The relative importance of T cell subsets in immunity and immunopathology of airborne Mycobacterium tuberculosis infection in mice

Role for nucleotide excision repair in virulence of Mycobacterium tuberculosis

Mutations in Mycobacterium tuberculosis uvrB result in severe sensitivity to acidified nitrite, a source of nitric oxide (6). In this study, we show that a uvrB mutant is exquisitely sensitive to UV light but not to several sources of reactive oxygen species in vitro. Furthermore, a uvrB mutant was attenuated in mice as judged by an extension of life span. Attenuation in mice was partially reversed by genetic inactivation of nitric oxide synthase 2 (iNOS) and almost completely reversed in mice lacking both iNOS and phagocyte oxidase. Thus, a gene predicted to encode a key element of DNA repair is required for resistance of M. tuberculosis to both reactive nitrogen and reactive oxygen species in mice.

Lethality of quinolones against Mycobacterium smegmatis in the presence or absence of chloramphenicol

Quinolones were examined for rapid lethal activity against Mycobacterium smegmatis in the presence and absence of chloramphenicol, an inhibitor of protein synthesis. C-8 methoxy, C-6 fluorine, and particular C-7 ring substituents enhanced rapid killing. With the surprising exception of moxifloxacin, higher quinolone concentrations were required for lethal activity in the presence of chloramphenicol than in its absence. Moxifloxacin was also unusual in lacking the time lag characteristic of fluoroquinolone lethality. Several fluoroquinolone dimers, which represent quinolones with large C-7 substituents, showed modest bacteriostatic activity. Unlike other quinolones, the dimers failed to display lethal activity. The insensitivity of moxifloxacin to chloramphenicol has not been observed with other bacteria and may therefore reflect unique aspects of mycobacterial gyrase.

The influence of age on immunity to infection with Mycobacterium tuberculosis

Changes within the immune system during aging lead to an elderly population that is both highly susceptible to infectious diseases and unresponsive to typical vaccine protocols. Using the murine model of tuberculosis, we have identified key differences in the generation of T-helper 1 cell immunity between old and young mice, and this information may be important for the design of new vaccines or post exposure therapies to protect the elderly against infectious diseases. In response to infection with Mycobacterium tuberculosis, it has been shown that the generation of antigen-specific CD4(+) T-cell immunity is impaired in old mice. In contrast, recent findings document that old mice display a transient enhanced resistance that occurs within the first 3 weeks of infection. Early resistance was associated with the presence of CD8(+) T cells and their ability to produce interferon-gamma (IFN-gamma) well before their young counterparts. Further investigation into the mechanism by which CD8(+) T cells are induced to secrete IFN-gammain vivo could provide an approach to enhance the effector function of these cells and subsequently protect elderly individuals from respiratory pathogens such as M. tuberculosis.

Properties and protective value of the secondary versus primary T helper type 1 response to airborne Mycobacterium tuberculosis infection in mice

Mice immunized against Mycobacterium tuberculosis (Mtb) infection by curing them of a primary lung infection were compared with naive mice in terms of the ability to generate a Th1 cell immune response and to control growth of an airborne Mtb challenge infection. Immunized mice generated and expressed Th1 cell immunity several days sooner than naive mice, as demonstrated by an earlier increase in the synthesis in the lungs of mRNA for Th1 cytokines and for inducible nitric oxide synthase, an indicator of macrophage activation. This Th1 cytokine/mRNA synthesis was accompanied by an earlier accumulation of Mtb-specific Th1 cells in the lungs and the presence of CD4 T cells in lesions. An earlier generation of immunity was associated with an earlier inhibition of Mtb growth when infection was at a 1-log lower level. However, inhibition of Mtb growth in immunized, as well as in naive, mice was not followed by resolution of the infection, but by stabilization of the infection at a stationary level. The results indicate that there is no reason to believe that the secondary response to an Mtb infection is quantitatively or qualitatively superior to the primary response.

Investigation of antigen-specific T-cell responses and subcutaneous granuloma development during experimental sensitization of calves with Mycobacterium avium subsp paratuberculosis

OBJECTIVE

To characterize the early cellular immune response to Mycobacterium avium subsp paratuberculosis (MAP) infection and evaluate the development of granulomatous inflammation at the SC injection site in experimentally inoculated calves.

ANIMALS

Forty-eight 4-week-old calves.

PROCEDURE

Calves received an SC injection of MAP strain 19698 (n = 25), sterile saline (0.9% NaCl) solution (20), or a commercial paratuberculosis vaccine (3); the inoculation site tissue and associated draining lymph node were excised at postinoculation day (PID) 0 (n = 36), 7 (14), 14 (6), 21 (8), and 60 (32). Sections of inoculation site tissues were evaluated immunohistochemically for T-cell subsets; lymph node mononuclear cells (LNMCs) were assessed for T-cell surface markers and for intracellular interferon-gamma via flow cytometry.

RESULTS

At MAP inoculation sites, calves developed mild, focal granulomatous inflammation by PID 7; by PID 60, areas of inflammation contained macrophages with numerous lymphocytes. Compared with control calves, there was increased antigen-specific LNMC proliferation in MAP- and vaccine-inoculated calves at PID 60, although proliferation among lymphocyte subsets was not significantly different between MAP-inoculated and control calves; in vaccine-inoculated calves, CD4+ T-cells predominated. In MAP-inoculated and control calves, antigen-specific interferon-gamma production by LNMCs did not differ significantly; vaccine-inoculated calves had marked interferon-gamma expression by CD4+ T-cells.

CONCLUSIONS AND CLINICAL RELEVANCE

In calves, SC administration of MAP resulted in granulomatous inflammation at inoculation sites and an antigen-specific T-cell proliferative response. Results suggest that this experimental system can be used to reproducibly generate antigen-specific T-cells during MAP infection for functional analysis.

The IL-27 receptor chain WSX-1 differentially regulates antibacterial immunity and survival during experimental tuberculosis

IL-12 is a potent inducer of IFN-gamma production and promotes a protective cell-mediated immune response after Mycobacterium tuberculosis infection. Recently, the IL-12-related cytokine IL-27 was discovered, and WSX-1 was identified as one component of the IL-27R complex. To determine the functional significance of IL-27/WSX-1 during tuberculosis, we analyzed the course of infection and the immune response in WSX-1-KO mice after aerosol infection with M. tuberculosis. In the absence of WSX-1, an increased production of the proinflammatory cytokines TNF and IL-12p40 resulted in elevated CD4+ T cell activation and IFN-gamma production, which enhanced macrophage effector functions and reduced bacterial loads. This is the first occasion of a selectively gene-deficient mouse strain showing higher levels of protective immunity against M. tuberculosis infection than wild-type mice. However, a concomitantly increased chronic inflammatory response also accelerated death of infected WSX-1-KO mice. In vitro, IL-27 induced STAT3 phosphorylation and inhibited TNF and IL-12 production in activated peritoneal macrophages, indicating a novel feedback mechanism by which IL-27 can modulate excessive inflammation. In conclusion, IL-27 both prevents optimal antimycobacterial protection and limits the pathological sequelae of chronic inflammation.

New models for the study of Mycobacterium-host interactions

The outcome of Mycobacterium infection is determined by a series of complex interactions between the bacteria and host immunity. Traditionally, mammalian models and cultured cells have been used to study these interactions. Recently, ameba (Dictyostelium), fruit flies (Drosophila) and zebrafish, amenable to forward genetic screens, have been developed as models for mycobacterial pathogenesis. Infection of these hosts with mycobacteria has allowed the dissection of intracellular trafficking pathways (Dictyostelium) and the roles of phagocytic versus antimicrobial peptide responses (Drosophila). Real-time visualization of the optically transparent zebrafish embryo/larva has elucidated mechanisms by which Mycobacterium-infected leukocytes migrate and subsequently aggregate into granulomas, the hallmark pathological structures of tuberculosis.

