlates with lung damage, indicates that a subversive T helper (TH)2 component in the response to Mycobacterium tuberculosis (Mtb) may undermine protective immunity and contribute to reactivation and tissue pathology. Up to now, there has been no clear evidence regarding whether IL-4/IL-13-IL-4 receptor-α (Rα)-mediated mechanisms may in fact cause reactivation and pathology. Unfortunately, the virtual absence of centrally necrotizing granulomas in experimental murine TB is associated with a poor induction of a TH2 immune response. We therefore hypothesize that, in mice, an increased production of IL-13 may lead to a pathology similar to human post-primary TB. In our study, aerosol Mtb infection of IL-13-over-expressing mice in fact resulted in pulmonary centrally necrotizing granulomas with multinucleated giant cells, a hypoxic rim and a perinecrotic collagen capsule, with an adjacent zone of lipid-rich, acid-fast bacilli-containing foamy macrophages, thus strongly resembling the pathology in human post-primary TB. Granuloma necrosis (GN) in Mtb-infected IL-13-over-expressing mice was associated with the induction of arginase-1-expressing macrophages. Indirect blockade of the endogenous arginase inhibitor l-hydroxyarginine in Mtb-infected wild-type mice resulted in a strong arginase expression and precipitated a similar pathology of GN. Together, we here introduce an experimental TB model that displays many features of centrally necrotizing granulomas in human post-primary TB and demonstrate that IL-13/IL-4Rα-dependent mechanisms leading to arginase-1 expression are involved in TB-associated tissue pathology.

Differences in immune cell function between tuberculosis positive and negative Asian elephants

Tuberculosis is an important health concern for Asian elephant (Elephas maximus) populations worldwide, however, mechanisms underlying susceptibility to Mycobacterium tuberculosis are unknown. Proliferative responses assessed via brominated uridine incorporation and cytokine expression measured by real-time RT-PCR were evaluated in peripheral blood mononuclear cell (PBMC) cultures from 8 tuberculosis negative and 8 positive Asian elephants. Cultures were stimulated with Mycobacterium bovis purified protein derivative (PPD-B), M. tuberculosis culture filtrate protein (CFP)-10, and Mycobacterium avium PPD (PPD-A). Following stimulation with PPD-B, proliferation was higher (α = 0.005) in positive samples; no significant differences were detected following CFP-10 or PPD-A stimulation. Tumor necrosis factor (TNF)-α, interleukin (IL)-12, and interferon (IFN)-γ expression was greater in samples from positive elephants following stimulation with PPD-B (α = 0.025) and CFP-10 (α = 0.025 TNF-α and IL-12; α = 0.005 IFN-γ). Stimulation with PPD-A also produced enhanced IL-12 expression in positive samples (α = 0.025). Findings suggested that differences in immune cell function exist between tuberculosis positive and negative elephants. Proliferative responses and expression of TNF-α, IL-12, and IFN-γ in response to stimulation with PPD-B and CFP-10 differ between tuberculosis positive and negative elephants, suggesting these parameters may be important to tuberculosis immunopathogenesis in this species.

iNKT cell production of GM-CSF controls Mycobacterium tuberculosis

Invariant natural killer T (iNKT) cells are activated during infection, but how they limit microbial growth is unknown in most cases. We investigated how iNKT cells suppress intracellular Mycobacterium tuberculosis (Mtb) replication. When co-cultured with infected macrophages, iNKT cell activation, as measured by CD25 upregulation and IFNγ production, was primarily driven by IL-12 and IL-18. In contrast, iNKT cell control of Mtb growth was CD1d-dependent, and did not require IL-12, IL-18, or IFNγ. This demonstrated that conventional activation markers did not correlate with iNKT cell effector function during Mtb infection. iNKT cell control of Mtb replication was also independent of TNF and cell-mediated cytotoxicity. By dissociating cytokine-driven activation and CD1d-restricted effector function, we uncovered a novel mediator of iNKT cell antimicrobial activity: GM-CSF. iNKT cells produced GM-CSF in vitro and in vivo in a CD1d-dependent manner during Mtb infection, and GM-CSF was both necessary and sufficient to control Mtb growth. Here, we have identified GM-CSF production as a novel iNKT cell antimicrobial effector function and uncovered a potential role for GM-CSF in T cell immunity against Mtb.

Mycobacterium tuberculosis (Mtb) is the cause of tuberculosis, a leading cause of sickness and death worldwide. Although much is known about CD4⁺ and CD8⁺ T cell responses to Mtb, the role of other T cell subsets is poorly understood. Invariant natural killer T (iNKT) cells are innate lymphocytes that express a semi-invariant T cell receptor and recognize lipid antigens presented by CD1d. Although iNKT cells participate in the immune response to many different pathogens, little is known about how iNKT cells directly kill microbes. We previously showed that when co-cultured with Mtb-infected macrophages, iNKT cells inhibit intracellular Mtb replication. Now, we used this model to dissociate the signals that induce iNKT cell activation markers including IFNγ production, from the signals that activate iNKT cell antimicrobial activity. This allowed us to uncover a novel antimicrobial effector function produced by iNKT cells: GM-CSF. GM-CSF is essential for immunity to Mtb, but its role has never been defined. This study is the first report to demonstrate a protective function of GM-CSF production by any T cell subset during Mtb infection. T cell production of GM-CSF should be considered as a potential mechanism of antimicrobial immunity.

The immune response in tuberculosis

There are 9 million cases of active tuberculosis reported annually; however, an estimated one-third of the world's population is infected with Mycobacterium tuberculosis and remains asymptomatic. Of these latent individuals, only 5-10% will develop active tuberculosis disease in their lifetime. CD4(+) T cells, as well as the cytokines IL-12, IFN-γ, and TNF, are critical in the control of Mycobacterium tuberculosis infection, but the host factors that determine why some individuals are protected from infection while others go on to develop disease are unclear. Genetic factors of the host and of the pathogen itself may be associated with an increased risk of patients developing active tuberculosis. This review aims to summarize what we know about the immune response in tuberculosis, in human disease, and in a range of experimental models, all of which are essential to advancing our mechanistic knowledge base of the host-pathogen interactions that influence disease outcome.

T Cell Activation and Proinflammatory Cytokine Production in Clinically Cured Tuberculosis Are Time-Dependent and Accompanied by Upregulation of IL-10

Background

Th1 cytokines are essential for the control of M. tuberculosis infection. The role of IL-10 in tuberculosis is controversial and there is an increasing body of evidence suggesting that the relationship between Th1 cytokines and IL-10 is not as antagonistic as it was first believed, and that these cytokines may complement each other in infectious diseases.