Role of CD8+ T lymphocytes in control of Mycobacterium tuberculosis infection

Tuberculosis remains a global health concern. Control of infection is dependent on cell-mediated immune responses, with CD4+ T lymphocytes playing a central role. In this article, data supporting the importance of CD8+ T lymphocytes is reviewed, with an emphasis on the unique functional roles that this lymphocyte subset may play.

Long-term protection against tuberculosis following vaccination with a severely attenuated double lysine and pantothenate auxotroph of Mycobacterium tuberculosis

We report the safety and immunogenicity of a double lysine and pantothenate auxotroph of Mycobacterium tuberculosis in mice. The DeltalysA DeltapanCD mutant is completely attenuated in immunocompromised SCID and gamma interferon knockout mice yet induces short-term and long-term protection in immunocompetent and CD4-deficient mice following single-dose subcutaneous vaccination.

Responses against complex antigens in various models of CD4 T-cell deficiency: surprises from an anti-CD4 antibody transgenic mouse

The most common models of CD4 T-cell deficiency are mice exogenously injected with anti-CD4 antibody (Ab), CD4 knockout (CD4-/-) and major histocompatibility complex (MHC) class II knockout (class II-/-) mice. We recently described the anti-CD4 Ab transgenic mouse (GK) as an improved CD4 cell-deficient model. This review compares this new GK mouse model with the widely available class II-/- and CD4-/- mice, when exposed to complex antigens (foreign grafts and during bacterial or viral infection). We highlight here the cytometric and functional differences (including Ab isotype, viral or bacterial clearance, and graft survival) among these CD4 cell-deficient models. For example, whereas grafts are generally rejected in class II-/- and CD4-/- mice as quickly as in wild-type mice, they survive longer in GK mice. Also, CD4-/- mice produce IgG against both simple model and complex antigens, but class II-/- and GK mice produce small amounts of IgG2a against complex antigens but not simple model antigens. These differences harbinger the caveats in the use of these various mice.

The major histocompatibility complex haplotype affects T-cell recognition of mycobacterial antigens but not resistance to Mycobacterium tuberculosis in C3H mice

Both innate and adaptive immunity play an important role in host resistance to Mycobacterium tuberculosis infection. Although several studies have suggested that the major histocompatibility complex (MHC) haplotype affects susceptibility to infection, it remains unclear whether the modulation of T-cell immunity by the MHC locus determines the host's susceptibility to tuberculosis. To determine whether allelic differences in the MHC locus affect the T-cell immune response after M. tuberculosis infection, we infected inbred and H-2 congenic mouse strains by the respiratory route. The H-2 locus has a profound effect on the antigen-specific CD4+-T-cell response after M. tuberculosis infection. CD4+ T cells from infected mice of the H-2(b) haplotype produced more gamma interferon (IFN-gamma) after in vitro stimulation with mycobacterial antigens than mice of the H-2(k) haplotype. A higher level of IFN-gamma was also detected in bronchoalveolar lavage fluid from infected mice of the H-2(b) haplotype. Furthermore, C3.SW-H2(b)/SnJ mice generate and recruit activated T cells to the lung after infection. Despite a robust immune response, C3.SW-H2(b)/SnJ mice succumbed to infection early and were similarly susceptible to infection as other C3H (H-2(k)) substrains. These results suggest that although the MHC haplotype has a profound impact on the T-cell recognition of M. tuberculosis antigens, the susceptibility of C3H mice to infection is MHC independent.

Clinical latency and reactivation of AIDS-related mycobacterial infections

The immune mechanisms associated with the evolution from latent to clinically active mycobacterial coinfection in human immunodeficiency virus type 1 (HIV-1)-infected humans remain poorly understood. Previous work has demonstrated that macaques infected with simian immunodeficiency virus (SIVmac) can develop persistent Mycobacterium bovis BCG coinfection and a fatal SIV-related tuberculosis-like disease by 4 months after BCG inoculation. In the present study, SIVmac-infected monkeys that developed clinically quiescent mycobacterial infection after BCG inoculation were followed prospectively for the reactivation of the BCG and the development of SIV-related tuberculosis-like disease. The development of clinically latent BCG coinfection in these SIVmac-infected monkeys was characterized by a change from high to undetectable levels of bacterial organisms, with or without measurable BCG mRNA expression in lymph node cells. The reactivation of clinically latent BCG coinfection and development of SIV-related tuberculosis-like disease were then observed in these SIVmac-BCG-coinfected monkeys during a 21-month period of follow-up. The reactivation of SIV-related tuberculosis-like disease in these animals coincided with a severe depletion of CD4 T cells and a loss of BCG-specific T-cell responses. Interestingly, bacterial superantigen challenge of the SIVmac-BCG-coinfected monkeys resulted in an up-regulation of clinically latent BCG coinfection, suggesting that infection with superantigen-producing microbes may increase the susceptibility of individuals to the reactivation of AIDS-related mycobacterial coinfection. Thus, reactivation of latent mycobacterial infections in HIV-1-infected individuals may result from a loss of T-cell immunity or from a superimposed further compromise of the immune system.

Iron and microbial infection

The use of iron as a cofactor in basic metabolic pathways is essential to both pathogenic microorganisms and their hosts. It is also a pivotal component of the innate immune response through its role in the generation of toxic oxygen and nitrogen intermediates. During evolution, the shared requirement of micro- and macroorganisms for this important nutrient has shaped the pathogen-host relationship. Here, we discuss how pathogens compete with the host for iron, and also how the host uses iron to counteract this threat.

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.

CD4 T cells producing IFN-gamma in the lungs of mice challenged with mycobacteria express a CD27-negative phenotype

Protection against tuberculosis depends upon the generation of CD4(+) T cell effectors capable of producing IFN-gamma and stimulating macrophage antimycobacterial function. Effector CD4(+) T cells are known to express CD44(hi)CD62L(lo) surface phenotype. In this paper we demonstrate that a population of CD44(hi)CD62L(lo) CD4(+) effectors generated in response to Mycobacterium bovis BCG or M. tuberculosis infection in C57BL/6 mice is heterogeneous and consists of CD27(hi) and CD27(lo) T cell subsets. These subsets exhibit a similar degree of in vivo proliferation, but differ by the capacity for IFN-gamma production. Ex vivo isolated CD27(lo) T cells express higher amounts of IFN-gamma RNA and contain higher frequencies of IFN-gamma producers compared to CD27(hi) subset, as shown by real-time PCR, intracellular staining for IFN-gamma and ELISPOT assays. In addition, CD27(lo) CD4(+) T cells uniformly express CD44(hi)CD62L(lo) phenotype. We propose that CD27(lo) CD44(hi)CD62L(lo) CD4(+) T cells represent highly differentiated effector cells with a high capacity for IFN-gamma secretion and antimycobacterial protection at the site of infection.

Activation of CD8 T cells by mycobacterial vaccination protects against pulmonary tuberculosis in the absence of CD4 T cells

We have investigated whether both primary CD8 T cell activation and CD8 T cell-mediated protection from Mycobacterium tuberculosis challenge could occur in mycobacterial-vaccinated CD4 T cell-deficient (CD4KO) mice. Different from wild-type C57BL/6 mice, s.c. vaccination with bacillus Calmette-Guérin (BCG) in CD4KO mice failed to provide protection from secondary M. tuberculosis challenge at 3 wk postvaccination. However, similar to C57BL/6 mice, CD4KO mice were well protected from M. tuberculosis at weeks 6 and 12 postvaccination. This protection was mediated by CD8 T cells. The maintenance of protective effector/memory CD8 T cells in CD4KO mice did not require the continuous presence of live BCG vaccine. As in C57BL/6 mice, similar levels of primary activation of CD8 T cells in CD4KO mice occurred in the draining lymph nodes at 3 wk after BCG vaccination, but different from C57BL/6 mice, the distribution of these cells to the spleen and lungs of CD4KO mice was delayed, which coincided with delayed acquisition of protection in CD4KO mice. Our results suggest that both the primary and secondary activation of CD8 T cells is CD4 T cell independent and that the maintenance of these CD8 T cells is also independent of CD4 T cells and no longer requires the presence of live mycobacteria. However, the lack of CD4 T cells may result in delayed distribution of activated CD8 T cells from draining lymph nodes to distant organs and consequently a delayed acquisition of immune protection. Our findings hold implications in rational design of tuberculosis vaccination strategies for humans with impaired CD4 T cell function.

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.

Response of IFN-gamma and IgG to ESAT-6 and 38 kDa recombinant proteins and their peptides from Mycobacterium tuberculosis in tuberculosis patients and asymptomatic household contacts may indicate possible early-stage infection in the latter

BACKGROUND

The ESAT-6 antigen from Mycobacterium tuberculosis evokes a protective immune response in murine models and is widely recognized by tuberculosis patients (TB) and healthy household contacts (HHC). However, little is known about human immune response to this antigen in populations from areas of high endemicity. This study aimed to determine the capacity of T-cells from a group of TB patients and HHC for cell proliferation and production of cytokines type Th1 or Th2 (IL-4, IL-10, and IFN-gamma) and to identify total IgG reactivity to the recombinant protein rESAT-6 and five overlapping synthetic peptides as well as to r38 kDa and two peptides.

METHODS

T-cells from nine TB patients and nine HHC were stimulated with rESAT-6 and five overlapping synthetic peptides, previously selected from a set of 21 peptides and each of 16 amino acids in length (P1, P4, P6, P8, and P20). Similar experiments were carried out with r38 kDa and two peptides of 20 amino acids in length (38G and 38K). Cytokines in supernatants and total IgG from serum were determined by ELISA.

RESULTS

Stimulation index (SI) was highest in HHC to rESAT-6 and peptides P1, P8, and P20. Differences in response to 38 kDa and 38G peptide between TB patients and HHC were not demonstrated. Cytokines from T-cell cultures were tested with a resulting SI=3.0. IFN-gamma was produced predominantly in HHC to rESAT-6, P8, and P20, while in TB patients production of IL-10 was detected in relation to r38 kDa. IL-4 was detected in minimal amounts in both groups. IgG from TB patients was predominantly recognized in connection with rESAT-6 and the P4 peptide, with an important response against r38 kDa detected in HHC.

CONCLUSIONS

ESAT-6 recognition by HHC could indicate that these responses represent possible early-stage infections.

Mycobacterium tuberculosis LprG (Rv1411c): a novel TLR-2 ligand that inhibits human macrophage class II MHC antigen processing

MHC class II (MHC-II)-restricted CD4(+) T cells are essential for control of Mycobacterium tuberculosis infection. This report describes the identification and purification of LprG (Rv1411c) as an inhibitor of primary human macrophage MHC-II Ag processing. LprG is a 24-kDa lipoprotein found in the M. tuberculosis cell wall. Prolonged exposure (>16 h) of human macrophages to LprG resulted in marked inhibition of MHC-II Ag processing. Inhibition of MHC-II Ag processing was dependent on TLR-2. Short-term exposure (<6 h) to LprG stimulated TLR-2-dependent TNF-alpha production. Thus, LprG can exploit TLR-2 signaling to inhibit MHC-II Ag processing in human macrophages. Inhibition of MHC-II Ag processing by mycobacterial lipoproteins may allow M. tuberculosis, within infected macrophages, to avoid recognition by CD4(+) T cells.

Identification of Mycobacterium tuberculosis counterimmune (cim) mutants in immunodeficient mice by differential screening

Tuberculosis (TB) is characterized by lifetime persistence of Mycobacterium tuberculosis. Despite the induction of a vigorous host immune response that curtails disease progression in the majority of cases, the organism is not eliminated. Subsequent immunosuppression can lead to reactivation after a prolonged period of clinical latency. Thus, while it is clear that protective immune mechanisms are engaged during M. tuberculosis infection, it also appears that the pathogen has evolved effective countermechanisms. Genetic studies with animal infection models and with patients have revealed a key role for the cytokine gamma interferon (IFN-gamma) in resistance to TB. IFN-gamma activates a large number of antimicrobial pathways. Three of these IFN-gamma-dependent mechanisms have been implicated in defense against M. tuberculosis: inducible nitric oxide synthase (iNOS), phagosome oxidase (phox), and the phagosome-associated GTPase LRG-47. In order to identify bacterial genes that provide protection against specific host immune pathways, we have developed the strategy of differential signature-tagged transposon mutagenesis. Using this approach we have identified three M. tuberculosis genes that are essential for progressive M. tuberculosis growth and rapid lethality in iNOS-deficient mice but not in IFN-gamma-deficient mice. We propose that these genes are involved in pathways that allow M. tuberculosis to counter IFN-gamma-dependent immune mechanisms other than iNOS.

Immunity to tuberculosis

Only 5 to 10% of immunocompetent humans are susceptible to tuberculosis, and over 85% of them develop the disease exclusively in the lungs. Human immunodeficiency virus (HIV)-infected humans, in contrast, can develop systemic disease that is more quickly lethal. This is in keeping with other evidence showing that susceptible humans generate some level of Th1 immunity to Mycobacterium tuberculosis (Mtb) infection. Tuberculosis in mice is also exclusively a lung disease that is progressive and lethal, in spite of the generation of Th1-mediated immunity. Thus mouse tuberculosis is a model of tuberculosis in susceptible humans, as is tuberculosis in guinea pigs and rabbits. Inability to resolve infection and prevent disease may not be a consequence of the generation of an inadequate number of Th1 cells but of an intrinsic deficiency in macrophage function that prevents these cells from expressing immunity. If this proves to be true, vaccinating susceptible humans against tuberculosis will be a difficult task.

Immunology of tuberculosis and implications in vaccine development

Mycobacterium tuberculosis is a very successful pathogen that can survive and persist in the human host in the face of a robust immune response. This immune response is sufficient to prevent disease in the majority of infected persons, providing compelling evidence that immunity to tuberculosis is possible. However, it is more striking that the strong immune response is not generally effective at eliminating the organisms, during either initial infection or the persistent or latent phase of infection. Studies in animal models and in humans have demonstrated the wide range of immune components involved in the effective response against M. tuberculosis. These components include T cells (both CD4+ and CD8+), cytokines, including IFN-gamma, IL-12, TNF-alpha, and IL-6, and macrophages. The precise roles and functions of these cells and molecules (and others) are still being defined and may differ in acute and chronic infection. These immune responses are directed towards containing or eliminating the tubercle bacillus within the tissues of the host. The estimated eight million new cases of tuberculosis each year clearly demonstrate that these responses are not always effective. M. tuberculosis has obviously evolved a variety of mechanisms to evade destruction by the immune response. Studying both the host and the pathogen will elucidate potential vaccine candidates. In this review, the known functions of immune components in the response to M. tuberculosis and implications for vaccine development will be discussed.

Effect of growth state on transcription levels of genes encoding major secreted antigens of Mycobacterium tuberculosis in the mouse lung

Arrest of the multiplication of Mycobacterium tuberculosis caused by expression of adaptive immunity in mouse lung was accompanied by a 10- to 20-fold decrease in levels of mRNAs encoding the secreted Ag85 complex and 38-kDa lipoprotein. esat-6 mRNA levels were high throughout infection. The data imply that multiplying and nonreplicating tubercle bacilli have different antigen compositions.