Methods

The present study evaluated the activating capacity of CD4+ and CD8+ T cell repertoire in response to antigen stimulation through the expression of CD69 using Flow Cytometry, as well as the functionality of PBMCs by determining the cytokine profile in patients with active tuberculosis and in clinically cured patients after in vitro stimulation using ELISA. Treated patients were subdivided according to time after clinical cure (<12 months or >12 months post-treatment).

Results

We observed that T cell activation was higher in TB-treated patients, especially CD8+ T cell activation in TB-Treated >1 year. Th1 cytokines were significantly higher in TB-Treated, and the levels of IFN-γ and TNF-α increased continuously after clinical cure. Moreover, IL-10 production was significantly higher in cured patients and it was also enhanced in cured patients over time after treatment. Th17, Th2 and Th22 cytokines showed no statistically significant differences between Healthy Donors, Active-TB and TB-Treated.

Conclusions

This study describes a scenario in which potentiation of CD4+ and CD8+ T cell activation and increased Th1 cytokine production are associated with the clinical cure of tuberculosis in the absence of significant changes in Th2 cytokine production and is accompanied by increased production of IL-10. In contrast to other infections with intracellular microorganisms, this response occurs later after the end of treatment.

Mycobacterium tuberculosis directs T helper 2 cell differentiation by inducing interleukin-1β production in dendritic cells

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), resides and replicates within phagocytes and persists in susceptible hosts by modulating protective innate immune responses. Furthermore, M. tuberculosis promotes T helper 2 (Th2) immune responses by altering the balance of T cell polarizing cytokines in infected cells. However, cytokines that regulate Th2 cell differentiation during TB infection remain unknown. Here we show that IL-1β, produced by phagocytes infected by virulent M. tuberculosis strain H37Rv, directs Th2 cell differentiation. In sharp contrast, the vaccine strain bacille Calmette-Guérin as well as RD-1 and ESAT-6 mutants of H37Rv failed to induce IL-1β and promote Th2 cell differentiation. Furthermore, ESAT-6 induced IL-1β production in dendritic cells (DCs), and CD4(+) T cells co-cultured with infected DCs differentiated into Th2 cells. Taken together, our findings indicate that IL-1β induced by RD-1/ESAT-6 plays an important role in the differentiation of Th2 cells, which in turn facilitates progression of TB by inhibiting host protective Th1 responses.

Prevalence, distribution and functional significance of the -237C to T polymorphism in the IL-12Rβ2 promoter in Indian tuberculosis patients

Cytokine/cytokine receptor gene polymorphisms related to structure/expression could impact immune response. Hence, the −237 polymorphic site in the 5′ promoter region of the IL-12Rβ2 (SNP ID: rs11810249) gene associated with the AP-4 transcription motif GAGCTG, was examined. Amplicons encompassing the polymorphism were generated from 46 pulmonary tuberculosis patients, 35 family contacts and 28 miscellaneous volunteers and sequenced. The C allele predominated among patients, (93.4%, 43/46), and in all volunteers and contacts screened, but the T allele was exclusively limited to patients, (6.5%, 3/46). The functional impact of this polymorphism on transcriptional activity was assessed by Luciferase-reporter and electrophoretic mobility shift assays (EMSA). Luciferase-reporter assays showed a significant reduction in transcriptional efficiency with T compared to C allele. The reduction in transcriptional efficiency with the T allele construct (pGIL-12Rb2-T), in U-87MG, THP-1 and Jurkat cell lines, were 53, 37.6, and 49.8% respectively, compared to the C allele construct (pGIL-12Rb2-C). Similarly, densitometric analysis of the EMSA assay showed reduced binding of the AP-4 transcription factor, to T compared to the C nucleotide probe. Reduced mRNA expression in all patients (3/3) harboring the T allele was seen, whereas individuals with the C allele exhibited high mRNA expression (17/25; 68%, p = 0.05). These observations were in agreement with the in vitro assessment of the promoter activity by Luciferase-reporter and EMSA assays. The reduced expression of IL-12Rβ2 transcripts in 8 patients despite having the C allele was attributed to the predominant over expression of the suppressors (IL-4 and GATA-3) and reduced expression of enhancers (IFN-α) of IL-12Rβ2 transcripts. The 17 high IL-12Rβ2 mRNA expressers had significantly elevated IFN-α mRNA levels compared to low expressers and volunteers. Notwithstanding the presence of high levels of IL-12Rβ2 mRNA in these patients elevated IFN-α expression could modulate their immune responses to Mycobacterium tuberculosis.

T cell responses to DosR and Rpf proteins in actively and latently infected individuals from Colombia

Mycobacterium tuberculosis DosR regulon-encoded proteins elicit strong immune T-cell responses in individuals with latent tuberculosis (LTBI). Also, resuscitation (Rpf) proteins can induce such responses. However, variations in the immunogenicity of the DosR and Rpf proteins have been observed in European and African populations, and no data are published from other geographic areas. In Colombian LTBI and patients with recently diagnosed PTB, we therefore studied the immune response to DosR, Rpf, stress, and nominal antigens from Mtb, in 7-day stimulated cultures. Three DosR (Rv1737c, Rv2029c, Rv2628c) and 2 Rpf (Rv0867 and Rv2389c) antigens were recognized most prominently on the basis of the net IFNγ production (DosR) or the percentage of responding individuals (Rpf). Results show that the selected DosR antigens induced a higher proportion of CD4-T cells producing IFNγ from LTBI, compared to pulmonary TB patients (PTB), while there were no differences in the proportion of CD8-T cells. An increased frequency of CD4, but not CD8 T-cells with a CD45RO(+)CD27(+) phenotype was observed in LTBI in response to Rv2029c, Rv0867c, and Rv2389c, compared to PTB. The levels of cytokines and chemokines in the supernatants of stimulated cells, showed that the DosR and Rpf antigens induced higher levels of IFNγ in cultures from LTBI compared to PTB, although the induced pattern of cytokines and chemokines was also antigen dependent. In summary, our results are consistent with the significant immunogenicity of Mtb DosR and Rpf antigens in LTBI individuals, and confirm and extend previously reported data from other TB affected human populations.

Early secreted antigen ESAT-6 of Mycobacterium tuberculosis promotes protective T helper 17 cell responses in a toll-like receptor-2-dependent manner

Despite its relatively poor efficacy, Bacillus Calmette-Guérin (BCG) has been used as a tuberculosis (TB) vaccine since its development in 1921. BCG induces robust T helper 1 (Th1) immune responses but, for many individuals, this is not sufficient for host resistance against Mycobacterium tuberculosis (M. tb) infection. Here we provide evidence that early secreted antigenic target protein 6 (ESAT-6), expressed by the virulent M. tb strain H37Rv but not by BCG, promotes vaccine-enhancing Th17 cell responses. These activities of ESAT-6 were dependent on TLR-2/MyD88 signalling and involved IL-6 and TGF-β production by dendritic cells. Thus, animals that were previously infected with H37Rv or recombinant BCG containing the RD1 region (BCG::RD1) exhibited improved protection upon re-challenge with virulent H37Rv compared with mice previously infected with BCG or RD1-deficient H37Rv (H37RvΔRD1). However, TLR-2 knockout (TLR-2⁻/⁻) animals neither showed Th17 responses nor exhibited improved protection in response to immunization with H37Rv. Furthermore, H37Rv and BCG::RD1 infection had little effect on the expression of the anti-inflammatory microRNA-146a (miR146a) in dendritic cells (DCs), whereas BCG and H37RvΔRD1 profoundly induced its expression in DCs. Consistent with these findings, ESAT-6 had no effect on miR146a expression in uninfected DCs, but dramatically inhibited its upregulation in BCG-infected or LPS-treated DCs. Collectively, our findings indicate that, in addition to Th1 immunity induced by BCG, RD1/ESAT-6-induced Th17 immune responses are essential for optimal vaccine efficacy.

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.

T-cell cytokines differentially control human monocyte antimicrobial responses by regulating vitamin D metabolism

We investigated the mechanisms by which T-cell cytokines are able to influence the Toll-like receptor (TLR)-induced, vitamin D-dependent antimicrobial pathway in human monocytes. T-cell cytokines differentially influenced TLR2/1-induced expression of the antimicrobial peptides cathelicidin and DEFB4, being up-regulated by IFN-γ, down-regulated by IL-4, and unaffected by IL-17. The Th1 cytokine IFN-γ up-regulated TLR2/1 induction of 25-hydroxyvitamin D-1α-hydroxylase (i.e., CYP27B1), leading to enhanced bioconversion of 25-hydroxyvitamin D(3) (25D(3)) to its active metabolite 1,25D(3). In contrast, the Th2 cytokine IL-4, by itself and in combination with the TLR2/1 ligand, induced catabolism of 25D(3) to the inactive metabolite 24,25D(3), and was dependent on expression of vitamin D-24-hydroxylase (i.e., CYP24A1). Therefore, the ability of T-cell cytokines to differentially control monocyte vitamin D metabolism represents a mechanism by which cell-mediated immune responses can regulate innate immune mechanisms to defend against microbial pathogens.

Tim3 binding to galectin-9 stimulates antimicrobial immunity

The interaction between Tim3 on Th1 cells and galectin-9 on Mycobacterium tuberculosis–infected macrophages restricts the bacterial growth by stimulating caspase-1–dependent IL-1β secretion.

T cell immunoglobulin and mucin domain 3 (Tim3) is a negative regulatory molecule that inhibits effector T_H1-type responses. Such inhibitory signals prevent unintended tissue inflammation, but can be detrimental if they lead to premature T cell exhaustion. Although the role of Tim3 in autoimmunity has been extensively studied, whether Tim3 regulates antimicrobial immunity has not been explored. Here, we show that Tim3 expressed on T_H1 cells interacts with its ligand, galectin-9 (Gal9), which is expressed by Mycobacterium tuberculosis–infected macrophages to restrict intracellular bacterial growth. Tim3–Gal9 interaction leads to macrophage activation and stimulates bactericidal activity by inducing caspase-1–dependent IL-1β secretion. We propose that the T_H1 cell surface molecule Tim3 has evolved to inhibit growth of intracellular pathogens via its ligand Gal9, which in turn inhibits expansion of effector T_H1 cells to prevent further tissue inflammation.

IFNG +874T/A polymorphism and cytokine plasma levels are associated with susceptibility to Mycobacterium tuberculosis infection and clinical manifestation of tuberculosis

Regarding the importance of interferon-gamma (IFN-gamma) in protective immunity against Mycobacterium tuberculosis and the functional role of IFNG +874T/A single nucleotide polymorphism (SNP) in the IFN-gamma production, the present study investigated the relationship of this genetic polymorphism with susceptibility to tuberculosis (TB). A total of 129 patients with pulmonary tuberculosis (PTB), 33 with extrapulmonary tuberculosis (EPTB), and 156 control subjects were studied. Blood samples were drawn and plasma was used to measure IFN-gamma serum concentration by enzyme-linked immunoassay. DNA samples were extracted from leukocytes and used to investigate +874T/A polymorphism in IFNG gene using allele-specific oligonucleotide-polymerase chain reaction. An association between the presence of the allele +874A and the genotype +874AA with the active tuberculosis was found (p < 0.0001, 95% confidence interval = 1.64-3.22), at the same time that allele + 874T and genotype +874T/T were more frequent in the control group. The average plasma concentration of IFN-gamma among patients with tuberculosis was significantly lower than in the control group, and were lower in the EPTB group than in the group with PTB, suggesting a relationship of low plasma levels of this cytokine with active tuberculosis and the progression to more serious forms of the disease. Furthermore, we observed the association of the +874T/T and +874A/A genotypes with high and low IFN-gamma plasma concentrations, respectively, both in TB patients and in the control groups. Thus our findings suggest an association of the IFNG +874T/A polymorphism with susceptibility to M. tuberculosis infection in the studied population.