Alcohol exacerbates murine pulmonary tuberculosis

Alcohol consumption has been described as a risk factor for infection with Mycobacterium tuberculosis, but its contribution to tuberculosis has been difficult to isolate from other adverse socioeconomic factors. Our objective was to evaluate the impact of alcohol consumption on pulmonary infection with M. tuberculosis in a murine model. BALB/c mice were maintained on the Lieber-DeCarli liquid ethanol diet or a liquid control diet and infected intratracheally with low-dose M. tuberculosis H37Rv. Lung organism burdens, lung and lung-associated lymph node CD4(+)- and CD8(+)- lymphocyte numbers and rates of proliferation, and CD4(+)-lymphocyte cytokine production levels were compared between the groups. The alcohol-consuming mice had significantly higher lung organism burdens than the control mice, and the CD4(+)- and CD8(+)-lymphocyte responses to pulmonary infection with M. tuberculosis were blunted in the alcohol group. Lymphocyte proliferation and production of gamma interferon were decreased in the CD4(+) lymphocytes from the alcohol-consuming mice. Additionally, lung granulomas were significantly smaller in the alcohol-consuming mice. In conclusion, murine alcohol consumption is associated with decreased control of pulmonary infection with M. tuberculosis, which is accompanied by alterations in the region-specific CD4(+)- and CD8(+)-lymphocyte responses and defective lung granuloma formation.

Mice deficient in LRG-47 display increased susceptibility to mycobacterial infection associated with the induction of lymphopenia

Although IFN-gamma is essential for host control of mycobacterial infection, the mechanisms by which the cytokine restricts pathogen growth are only partially understood. LRG-47 is an IFN-inducible GTP-binding protein previously shown to be required for IFN-gamma-dependent host resistance to acute Listeria monocytogenes and Toxoplasma gondii infections. To examine the role of LRG-47 in control of mycobacterial infection, LRG-47(-/-) and wild-type mice were infected with Mycobacterium avium, and host responses were analyzed. LRG-47 protein was strongly induced in livers of infected wild-type animals in an IFN-gamma-dependent manner. LRG-47(-/-) mice were unable to control bacterial replication, but survived the acute phase, succumbing 11-16 wk postinfection. IFN-gamma-primed, bone marrow-derived macrophages from LRG-47(-/-) and wild-type animals produced equivalent levels of TNF and NO upon M. avium infection in vitro and developed similar intracellular bacterial loads. In addition, priming for IFN-gamma production was observed in T cells isolated from infected LRG-47(-/-) mice. Importantly, however, mycobacterial granulomas in LRG-47(-/-) mice showed a marked lymphocyte deficiency. Further examination of these animals revealed a profound systemic lymphopenia and anemia triggered by infection. As LRG47(-/-) T lymphocytes were found to both survive and confer resistance to M. avium in recipient recombinase-activating gene-2(-/-) mice, the defect in cellular response and bacterial control in LRG-47(-/-) mice may also depend on a factor(s) expressed in a nonlymphocyte compartment. These findings establish a role for LRG-47 in host control of mycobacteria and demonstrate that in the context of the IFN-gamma response to persistent infection, LRG-47 can have downstream regulatory effects on lymphocyte survival.

Immunization with a DNA vaccine cocktail protects mice lacking CD4 cells against an aerogenic infection with Mycobacterium tuberculosis

Tuberculosis (TB) is the most common opportunistic disease and a potentially fatal complication among immunocompromised individuals infected with human immunodeficiency virus (HIV). Effective vaccination against TB in persons with HIV has been considered unlikely because of the central role that CD4 cells play in controlling tuberculous infections. Here we show that the vaccination of CD8(-/-) mice with a TB DNA vaccine cocktail did not significantly enhance protective responses to a Mycobacterium tuberculosis infection. In contrast, immunization with a DNA vaccine cocktail or with the current TB vaccine, Mycobacterium bovis BCG, induced considerable antituberculosis protective immunity in immune-deficient mice lacking CD4 cells. In vaccinated CD4(-/-) animals, substantially reduced bacterial burdens in organs and much improved lung pathology were seen 1 month after an aerogenic M. tuberculosis challenge. Importantly, the postchallenge mean times to death of vaccinated CD4(-/-) mice were significantly extended (mean with DNA cocktail, 172 +/- 7 days; mean with BCG, 156 +/- 22 days) compared to that of naïve CD4(-/-) mice (33 +/- 6 days). Furthermore, the treatment of DNA-vaccinated CD4(-/-) mice with an anti-CD8 or anti-gamma interferon (IFN-gamma) antibody significantly reduced the effect of immunization, and neither IFN-gamma(-/-) nor tumor necrosis factor receptor-deficient mice were protected by DNA immunization; therefore, the primary vaccine-induced protective mechanism in these immune-deficient mice likely involves the secretion of cytokines from activated CD8 cells. The substantial CD8-mediated protective immunity that was generated in the absence of CD4 cells suggests that it may be possible to develop effective TB vaccines for use in HIV-infected populations.

Gammadelta T cells in immunity induced by Mycobacterium bovis bacillus Calmette-Guérin vaccination

Mycobacterium bovis bacillus Calmette-Guérin (BCG) vaccination is efficacious for newborns or adults with no previous exposure to environmental mycobacteria. To determine the relative contribution and the nature of gammadelta T-cell receptor-positive T cells in newborns, compared to CD4(+) T cells, in immunity induced by M. bovis BCG vaccination, 4-week-old specific-pathogen-free pigs were vaccinated with M. bovis BCG and monitored by following the gammadelta T-cell immune responses. A flow cytometry-based proliferation assay and intracellular staining for gamma interferon (IFN-gamma) were used to examine gammadelta T-cell responses. Pigs were found to mount Th1-like responses to M. bovis BCG vaccination as determined by immunoproliferation and IFN-gamma production. The gammadelta T-cell lymphoproliferation and IFN-gamma production to stimulation with mycobacterial antigens were significantly enhanced by M. bovis BCG vaccination. The relative number of proliferating gammadelta T cells after stimulating peripheral blood mononuclear cells with Mycobacterium tuberculosis H37Rv culture filtrate protein was higher than that of CD4(+) T cells at an early time point after M. bovis BCG vaccination, but CD4(+) T cells were found to be more abundant at a later time point. Although the gammadelta T-cell responses were dependent on the presence of CD4(+) T cells for the cytokine interleukin-2, the enhanced gammadelta T cells were due to the intrinsic changes of gammadelta T cells caused by M. bovis BCG vaccination rather than being due solely to help from CD4(+) T cells. Our study shows that gammadelta T cells from pigs at early ages are functionally enhanced by M. bovis BCG vaccination and suggests an important role for this T-cell subset in acquired immunity conferred by M. bovis BCG vaccination.

Innate inhibition of adaptive immunity: Mycobacterium tuberculosis-induced IL-6 inhibits macrophage responses to IFN-gamma

In humans and in mice, control of the intracellular pathogen, Mycobacterium tuberculosis (Mtb), requires IFN-gamma. Although the adaptive immune response results in production of substantial amounts of IFN-gamma in response to Mtb, the immune response is unable to eradicate the infection in most cases. We have previously reported evidence that Mtb inhibits macrophage responses to IFN-gamma, suggesting that this may limit the ability of IFN-gamma to stimulate macrophages to kill Mtb. We have also observed that uninfected macrophages, adjacent to infected macrophages in culture, exhibit decreased responses to IFN-gamma. Here we report that IL-6 secreted by Mtb-infected macrophages inhibits the responses of uninfected macrophages to IFN-gamma. IL-6 selectively inhibits a subset of IFN-gamma-responsive genes at the level of transcriptional activation without inhibiting activation or function of STAT1. Inhibition of macrophage responses to IFN-gamma by IL-6 requires new protein synthesis, but this effect is not attributable to suppressor of cytokine signaling 1 or 3. These results reveal a novel function for IL-6 and indicate that IL-6 secreted by Mtb-infected macrophages may contribute to the inability of the cellular immune response to eradicate infection.