Disparity in circulating peripheral blood dendritic cell subsets and cytokine profile of pulmonary tuberculosis patients compared with healthy family contacts

Dendritic cell (DC) subsets, myeloid DCs (mDCs), and plasmacytoid DCs (pDCs) play a fundamental role in immune response to Mycobacterium tuberculosis (M. tuberculosis). Flow-cytometric estimation of DC subsets showed differences in the ratio of these subsets in untreated, smear-positive pulmonary tuberculosis patients compared with healthy family contacts (HFC, p < 0.05). The percentage of pDCs (0.14 +/- 0.01) was higher than mDCs (0.12 +/- 0.01) in patients, whereas in HFC, mDCs (0.15 +/- 0.01) was higher than pDCs (0.1 +/- 0.01). The percentage of mDCs (0.15 +/- 0.01) and pDCs (0.11 +/- 0.01) was restored in treated patients. Alteration in the DC subsets before and after chemotherapy was confirmed in the follow-up of acid-fast bacilli (AFB)-positive patients. This reversal in the percentage of mDC vs pDCs implicates the influence of active disease on circulating DC subsets. The cytokine bead array revealed an inverse relationship in the circulating levels of IL-12 and IFN-gamma. High IL-12 (37.9 +/- 15.2) and low IFN-gamma (11.09 +/- 3.6) was seen in HFCs derived serum samples compared with that of patients (p < 0.05). The higher percentage of mDCs and elevated IL-12 levels was found to be associated with high risk HFCs investigated. Furthermore CpG/LPS-stimulated whole-blood culture of untreated patients expressed high IFN-alpha in pDCs and less IL-12 in mDCs compared with those of treated patients.

Mycobacterial antigen-induced T helper type 1 (Th1) and Th2 reactivity of peripheral blood mononuclear cells from diabetic and non-diabetic tuberculosis patients and Mycobacterium bovis bacilli Calmette-Guérin (BCG)-vaccinated healthy subjects

Patients with diabetes mellitus are more susceptible to tuberculosis (TB), and the clinical conditions of diabetic TB patients deteriorate faster than non-diabetic TB patients, but the immunological basis for this phenomenon is not understood clearly. Given the role of cell-mediated immunity (CMI) in providing protection against TB, we investigated whether CMI responses in diabetic TB patients are compromised. Peripheral blood mononuclear cells (PBMC) obtained from diabetic TB patients, non-diabetic TB patients and Mycobacterium bovis bacilli Calmette-Guérin (BCG)-vaccinated healthy subjects were cultured in the presence of complex mycobacterial antigens and pools of M. tuberculosis regions of difference (RD)1, RD4, RD6 and RD10 peptides. The PBMC were assessed for antigen-induced cell proliferation and secretion of T helper 1 (Th1) [interferon (IFN)-gamma, interleukin (IL)-2, tumour necrosis factor (TNF)-beta], and Th2 (IL-4, IL-5, IL-10) cytokines as CMI parameters. All the complex mycobacterial antigens and RD1(pool) stimulated strong proliferation of PBMC of all groups, except moderate responses to RD1(pool) in healthy subjects. In response to complex mycobacterial antigens, both IFN-gamma and TNF-beta were secreted by PBMC of all groups whereas diabetic TB patients secreted IL-10 with concentrations higher than the other two groups. Furthermore, in response to RD peptides, IFN-gamma and IL-10 were secreted by PBMC of diabetic TB patients only. The analyses of data in relation to relative cytokine concentrations showed that diabetic TB patients had lower Th1 : Th2 cytokines ratios, and a higher Th2 bias. The results demonstrate a shift towards Th2 bias in diabetic TB patients which may explain, at least in part, a faster deterioration in their clinical conditions.

Ex vivo cytokine mRNA levels correlate with changing clinical status of ethiopian TB patients and their contacts over time

There is an increasing body of evidence which suggests that IL-4 plays a role in the pathogenesis of TB, but a general consensus on its role remains elusive. We have previously published data from a cohort of Ethiopian TB patients, their contacts, and community controls suggesting that enhanced IL-4 production is associated with infection with M. tuberculosis, rather than overt disease and that long-term protection in infected community controls is associated with co-production of the IL-4 antagonist IL-4d2, alongside elevated IL-4. Here, for the first time, we compare data on expression of IFN-γ, IL-4 and IL-4δ2 over time in TB patients and their household contacts. During the follow-up period, the TB patients completed therapy and ceased to display TB-like symptoms. This correlated with a decrease in the relative amount of IL-4 expressed. Over the same period, the clinical status of some of their contacts also changed, with a number developing TB-like symptoms or clinically apparent TB. IL-4 expression was disproportionately increased in this group. The findings support the hypothesis that elevated IL-4 production is generally associated with infection, but that TB disease is associated with a relatively increased expression of IL-4 compared to IFN-γ and IL-4δ2. However, the data also suggest that there are no clear-cut differences between groups: the immune response over time appears to include changes in the expression of IFN-γ, IL-4 and IL-4δ2, and it is the relative, not absolute levels of cytokine expression that are characteristic of clinical status.

High levels of intracellular IL-4 are expressed in circulating apoptotic T cells in patients with tuberculosis and in community controls

Data concerning T helper cell phenotypes in response to Mycobacterium tuberculosis infection remain controversial. T lymphocyte intracellular interleukin-4 production in response to CD3 stimulation was determined by flow cytometry in 21 TB patients and 14 community controls. In supplementary experiments the association of interleukin-4 expression with apoptosis was investigated. A low percentage of CD4 T cells in both patients and controls expressed high levels of interleukin-4 (IL-4(high)). A larger subset of both CD4 and CD8 T cells of all subjects expressed low levels of intracellular IL-4 (IL-4(low)). Stimulated and unstimulated cells expressed IL-4(low) and IL-4(high). IL-4(low) percentages were lower in TB patients at diagnosis compared to controls while IL-4(high) percentages were higher in patients. Most IL-4(high) cells co-expressed active caspase-3, a marker for apoptosis. This co-expression was also shown in experimentally induced apoptotic Jurkat cells and peripheral blood neutrophils and monocytes. IL-4 levels may therefore not necessarily indicate a skewed Th cell phenotype, as our data suggest that IL-4 production by CD4 and CD8 T cells can occur constitutively in healthy controls with latent TB infection and in TB patients. Cellular IL-4 production may represent a normal cellular growth factor mechanism which is disturbed at the onset of apoptosis.

Changes in the kinetics of intracellular IFN-gamma production in TB patients during treatment

The role of T lymphocyte cytokine responses in tuberculosis (TB) still needs clarification. This study aimed to define interferon-gamma (IFN-gamma) responses longitudinally in HIV-negative TB patients during treatment, compared to those of healthy volunteers. Flow cytometric intracellular IFN-gamma determinations after CD3 stimulation were done in parallel with lymphocyte proliferation assays in response to mycobacterial antigen. Percentages of IFN-gamma-producing CD8 and CD4 T lymphocytes in patients at diagnosis were significantly higher than in controls but normalized during treatment. Additional kinetic studies suggested accelerated IFN-gamma production in patients at diagnosis, compared to controls and treated patients. Lymphocyte proliferation was below normal in patients at diagnosis and increased rapidly with decreasing bacterial load during treatment. We conclude that T cell IFN-gamma response kinetics in TB patients suggest a pre-activated state at diagnosis, which changes during treatment. At diagnosis intracellular IFN-gamma or lymphocyte proliferation was not an indicator for treatment response.