CD40, but not CD40L, is required for the optimal priming of T cells and control of aerosol M. tuberculosis infection

CD40(-/-) mice succumbed to low-dose aerosol infection with M. tuberculosis due to deficient IL-12 production leading to impaired priming of IFN-gamma T cell responses. In contrast, CD40L(-/-) mice were resistant to M. tuberculosis. This asymmetry in outcome of infection between the two knockout strains is likely due to the existence of an alternative ligand for CD40. Both in vitro M. tuberculosis infection and recombinant M. tuberculosis Hsp70 elicited IL-12 production from WT dendritic cells. This response was absent in both CD40(-/-) dendritic cells and CD40(-/-) mice, suggesting that M. tuberculosis Hsp70 serves as an alternative ligand for CD40 in vivo.

Resistance and susceptibility to tuberculosis analysed at the transcriptome level: lessons from mouse macrophages

Gene expression patterns associated with resistance and susceptibility to tuberculosis (TB) were investigated at the macrophage level in the well-defined mouse model of infection. Oligonucleotide microarrays were used to analyse the regulation of gene expression in murine bone marrow-derived macrophages infected with Mycobacterium tuberculosis. Four mouse strains, known to differ in terms of growth permissiveness for M. tuberculosis in infected tissues, in the development of pulmonary pathology, and in the rate of premature death due to tuberculosis, were compared: C57BL/6 and BALB/c representing resistant, DBA/2 and CBA/J representing susceptible mouse strains. Genes (55) were regulated more than two-fold in macrophages of all strains investigated following M. tuberculosis infection. Importantly, 18 genes were commonly regulated only in macrophages of the two resistant strains upon infection, and 102 genes were commonly regulated exclusively in macrophages of the two susceptible strains. Using this approach, we have therefore identified more than 100 genes potentially associated with resistance and susceptibility, respectively, to TB at the macrophage level. A tentative interpretation of our microarray data suggests that macrophages from susceptible mice predominantly stimulate the recruitment of cells that contribute disproportionately to tissue damage rather than to microbial elimination. In conclusion, microarray gene chips are useful tools for generating new hypotheses about resistance and susceptibility to TB, and the mouse model can now be used to subject candidate genes identified by this approach to further functional analyses.

CD3 bright lymphocyte population reveal ?? T cells

BACKGROUND

In routine CD3/CD4/CD8 T-cell analysis, a CD3 bright population of lymphocytes is frequently observed. The aim of the present study was to identify the immunological significance of such CD3 bright lymphocytes.

METHODS

We analyzed samples from 31 healthy adult volunteers, 78 human immunodeficiency virus (HIV)-positive, and 78 renal transplanted patients.

RESULTS

A clearly distinct CD3 bright (frequently CD4-/CD8-) T-cell fraction was observed in 84% of donors and was directly correlated with the fraction of gammadelta T cells (r2 = 0.64). CD3 overexpression on gammadelta T cells was confirmed by a combination of monoclonal antibody staining (CD3-ECD, gammadeltaTCR-FITC, and alphabetaTCR-PE-Cy5) or immunomagnetic purification of gammadelta T cells (i.e., MdFI 20 vs 8.86). The gammadelta T cells expressed CD8 polypeptide chains (alpha and beta) in all possible combinations. The largest proportion, surprisingly, were cells expressing CD8betabeta homodimers (43.8 +/- 16.5%). CD8alphaalpha homodimers were expressed on 14.2% (+/- 12.3) of total gammadelta T cells, whereas CD8alphabeta heterodimers were expressed on 12.2% (+/- 7.5). We also observed a bimodal distribution of the intensity of CD3 fluorescence of gammadelta T cells in immunocompromised patients with a threshold at 105 cell/microl. CD3 bright gammadelta T cells were more frequently observed in HIV patients (29%) compared with renal transplant patients (11%) and healthy donors (3%; chi2 test: P = 0.0007).

CONCLUSIONS

The simple observation of a CD3 bright T-cell subset on CD3/CD4/CD8 routine analysis suggests a high gammadelta T-cell fraction and, in our opinion, should be followed by a complementary analysis to determine precisely the number of gammadelta T cells and to identify their CD8alpha/beta phenotype. When CD3 bright T cells/microl were more than 40%, high gammadelta T cells were detected in more than 87% of cases, with a specificity of 76%. Occasionally, the CD3 bright subset appeared to be strongly homogeneous, suggesting an oligoclonal proliferation that could possibly reveal a chronic localized stimulation or an early lymphoproliferative disorder. Because the gammadelta T cells have interesting immunological peculiarities, the clinical significance of their quantitative abnormality should be clarified in diseases such as HIV, organ transplantation, autoimmunity and lymphoma.

Mycobacterium tuberculosis-specific CD8+ T cells preferentially recognize heavily infected cells

Both CD4+ and CD8+ T cells are important for successful immunity to tuberculosis and have redundant effector functions, such as cytolysis and release of potent antimycobacterial cytokines such as interferon-gamma and tumor necrosis factor-alpha. We hypothesized that CD8+ T cells play a unique role in host defense to Mycobacterium tuberculosis infection as well. Possibilities include preferential and/or enhanced release of granular constituents and/or preferential recognition of heavily infected cells. Utilizing human, Mycobacterium tuberculosis-specific, CD4+ and CD8+ T cell clones, we demonstrate that, after recognition of antigen-presenting cells displaying peptide antigen, CD4+ T cells preferentially release interferon-gamma, whereas CD8+ T cells preferentially lyse antigen-presenting cells. Furthermore, utilizing dendritic cells infected with Mycobacterium tuberculosis expressing green fluorescent protein, we show that CD8+ T cells preferentially recognize heavily infected cells that constitute the minority of infected cells. These data support the hypothesis that the central role of CD8+ T cells in the control of infection with Mycobacterium tuberculosis may be that of surveillance; in essence, recognition of cells in which the containment of Mycobacterium tuberculosis is no longer effective.

Mycobacterium tuberculosis growth at the cavity surface: a microenvironment with failed immunity

Protective immunity against pulmonary tuberculosis (TB) is characterized by the formation in the lungs of granulomas consisting of macrophages and activated T cells producing tumor necrosis factor alpha and gamma interferon, both required for the activation of the phagocytes. In 90% of immunocompetent humans, this response controls the infection. To understand why immunity fails in the other 10%, we studied the lungs of six patients who underwent surgery for incurable TB. Histologic examination of different lung lesions revealed heterogeneous morphology and distribution of acid-fast bacilli; only at the surface of cavities, i.e., in granulomas with a patent connection to the airways, were there numerous bacilli. The mutation profile of the isolates suggested that a single founder strain of Mycobacterium tuberculosis may undergo genetic changes during treatment, leading to acquisition of additional drug resistance independently in discrete physical locales. Additional drug resistance was preferentially observed at the cavity surface. Cytokine gene expression revealed that failure to control the bacilli was not associated with a generalized suppression of cellular immunity, since cytokine mRNA was up regulated in all lesions tested. Rather, a selective absence of CD4(+) and CD8(+) T cells was noted at the luminal surface of the cavity, preventing direct T-cell-macrophage interactions at this site, probably allowing luminal phagocytes to remain permissive for bacillary growth. In contrast, in the perinecrotic zone of the granulomas, the two cell types colocalized and bacillary numbers were substantially lower, suggesting that in this microenvironment an efficient bacteriostatic or bactericidal phagocyte population was generated.

Widespread bronchogenic dissemination makes DBA/2 mice more susceptible than C57BL/6 mice to experimental aerosol infection with Mycobacterium tuberculosis

We have used the murine model of aerosol-induced experimental tuberculosis to assess the effects of four clinical isolates and a reference strain of Mycobacterium tuberculosis on resistant C57BL/6 mice and susceptible DBA/2 mice. Histological studies and detection of 25 cytokines potentially involved in the infection were carried out. DBA/2 mice showed higher concentrations of bacilli in bronchoalveolar lavage fluid and lung tissue. Furthermore, these mice evidenced a larger granulomatous infiltration in the parenchyma due to an increased rate of emigration of infected foamy macrophages from the granulomas to the neighboring pulmonary alveolar spaces. The better control of bacillary concentrations and pulmonary infiltration observed in C57BL/6 mice from week 3 postinfection could result from their higher RANTES, ICAM-1, and gamma interferon (IFN-gamma) mRNA levels. On the other hand, the higher MIP-2 and MCP-3 mRNA levels seen in DBA/2 mice would result in stronger lung recruitment of macrophages and neutrophils. Additionally, DBA/2 mice showed increased inducible nitric oxide synthase expression, induced by the larger number of foamy macrophages, at weeks 18 and 22. This increment was a consequence of phagocytosed bacillary debris, was independent of IFN-gamma expression, and could exert only a bacteriostatic effect. The results of the study suggest that DBA/2 mice are more susceptible than C57BL/6 mice to M. tuberculosis infection due to a higher bronchial dissemination of bacilli inside poorly activated foamy macrophages.

Control of Mycobacterium bovis BCG infection with increased inflammation in TLR4-deficient mice

Live mycobacteria have been reported to signal through several pattern recognition receptors (PRR), among them toll-like receptor 4 (TLR4) and TLR2 in vitro. Here, we investigated the role of TLR4 in host resistance to Mycobacterium bovis (BCG) infection in vivo. In vitro, macrophages of TLR4 mutant C3H/HeJ mice infected with BCG expressed lower levels of TNF than controls, and TNF release was further decreased, although not completely absent, in the absence of TLR2. In vivo, TLR4 mutant C3H/HeJ and control C3H/HeOUJ mice were infected with BCG (2 x 10(6) CFU i.v.). Both TLR4 mutant and wild-type mice were able to control the infection and survived 8 months post-BCG infection. Macrophage activation with abundant acid-fast bacilli and expression of inducible nitric oxide synthase (iNOS) and MHC class II antigens was seen in both groups of mice. However, TLR4 mutant mice experienced an arrest of body weight gain and showed signs of increased inflammation, with persistent splenomegaly, increase in granuloma number and augmented neutrophil infiltration. Infection of TLR4-deficient mice with higher doses of BCG (1 and 3 x 10(7) CFU, i.v.) increased the inflammation in spleen and liver, associated with a transient, higher bacterial load in the liver. In summary, TLR4 mutant mice show normal macrophage recruitment and activation, granuloma formation and control of the BCG infection, but this is associated with persistent inflammation. Therefore, TLR4 signaling is not essential for early control of BCG infection, but it may have a critical function in fine tuning of inflammation during chronic mycobacterial infection.

Latent tuberculosis: mechanisms of host and bacillus that contribute to persistent infection

Most people infected with Mycobacterium tuberculosis contain the initial infection and develop latent tuberculosis. This state is characterised by evidence of an immune response against the bacterium (a positive tuberculin skin test) but no signs of active infection. It can be maintained for the lifetime of the infected person. However, reactivation of latent infection occurs in about 10% of infected individuals, leading to active and contagious tuberculosis. An estimated 2 billion people worldwide are infected with M tuberculosis--an enormous reservoir of potential tuberculosis cases. The establishment and reactivation of latent infection depend on several factors, related to both host and bacterium. Elucidation of the host immune mechanisms that control the initial infection and prevent reactivation has begun. The bacillus is well adapted to the human host and has a range of evasion mechanisms that contribute to its ability to avoid elimination by the immune system and establish a persistent infection. We discuss here current understanding of both host and bacterial factors that contribute to latent and reactivation tuberculosis.

CD8 T cell responses to infectious pathogens

CD8 T cells respond to viral infections but also participate in defense against bacterial and protozoal infections. In the last few years, as new methods to accurately quantify and characterize pathogen-specific CD8 T cells have become available, our understanding of in vivo T cell responses has increased dramatically. Pathogen-specific T cells, once thought to be quite rare following infection, are now known to be present at very high frequencies, particularly in peripheral, nonlymphoid tissues. With the ability to visualize in vivo CD8 T cell responses has come the recognition that T cell expansion is programmed and, to a great extent, independent of antigen concentrations. Comparison of CD8 T cell responses to different pathogens also highlights the intricate relationship between microbially induced innate inflammatory responses and the kinetics, magnitude, and character of long-term T cell responses. This review describes recent progress in some of the major murine models of CD8 T cell-mediated immunity to viral, bacterial, and protozoal infection.

Alternate class I MHC antigen processing is inhibited by Toll-like receptor signaling pathogen-associated molecular patterns: Mycobacterium tuberculosis 19-kDa lipoprotein, CpG DNA, and lipopolysaccharide

Pathogen-associated molecular patterns (PAMPs) signal through Toll-like receptors (TLRs) to activate immune responses, but prolonged exposure to PAMPs from Mycobacterium tuberculosis (MTB) and other pathogens inhibits class II MHC (MHC-II) expression and Ag processing, which may allow MTB to evade CD4(+) T cell immunity. Alternate class I MHC (MHC-I) processing allows macrophages to present Ags from MTB and other bacteria to CD8(+) T cells, but the effect of PAMPs on this processing pathway is unknown. In our studies, MTB and TLR-signaling PAMPs, MTB 19-kDa lipoprotein, CpG DNA, and LPS, inhibited alternate MHC-I processing of latex-conjugated Ag by IFN-gamma-activated macrophages. Inhibition was dependent on TLR-2 for MTB 19-kDa lipoprotein (but not whole MTB or the other PAMPs); inhibition was dependent on myeloid differentiation factor 88 for MTB and all of the individual PAMPs. Inhibition of MHC-II and alternate MHC-I processing was delayed, appearing after 16 h of PAMP exposure, as would occur in chronically infected macrophages. Despite inhibition of alternate MHC-I Ag processing, there was no inhibition of MHC-I expression, MHC-I-restricted presentation of exogenous peptide or conventional MHC-I processing of cytosolic Ag. MTB 19-kDa lipoprotein and other PAMPs inhibited phagosome maturation and phagosome Ag degradation in a myeloid differentiation factor 88-dependent manner; this may limit availability of peptides to bind MHC-I. By inhibiting both MHC-II and alternate MHC-I Ag processing, pathogens that establish prolonged infection of macrophages (>16 h), e.g., MTB, may immunologically silence macrophages and evade surveillance by both CD4(+) and CD8(+) T cells, promoting chronic infection.

The Mycobacterium tuberculosis 19-kilodalton lipoprotein inhibits gamma interferon-regulated HLA-DR and Fc gamma R1 on human macrophages through Toll-like receptor 2

Mycobacterium tuberculosis survives in macrophages in the face of acquired CD4(+) T-cell immunity, which controls but does not eliminate the organism. Gamma interferon (IFN-gamma) has a central role in host defenses against M. tuberculosis by activating macrophages and regulating major histocompatibility complex class II (MHC-II) antigen (Ag) processing. M. tuberculosis interferes with IFN-gamma receptor (IFN-gamma R) signaling in macrophages, but the molecules responsible for this inhibition are poorly defined. This study determined that the 19-kDa lipoprotein from M. tuberculosis inhibits IFN-gamma-regulated HLA-DR protein and mRNA expression in human macrophages. Inhibition of HLA-DR expression was associated with decreased processing and presentation of soluble protein Ags and M. tuberculosis bacilli to MHC-II-restricted T cells. Inhibition of HLA-DR required prolonged exposure to 19-kDa lipoprotein and was blocked with a monoclonal antibody specific for Toll-like receptor 2 (TLR-2). The 19-kDa lipoprotein also inhibited IFN-gamma-induced expression of Fc gamma RI. Thus, M. tuberculosis, through 19-kDa lipoprotein activation of TLR-2, inhibits IFN-gamma R signaling in human macrophages, resulting in decreased MHC-II Ag processing and recognition by MHC-II-restricted CD4 T cells. These findings provide a mechanism for M. tuberculosis persistence in macrophages.