Spontaneous inflammatory cytokine gene expression in normal human peripheral blood mononuclear cells

Cytokines regulate cellular immune activity and are produced by a variety of cells, especially lymphocytes, monocytes, and macrophages. Measurement of cytokine levels has yielded useful information on the pathological process of different diseases such as AIDS, endotoxic shock, sepsis, asthma, and cancer. It may also be of use in the monitoring of disease progression and/or inflammation. To determine spontaneous cytokine gene expression in whole blood and PBMCs, whole blood was obtained from healthy volunteers and total mRNA was isolated from PBMCs. The kinetics of response were determined by sequential testing of cytokine gene expression by RT-PCR analysis. Our results demonstrated that isolated and incubated PBMCs expressed TNF-alpha and high levels of IL-1beta, IL-6, IL-8, and IL-10. In contrast, WB only expressed the mRNA cytokines of TNF-alpha and IL-8 (p < 0.05). These results suggest that spontaneous myriad mRNA cytokine expression can be avoided with the use of WB incubation and the rapid collection of PBMCs. Furthermore, this method should be employed in all cases where the levels of cytokine gene expression can be evaluated.

Modulation of gamma interferon receptor 1 by Mycobacterium tuberculosis: a potential immune response evasive mechanism

Mycobacterium tuberculosis inhibits gamma interferon (IFN-gamma)-mediated antimycobacterial action by adopting diverse mechanisms. IFN-gamma binds to its receptor, IFN-gammaR, in order to initiate proper signaling. We have observed reduced surface expression levels of IFN-gamma receptor 1 (IFN-gammaR1) in untreated pulmonary tuberculosis patients compared to those in healthy individuals (P < 0.01). Following antitubercular therapy, the expression of IFN-gammaR1 was restored in these patients. To delineate the mechanism by which M. tuberculosis modulates IFN-gammaR1, in vitro experiments were designed, wherein the down modulation of IFN-gammaR1 surface expression was observed for CD14+ cells in peripheral blood mononuclear cells (PBMCs) cocultured with live M. tuberculosis compared to that for uninfected cells (P < 0.01). No modulation of IFN-gammaR1 expression was observed for CD14+ cells in PBMCs infected with Mycobacterium smegmatis. A time-dependent decrease in IFN-gammaR1 mRNA expression was observed for PBMCs infected with M. tuberculosis. Similar down modulation of IFN-gammaR1 protein and mRNA expression in phorbol myristate acetate-differentiated THP-1 cells (pdTHP-1) by M. tuberculosis was observed (P < 0.01). Using reporter gene analysis of 5' deletion constructs of the IFN-gammaR1 gene (IFNGR1) promoter, the decrease in IFN-gammaR1 mRNA in M. tuberculosis-infected pdTHP-1 cells was shown to be due to the decreased transcription of IFNGR1. By immunoblotting and electrophoretic mobility shift assays, the down regulation of stimulating protein 1 (Sp1) expression and its recruitment on the phorbol ester-responsive element of the IFNGR1 promoter in M. tuberculosis-infected pdTHP-1 cells was observed. This down regulation of Sp1 in pdTHP-1 cells cocultured with M. tuberculosis may be responsible for the down regulation of IFN-gammaR1 expression, thereby potentially altering its receptivity to IFN-gamma.

Photodynamic therapy-generated tumor cell lysates with CpG-oligodeoxynucleotide enhance immunotherapy efficacy in human papillomavirus 16 (E6/E7) immortalized tumor cells

Immunotherapy with photodynamic therapy (PDT) offers great promise as a new alternative for cancer treatment; however, its use remains experimental. In this study, we examined the immunotherapeutic significance of human papillomavirus (HPV)-immortalized tumor cell lysates induced by PDT with CpG-oligodeoxynucleotide (ODN). PDT-cell lysates were generated by irradiating Radachlorin (5 microg/mL) preloaded TC-1 cells carrying HPV 16 E7. PDT-cell lysates plus ODN coinjection for protection against E7-expressing tumors as well as specific immune responses were evaluated with the following tests: heat shock protein 70 (HSP70) enzyme-linked immunosorbent assay, in vitro and in vivo tumor growth inhibition, interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) assay, cytotoxic T-lymphocyte assay, and fluorescence activated cell sorting (FACS) analysis. PDT-cell lysates plus ODN coinjection showed a significant suppression of tumor growth at both prophylactic and therapeutic levels, compared to PDT (or F/T)-cell lysates or ODN alone. In addition, we evaluated the level of the immune response with the coinjection. HSP70, an important regulator of inflammatory and immune response, was observed in abundance in the PDT-cell lysates. IFN-gamma production and cytotoxic T lymphocytes (CTL) responses were induced by PDT-cell lysates plus ODN injection. The coinjection resulted in PDT-cell lysate-specific antibodies (IgG1, IgG2a, IgG2b, and IgG3) and T-helper cell responses significantly higher than PDT-cell lysates alone. Moreover, IFN-gamma production and CTL responses were significantly induced in the PDT-cell lysate plus ODN immunized groups. These enhanced immune responses appeared to be mediated by CD8+ T cells only. These data suggest that PDT-cell lysates plus ODN injection may be an effective approach to induce CTL immune responses as a possible immunotherapeutic strategy for cancer therapy.

B7.2-/- mature dendritic cells generate T-helper 2 and regulatory T donor cells in fetal mice after in utero allogeneic bone marrow transplantation

In utero hematopoietic stem cell transplantation (IUT) results in limited chimerism and tolerance to alloantigens. We studied the relative role of B7.1 and B7.2 expression by dendritic cells (DCs) in engraftment and in generating donor-specific tolerance in fetal mice. Mature dendritic cells (mDCs) from B7.1(-/-) or B7.2(-/-) donors and wild-type (WT) lineage-depleted (lin(-)) C57BL/6 (B6) bone marrow (BM) were injected into BALB/c fetuses. Six weeks after IUT, B7.1(-/-) recipients had multilineage engraftment (4.7% +/- 0.8% T cells and 5.7% +/- 1.1% granulocytes) associated with graft-versus-host disease (GVHD) and decreased survival, but by 12 weeks only donor CD3(+) cells (2.1% +/- 1.3%) were present. Recipients of B7.2(-/-) mDCs and lin(-) WT B6 BM had exclusively CD3(+)CD4(+) T cells (11.8% +/- 8.5% at 6 weeks and 6.5% +/- 2.5% at 12 weeks). Most of the cells were T-helper 2, although 10.4% +/- 1.4% were of the T-regulatory (T(reg)) phenotype, ie, CD4(+)CD25(+). Donor T(reg) cells were detected both in the thymus and spleen, thus suggesting an effect on both central and peripheral immunity. The animals with T(reg) cells had better survival (82.3% versus 47.4%; P < .01) and no GVHD (0% versus 65%; P < .001). This group alone demonstrated multilineage engraftment of donor hematopoietic cells after postnatal transplantation with megadoses of donor lin(-) BM. Both the engrafted donor CD4(+)CD25(-) and CD4(+)CD25(+) cells induced comparable in vitro suppression of T-cell proliferation, thus suggesting their role in the persistence of the donor T cells in vivo. The CD4(+)CD25(-) cells produced interleukin 10 or interleukin 4 and were inhibited by anti-T-helper 2 cytokine-neutralizing antibodies, whereas the CD4(+)CD25(+) cells showed no evidence of any involvement of a cytokine-like soluble mediator and expressed cytotoxic T-lymphocyte antigen 4 (CTLA-4) and foxp3 constitutively. Donor mDCs and donor CD4 T cells were detected among the thymocytes of the recipients of B7.2(-/-) mDCs and lin(-) WT B6 BM. Thus, it seems that costimulatory molecule expression of donor DCs can play a significant immunomodulatory role in survival, GVHD, engraftment, and homing of allogeneic BM cells after IUT through the generation of T(reg) cells.

Th2-type immune response observed in healthy individuals to sonicate antigen prepared from the most prevalentMycobacterium tuberculosisstrain with single copy of IS6110

Different Mycobacterium tuberculosis strains operate different immune evasion strategies for their survival in the host. This mainly depends on the virulence of the strain and the host immune responses. The most virulent strains are actively involved in the transmission, widely spread in the community and induce differential immune responses. We evaluated the immune response of a sonicate antigen prepared from one predominant strain (S7) from M. tuberculosis harbouring a single copy of IS6110. Significant lymphoproliferative response against purified protein derivative from tubercle bacillus (PPD) and H37Rv antigens was observed in PPD positive normal individuals and tuberculosis patients. Interferon-gamma (IFN-gamma) levels against these antigens were significantly increased in normal individuals but not in tuberculosis patients. The antigen S7 showed marginal T-cell proliferation but did not induce IFN-gamma secretion in both groups. Conversely, it induced significantly high levels of cytokine interleukin 4 (IL-4) in normal individuals. The macrophage cytokines, IL-12 and tumour necrosis factor alpha (TNF-alpha), did not show S7 antigen specific stimulation. The intracellular cytokine further confirmed an increase in IL-4(+)/CD4+ T-cells and a decrease in IFN-gamma(+)/CD4+ T-cells upon stimulation. The antibody response showed an increase in IgG and IgA levels against this antigen in normal individuals. These observations suggest that antigen S7 modulates the immune response towards T helper cell type 2 by suppressing T helper cell type 1 protective immune response in PPD positive normal individuals. We speculate that some components of this sonicate antigen are associated with immunosuppressive response.

CD69 expression on CD4+ T lymphocytes after in vitro stimulation with tuberculin is an indicator of immune sensitization against Mycobacterium tuberculosis antigens

The expression of the CD69 antigen on CD4 T lymphocytes after in vitro stimulation with purified protein derivative (2 tuberculin units) was used to evaluate the tuberculin reactivities of 52 individuals from four experimental groups: Mycobacterium bovis BCG-vaccinated healthy individuals with a negative tuberculin skin test (TST) result (group A), BCG-vaccinated healthy individuals with a positive TST result (group B), patients with active tuberculosis (TB) before treatment (group C), and individuals with clinically inactive TB who had previously completed a prescribed course of chemotherapy (group D). The expression of CD69 on CD4 T lymphocytes was significantly higher in patients with active TB (16.2%+/-7.3%), individuals with clinically inactive TB (10.5%+/-7.4%), and healthy individuals with a positive TST result (15.5%+/-7.2%) than in healthy individuals with a negative TST result (3.8%+/-4.3%) (P<0.005). We confirmed the correlation between CD69 antigen expression on T lymphocytes after stimulation with tuberculin and the TST induration diameter (Spearman rho=0.783; P<0.001), an assay for gamma interferon (the Quantiferon-TB assay; Spearman rho=0.613; P<0.001), and the lymphocyte BLAST transformation test (Spearman rho=0.537; P<0.001). Our results demonstrate the usefulness of the determination of CD69 on CD4 T lymphocytes after in vitro stimulation with tuberculin as a rapid indicator of immune sensitization against Mycobacterium tuberculosis.

Mycobacterium tuberculosis as viewed through a computer

Mathematical models are emerging as important tools in the study of microbiology. As an illustrative example, we present results from several models each generated to study the interaction of Mycobacterium tuberculosis and the immune system. Different mathematical models were formulated on the basis of assumptions regarding system-component interactions, enabling us to explore specific aspects at diverse biological scales (e.g. intracellular, cell-cell interactions, and cell population dynamics). In addition, we were able to examine both temporal and spatial aspects. At each scale, there were consistent themes that emerged as determinative in infection outcome. Factors we identified include both host and microbial characteristics. The use of the models lies in generating hypotheses that can then be tested experimentally. Here, we outline the primary host and bacterial factors that we have identified as key mechanisms that contribute to the success of M. tuberculosis as a human pathogen. Our goal is to stimulate experimentation and foster collaborations between theoretical and experimental scientists.