Immune biology of macaque lymphocyte populations during mycobacterial infection

Immune responses of lymphocyte populations during early phases of mycobacterial infection and reinfection have not been well characterized in humans. A non-human primate model of Mycobacterium bovis bacille Calmette-Guerin (BCG) infection was employed to characterize optimally the immune responses of mycobacteria-specific T cells. Primary BCG infection induced biphasic immune responses, characterized by initial lymphocytopenia and subsequent expansion of CD4+, CD8+ and gammadelta T cell populations in the blood, lymph nodes and the pulmonary compartment. The potency of detectable T cell immune responses appears to be influenced by the timing and route of infection as well as challenge doses of BCG organisms. Systemic BCG infection introduced by intravenous challenge induced a dose-dependent expansion of circulating CD4+, CD8+ and gammadelta T cells whereas, in the pulmonary compartment, the systemic infection resulted in a predominant increase in numbers of gammadelta T cells. In contrast, pulmonary exposure to BCG through the bronchial route induced detectable expansions of CD4+, CD8+ and gammadelta T cell populations in only the lung but not in the blood. A rapid recall expansion of these T cell populations was seen in the macaques reinfected intravenously and bronchially with BCG. The expanded alphabeta and gammadelta T cell populations exhibited their antigen specificity for mycobacterial peptides and non-peptide phospholigands, respectively. Finally, the major expansion of T cells was associated with a resolution of active BCG infection and reinfection. The patterns and kinetics of CD4+, CD8+ and gammadelta T cell immune responses during BCG infection might contribute to characterizing immune protection against tuberculosis and testing new tuberculosis vaccines in primates.

Role of chemokine ligand 2 in the protective response to early murine pulmonary tuberculosis

Chemokines play an important role in the development of immunity to tuberculosis. Chemokine ligand 2 (CCL2, JE, monocyte chemoattractant protein-1) is thought to be primarily responsible for recruiting monocytes, dendritic cells, natural killer cells and activated T cells, all of which play critical roles in the effective control of tuberculosis infection in mice. We show here that in mice in which the CCL2 gene was disrupted, low-dose aerosol infection with Mycobacterium tuberculosis resulted in fewer macrophages entering the lungs, but only a minor and transient increase in bacterial load in the lungs; these mice were still able to establish a state of chronic disease. Such animals showed similar numbers of activated T cells as wild-type mice, as determined by their expression of the CD44hi CD62lo phenotype, but a transient reduction in cells secreting interferon-gamma. These data indicate that the primary deficiency in mice unable to produce CCL2 is a transient failure to focus antigen-specific T lymphocytes into the infected lung, whereas other elements of the acquired host response are compensated for by different ligands interacting with the chemokine receptor CCR2.

Increased interleukin-10 expression is not responsible for failure of T helper 1 immunity to resolve airborne Mycobacterium tuberculosis infection in mice

With a view to determining whether failure of mice to resolve Mycobacterium tuberculosis (Mtb) infection is a consequence of downregulation of T helper 1 (Th1) immunity by interleukin (IL)-10, mice deleted of the gene for IL-10 were compared with wild-type (WT) mice in terms of their ability to make IL-10 mRNA, generate Th1-mediated immunity [as measured by synthesis of mRNA for interferon-gamma (IFN-gamma)], IL-12p40 and inducible nitric oxide synthase (iNOS), and to control lung infection. It was found that the response of WT mice to infection included a substantial and sustained increase in IL-10 mRNA synthesis in the lungs. A Th1 response in the lungs of WT and IL-10-/- mice was evidenced by a large and sustained increase in the synthesis of mRNA for IFN-gamma, IL-12p40 and iNOS, with somewhat higher levels of these mRNA species being made in the lungs of IL-10-/- mice, particularly at an early stage of infection. However, IL-10-/- mice were no more capable than WT mice at combating infection.

Susceptibility to tuberculosis: a locus on mouse chromosome 19 (Trl-4) regulates Mycobacterium tuberculosis replication in the lungs

The mouse DBA/2 (D2) strain is very susceptible to infection with virulent Mycobacterium tuberculosis, whereas C57BL/6 (B6) is much more resistant. Infection of D2 and B6 mice with M. tuberculosis H37Rv by the respiratory route is biphasic: during the first 3 weeks, there is rapid bacterial growth in the lung of both strains, whereas beyond this point replication stops in B6 but continues in D2, causing rapidly fatal pulmonary disease. To identify the genes regulating growth of M. tuberculosis in the lungs of these two strains, 98 informative (B6 x D2) F2 mice were infected by the respiratory route with M. tuberculosis H37Rv (2 x 102 colony-forming units), and the extent of bacterial replication in the lungs at 90 days was used as a quantitative measure of susceptibility in a whole-genome scan. Quantitative trait locus mapping identified a major locus on chromosome 19 (Tuberculosis resistance locus-4, Trl-4; logarithm of odds 5.6), which regulated pulmonary replication of M. tuberculosis and accounted for 25% of the phenotypic variance. B6 alleles at Trl-4 were inherited in an incompletely dominant fashion and associated with reduced bacterial replication. An additional effect of a locus (Trl-3), previously shown to affect survival to i.v. infection with M. tuberculosis, was also noted. F2 mice homozygous for B6 alleles at both Trl-3 and Trl-4 were as resistant as B6 parents, whereas mice homozygous for D2 alleles were as susceptible as D2 parents. These results suggest a strong genetic interaction between Trl-3 and Trl-4 in regulating pulmonary replication of M. tuberculosis.

The lymphotoxin beta receptor is critically involved in controlling infections with the intracellular pathogens Mycobacterium tuberculosis and Listeria monocytogenes

Containment of intracellularly viable microorganisms requires an intricate cooperation between macrophages and T cells, the most potent mediators known to date being IFN-gamma and TNF. To identify novel mechanisms involved in combating intracellular infections, experiments were performed in mice with selective defects in the lymphotoxin (LT)/LT beta R pathway. When mice deficient in LT alpha or LT beta were challenged intranasally with Mycobacterium tuberculosis, they showed a significant increase in bacterial loads in lungs and livers compared with wild-type mice, suggesting a role for LT alpha beta heterotrimers in resistance to infection. Indeed, mice deficient in the receptor for LT alpha(1)beta(2) heterotrimers (LT beta R-knockout (KO) mice) also had significantly higher numbers of M. tuberculosis in infected lungs and exhibited widespread pulmonary necrosis already by day 35 after intranasal infection. Furthermore, LT beta R-KO mice were dramatically more susceptible than wild-type mice to i.p. infection with Listeria monocytogenes. Compared with wild-type mice, LT beta R-KO mice had similar transcript levels of TNF and IFN-gamma and recruited similar numbers of CD3(+) T cells inside granulomatous lesions in M. tuberculosis-infected lungs. Flow cytometry revealed that the LT beta R is expressed on pulmonary macrophages obtained after digestion of M. tuberculosis-infected lungs. LT beta R-KO mice showed delayed expression of inducible NO synthase protein in granuloma macrophages, implicating deficient macrophage activation as the most likely cause for enhanced susceptibility of these mice to intracellular infections. Since LIGHT-KO mice proved to be equally resistant to M. tuberculosis infection as wild-type mice, these data demonstrate that signaling of LT alpha(1)beta(2) heterotrimers via the LT beta R is an essential prerequisite for containment of intracellular pathogens.