Monocyte cytokine secretion in patients with pulmonary tuberculosis differs from that of healthy infected subjects and correlates with clinical manifestations

Cell-mediated immunity, leading to Mycobacterium tuberculosis (Mtb)-constraining granuloma formation, is the major component of host defense against tuberculosis and is regulated by the balance of cytokines secreted mostly by mononuclear phagocytes and lymphocytes. To better understand the role of monocytes in the regulation of the immune response against pulmonary tuberculosis, we examined IL-10, IL-12 and TNF-alpha release by monocytes from healthy purified protein derivative (PPD) reactors and pulmonary tuberculosis patients with or without systemic reactions (e.g., fever, weight loss, asthenia). Our study shows that, probably as a result of in vivo priming by circulating antigens, monocytes from patients, especially those with systemic manifestations, have a biased ex vivo cytokine secretion, with high IL-10 and TNF-alpha but low IL-12, in contrast with PPD reactors. Higher spontaneous IL-10 and TNF-alpha release persisted when monocytes were co-cultured with autologous lymphocytes. Challenge of patients' monocytes with a virulent Mtb strain led to a further enhancement of IL-10 and TNF-alpha, but not of IL-12. When lymphocytes were added to these cultures, IL-10 and TNF-alpha elevation persisted and, in the patients with a systemic reaction, both IL-12 and IFN-gamma were significantly reduced compared to PPD reactors. Intragroup comparisons revealed that in the patients with systemic reactions, the lymphocyte-monocyte interaction resulted in a positive feedback for IL-10 secretion, while in the patients without systemic reaction and PPD reactors, the feedback was positive for IL-12 secretion. Thus, in tuberculosis, there appears to exist a relationship between the immunological findings and the distinct clinical manifestations.

Cell-mediated immune responses in children towards secreted proteins of Mycobacterium bovis BCG

BACKGROUND

There is a need to develop an improved anti-TB vaccine for adequate control and elimination of tuberculosis, to control the spread of MDR-TB and TB/HIV co-infection. Studies in children have indicated that BCG vaccination has certain beneficial effects, especially against miliary TB and TB meningitis, but needs to be improved for protection against pulmonary tuberculosis.

OBJECTIVE

The aim of the present study was to identify the immunogenic proteins in the culture filtrate (CF) of Mycobacterium bovis BCG by studying the effector mechanism of protection in children, which may help in the formulation of an effective vaccine against tuberculosis.

MATERIALS AND METHODS

Lymphoproliferative responses (LTT) and the levels of IL-2 and IFN-gamma (Th1 cytokines) released into the culture supernatants were estimated (by ELISA) in short-term cultures of PBMC of BCG vaccinated (n=25) and unvaccinated (n=15) children and children with tuberculosis (n=15) against 10 different fractions of CF (mol.wt > or = 90-<14 kDa).

RESULTS

The mean stimulation indices (SI) in LTT against all the (10) fractions in vaccinated children were high when compared to the unvaccinated and diseased groups; however, of the 10 fractions, F3, F4, F6, F8 and F9 elicited significantly higher SIs than the other fractions (p<0.05). In the vaccinated children, the SI (5.58+/-1.57), levels of IL-2 (381.66+/-16.40 pg/ml) and IFN-gamma (732+/-62.36 pg/ml) in the cultures stimulated by fraction 8 (34-30k Da) were significantly higher (p<0.001), than responses to the other fractions and also to those of other groups of children.

CONCLUSION

Thus, the peptides within the cluster 34-30 kDa appear to be promising vaccine candidates by virtue of their immunodominant nature specifically priming Th1 cells in normal, BCG-vaccinated children.

The human immune response to Mycobacterium tuberculosis in lung and lymph node

A key issue for the study of tuberculosis is to understand why individuals infected with Mycobacterium tuberculosis (Mtb) experience different clinical outcomes. To better understand the dynamics of Mtb infection and immunity, we have previously developed a temporal mathematical model that qualitatively and quantitatively characterizes the cellular and cytokine control network during infection. In this work we extend that model to a two compartmental model to capture the important processes of cellular activation and priming that occur between the lung and the nearest draining lymph node. We are able to reproduce typical disease progression scenarios including primary infection, latency or clearance. Then we use the model to predict key processes determining these different disease trajectories (i.e. identify bifurcation parameters), suggesting directions for further basic science study and potential new treatment strategies.

Recent advances in tuberculosis research in India

Tuberculosis (TB) continues to be the leading killer of mankind among all infectious diseases, especially in the developing countries. Since the discovery of tubercle bacillus more than 100 years ago, TB has been the subject of research in an attempt to develop tools and strategies to combat this disease. Research in Indian laboratories has contributed significantly towards developing the DOTS strategy employed worldwide in tuberculosis control programmes and elucidating the biological properties of its etiologic agent, M. tuberculosis. In recent times, the development of tools for manipulation of mycobacteria has given a boost to researchers working in this field. New strategies are being employed towards understanding the mechanisms of protection and pathogenesis of this disease. Molecular methods are being applied to develop new tools and reagents for prevention, diagnosis and treatment of tuberculosis. With the sequencing of the genome of M. tuberculosis, molecules are being identified for the development of new drugs and vaccines. In this chapter, the advances made in these areas by Indian researchers mainly during the last five years are reviewed.

Immunopathogenesis of chlamydia trachomatis infections in women

OBJECTIVE

To develop a model of pathogenesis by which Chlamydia trachomatis progresses from acute to chronic infection, and finally serious disease (salpingitis, tubal occlusion).

DESIGN

Review of current literature located through web-based Medline searches using key words: Chlamydia trachomatis, immunology, cytokines, heat shock protein, infertility.

RESULT(S)

Cell-mediated immune mechanisms appear to be critical in determining whether acute infection is resolved or progresses into chronicity with pathological outcome. What determines the particular immune pathway depends on a range of determinants-HLA subtype and human genetics, cytokine profile, infectious load, route of infection, and endocrinology. A clearer picture of the natural history of chlamydial pathology may assist in providing better predictors of those women who may go on to develop significant sequelae after infection.

CONCLUSION(S)

Predicting those who may develop serious disease, including infertility, may contribute to improved management of such persons during earlier stages of infection and assist in prevention.