CD40 ligand trimer enhances the response of CD8+ T cells to Mycobacterium tuberculosis

We investigated the effect of recombinant CD40 ligand trimer (CD40LT) on the functional capacity of peripheral blood CD8(+) T cells from healthy tuberculin reactors that were cultured with Mycobacterium tuberculosis-infected autologous monocytes. CD40LT enhanced the capacity of M. tuberculosis-responsive CD8(+) T cells to produce IFN-gamma by increasing the number of IFN-gamma-producing CD8(+) T cells and the amount of IFN-gamma produced per cell. CD40LT-induced IFN-gamma production was dependent on production of IL-12 and IL-18, but did not require IL-15. CD40LT up-regulated expression of the transcription factors phosphorylated CREB and c-Jun, both of which have been previously shown to stimulate IFN-gamma mRNA transcription by binding to the IFN-gamma promoter. CD40LT also enhanced the capacity of CD8(+) T cells to lyse M. tuberculosis-infected monocytes, and increased CTL activity was associated with higher expression of perforin and granulysin, but not of Fas ligand. We conclude that CD40LT can enhance CD8(+) T cell effector function in response to M. tuberculosis.

Macrophages exposed to Mycobacterium tuberculosis release chemokines able to recruit selected leucocyte subpopulations: focus on gammadelta cells

Granuloma is a typical feature of tuberculosis. We evaluated the chemotaxis of selected human leucocyte subsets induced by macrophages incubated with Mycobacterium tuberculosis (MT)-derived products in vitro. The release of monocyte chemotactic protein 1 (MCP-1) and interleukin-8 (IL-8) correlated with the specific induction of strong chemotaxis towards monocytes and polymorphonuclear leucocytes (PMNs). gammadelta and T helper type 1 (Th1) alphabeta lymphocytes were chemoattracted, while T-resting, IL-2-activated and Th2 lymphocytes were unaffected. Activation with mycobacterium-derived, phosphate-containing components, modulated the chemokine receptor profile of gammadelta T lymphocytes as well as their pattern of cyto-chemokine production, disclosing a potential for their active participation in granuloma formation. In particular, CXCR3 and IP-10, which we found to be released by MT-pulsed alveolar macrophages, seem to represent the receptor-counter-receptor pair implicated in the chemotaxis of gammadelta lymphocytes. Immunohistochemical analysis and in situ hybridization revealed the in vivo presence of IL-8, MCP-1 and IL-10 in lymph node and lung tuberculous granulomas. Our results underscore the role of MT extracts in the induction of macrophage-derived chemokines responsible for the orchestrated recruitment of PMNs, monocytes, and Th1 and gammadelta T cells, as well as in the regulation of gammadelta function.

CD8+ T cells accumulate in the lungs of Mycobacterium tuberculosis-infected Kb-/-Db-/- mice, but provide minimal protection

Recent studies have shown that MHC class I molecules play an important role in the protective immune response to Mycobacterium tuberculosis infection. Here we showed that mice deficient in MHC class Ia, but possessing MHC class Ib (K(b-/-)D(b-/-) mice), were more susceptible to aerosol infection with M. tuberculosis than control mice, but less susceptible than mice that lack both MHC class Ia and Ib (beta(2)m(-/-) mice). The susceptibility of K(b-/-)D(b-/-) mice cannot be explained by the failure of CD8(+) T cells (presumably MHC class Ib-restricted) to respond to the infection. Although CD8(+) T cells were a relatively small population in uninfected K(b-/-)D(b-/-) mice, most already expressed an activated phenotype. During infection, a large percentage of these cells further changed their cell surface phenotype, accumulated in the lungs at the site of infection, and were capable of rapidly producing IFN-gamma following TCR stimulation. Histopathologic analysis showed widespread inflammation in the lungs of K(b-/-)D(b-/-) mice, with a paucity of lymphocytic aggregates within poorly organized areas of granulomatous inflammation. A similar pattern of granuloma formation has previously been observed in other types of MHC class I-deficient mice, but not CD8alpha(-/-) mice. Thus, neither the presence of MHC class Ib molecules themselves, nor the activity of a population of nonclassical CD8(+) effector cells, fully restored the deficit caused by the absence of MHC class Ia molecules, suggesting a unique role for MHC class Ia molecules in protective immunity against M. tuberculosis.

Persistence and turnover of antigen-specific CD4 T cells during chronic tuberculosis infection in the mouse

CD4 T cells are critical for resistance to Mycobacterium tuberculosis infection, but how effective T cell responses are maintained during chronic infection is not well understood. To address this question we examined the CD4 T cell response to a peptide from ESAT-6 during tuberculosis infection in the mouse. The ESAT-6(1-20)/IA(b)-specific CD4 T cell response in the lungs, mediastinal lymph nodes, and spleen reached maxima 3-4 wk postinfection, when the bacteria came under the control of the immune response. Once chronic infection was established, the relative frequencies of Ag-specific CD4 T cells were maintained at nearly constant levels for at least 160 days. ESAT-6(1-20)/IA(b)-specific CD4 T cells that responded in vitro expressed activation markers characteristic of chronically activated effector cells and used a limited Vbeta repertoire that was clonally stable in vivo for at least 12 wk. 5-Bromo-2-deoxyuridine incorporation studies indicated a relatively high rate of cell division among both total CD4 and ESAT-6(1-20)/IA(b)-specific CD4 T cells during acute infection, but the degree of 5-bromo-2-deoxyuridine incorporation by both the CD4 T cells and the Ag-specific cells declined at least 3-fold during chronic infection. The data indicate that the peripheral ESAT-6(1-20)/IA(b)-specific CD4 T cell response to M. tuberculosis is characterized during the acute phase of infection by a period of extensive proliferation, but once bacterial control is achieved, this is followed during chronic infection by an extended containment phase that is associated with a persistent response of activated, yet more slowly proliferating, T cells.

Mechanisms of cell recruitment in the immune response to Mycobacterium tuberculosis

Recent advances in understanding cell traffic, especially the roles of adhesion proteins, chemokines, and chemokine receptors, provide the opportunity for understanding mechanisms involved in the immune response to tuberculosis. This review concentrates on the roles of these molecules and the immune response in tuberculosis, based on studies of humans and mice infected with Mycobacterium tuberculosis.

Expression of Th1-mediated immunity in mouse lungs induces a Mycobacterium tuberculosis transcription pattern characteristic of nonreplicating persistence

The lung is the primary target of infection with Mycobacterium tuberculosis. It is well established that, in mouse lung, expression of adaptive, Th1-mediated host immunity inhibits further multiplication of M. tuberculosis. Here, real-time RT-PCR was used to define the pattern of expression against time of lung infection of key genes involved in Th1-mediated immunity and of selected genes of M. tuberculosis. Inhibition of bacterial multiplication was preceded by increased mRNA synthesis for IFN-gamma and inducible NO synthase (NOS2) and by NOS2 protein synthesis in infected macrophages. Concurrently, the pattern of transcription of bacterial genes underwent dramatic changes. mRNA synthesis increased for alpha-crystallin (acr), rv2626c, and rv2623 and decreased for superoxide dismutase C (sodC), sodA, and fibronectin-binding protein B (fbpB). This pattern of M. tuberculosis transcription is characteristic of the nonreplicating persistence [Wayne, L. G. & Sohaskey, C. D. (2001) Annu. Rev. Microbiol. 55, 139-163] associated with adaptation of tubercle bacilli to hypoxia in vitro. Based on this similarity, we infer that host immunity induces bacterial growth arrest. In IFN-gamma gene-deleted mice, bacterial growth was not controlled; NOS2 protein was not detected in macrophages; sodC, sodA, and fbpB transcription showed no decrease; and acr, rv2626c, and rv2623 transcription increased only at the terminal stages of lung pathology. These findings define the transcription signature of M. tuberculosis as it transitions from growth to persistence in the mouse lung. The bacterial transcription changes measured at onset of Th1-mediated immunity are likely induced, directly or indirectly, by nitric oxide generated by infected macrophages.