Spontaneous cytokine production and its effect on induced production

Cytokines regulate cellular immune activity and are produced by a variety of cells, especially lymphocytes, monocytes, and macrophages. Multiparameter flow cytometry is often used to examine cell-specific cytokine production after in vitro phorbol 12-myristate 13-acetate and ionomycin induction, with brefeldin A or other agents added to inhibit protein secretion. Spontaneous ex vivo production reportedly rarely occurs. We examined the spontaneous production of interleukin 2 (IL-2), IL-4, IL-6, IL-8, IL-10, tumor necrosis factor alpha (TNF-alpha), and gamma interferon (IFN-gamma) by peripheral-blood B lymphocytes, T cells, CD8(-) T cells, CD8(+) T cells, CD3(-) CD16/56(+) lymphocytes (natural killer [NK] cells), CD3(+) CD16/56(+) lymphocytes (natural T [NT] cells), and/or monocytes of 316 acutely ill hospitalized persons and 62 healthy adults in Malawi, Africa. We also evaluated the relationship between spontaneous and induced cytokine production. In patients, spontaneous TNF-alpha production occurred most frequently, followed in descending order by IFN-gamma, IL-8, IL-4, IL-10, IL-6, and IL-2. Various cells of 60 patients spontaneously produced TNF-alpha; for 12 of these patients, TNF-alpha was the only cytokine produced spontaneously. Spontaneous cytokine production was most frequent in the immunoregulatory cells, NK and NT. For IL-2, IL-4, IL-6, IL-8, and IL-10, spontaneous cytokine production was associated with greater induced production. For TNF-alpha and IFN-gamma, the relationships varied by cell type. For healthy adults, IL-6 was the cytokine most often produced spontaneously. Spontaneous cytokine production was not unusual in these acutely ill and healthy persons living in an area where human immunodeficiency virus, mycobacterial, malaria, and assorted parasitic infections are endemic. In such populations, spontaneous, as well as induced, cell-specific cytokine production should be measured and evaluated in relation to various disease states.

Decreased IFN- gamma and increased IL-4 production by human CD8(+) T cells in response to Mycobacterium tuberculosis in tuberculosis patients

To investigate the role of MHC class I restricted CD8(+) T cells in host defense to M. tuberculosis, peripheral blood mononuclear cells (PBMC) from healthy BCG-vaccinated donors and untreated pulmonary tuberculosis (TB) patients in The Gambia were stimulated for 6 days with M. bovis BCG or M. tuberculosis and the CD8(+) T cell response analyzed. Intracellular FACS analysis of cytokine production by CD8(+) T cells showed that IFN- gamma and TNF- alpha production were greatly reduced in TB patients compared to healthy controls. IL-4-producing CD8(+) T cells were detected in TB patients, a phenotype absent in controls. Collectively, these data suggest that an alteration in the type 1/type 2 cytokine balance occurs in CD8(+) T cells during clinical tuberculosis, and that this may provide a surrogate marker for disease.

Innate immunity to Mycobacterium tuberculosis

The different manifestations of infection with Mycobacterium tuberculosis reflect the balance between the bacillus and host defense mechanisms. Traditionally, protective immunity to tuberculosis has been ascribed to T-cell-mediated immunity, with CD4(+) T cells playing a crucial role. Recent immunological and genetic studies support the long-standing notion that innate immunity is also relevant in tuberculosis. In this review, emphasis is on these natural, innate host defense mechanisms, referring to experimental data (e.g., studies in gene knockout mice) and epidemiological, immunological, and genetic studies in human tuberculosis. The first step in the innate host defense is cellular uptake of M. tuberculosis, which involves different cellular receptors and humoral factors. Toll-like receptors seem to play a crucial role in immune recognition of M. tuberculosis, which is the next step. The subsequent inflammatory response is regulated by production of pro- and anti-inflammatory cytokines and chemokines. Different natural effector mechanisms for killing of M. tuberculosis have now been identified. Finally, the innate host response is necessary for induction of adaptive immunity to M. tuberculosis. These basic mechanisms augment our understanding of disease pathogenesis and clinical course and will be of help in designing adjunctive treatment strategies.

Comparative and prospective study of different immune parameters in healthy subjects at risk for tuberculosis and in tuberculosis patients

It has not been fully elucidated which of the components of the immune response against Mycobacterium tuberculosis is indicative of resistance or susceptibility. The aim of this study was to identify an immune parameter that could be indicative of either resistance or susceptibility to M. tuberculosis infection. We prospectively studied (three determinations, at months 0, 8, and 12) 15 patients with chronic pulmonary tuberculosis and 42 healthy individuals with a recent and frequent contact with tuberculosis patients. Peripheral blood mononuclear cells were stimulated with a whole-protein extract or the 30-kDa antigen of M. tuberculosis for 6 days, and several immune parameters were determined. No consistent differences between tuberculosis patients and healthy controls were detected in most immune parameters studied, including the expression of different activation antigens, cytokine secretion, lymphocyte proliferation, and nitric oxide production. However, the synthesis of tumor necrosis factor alpha, the intracellular detection of gamma interferon, and the apoptosis of monocytes under certain culture conditions tended to show clear-cut differences in cells from patients and controls (P < 0.05 in all cases for most determinations). Nevertheless, when results were analyzed on an individual basis, it was evident that a significant degree of overlapping of values from patients and controls occurred for all parameters studied. We conclude that although the immune parameters tested do not allow the identification of individuals susceptible to M. tuberculosis, the specificity and sensitivity of some of them could be improved through future studies.

Immunology of tuberculosis

The resurgence of tuberculosis worldwide has intensified research efforts directed at examining the host defense and pathogenic mechanisms operative in Mycobacterium tuberculosis infection. This review summarizes our current understanding of the host immune response, with emphasis on the roles of macrophages, T cells, and the cytokine/chemokine network in engendering protective immunity. Specifically, we summarize studies addressing the ability of the organism to survive within macrophages by controlling phagolysosome fusion. The recent studies on Toll-like receptors and the impact on the innate response to M. tuberculosis are discussed. We also focus on the induction, specificity, and effector functions of CD4(+) and CD8(+) T cells, and the roles of cytokines and chemokines in the induction and effector functions of the immune response. Presentation of mycobacterial antigens by MHC class I, class II, and CD1 as well as the implications of these molecules sampling various compartments of the cell for presentation to T cells are discussed. Increased attention to this disease and the integration of animal models and human studies have afforded us a greater understanding of tuberculosis and the steps necessary to combat this infection. The pace of this research must be maintained if we are to realize an effective vaccine in the next decades.

Contribution of CD8(+) T cells to gamma interferon production in human tuberculosis

The proportions of peripheral blood mononuclear cells (PBMC), CD4(+) T cells, and CD8(+) T cells that produce gamma interferon (IFN-gamma) in response to Mycobacterium tuberculosis were markedly reduced in tuberculosis patients, particularly in those with severe disease. Depletion of CD4(+) but not CD8(+) cells prior to stimulation of PBMC with M. tuberculosis abolished IFN-gamma production. These results show that (i) IFN-gamma production by CD8(+) and CD4(+) cells correlates with the clinical manifestations of M. tuberculosis infection and (ii) IFN-gamma production by CD8(+) cells depends on CD4(+) cells.