An ex vivo study of T lymphocytes recovered from the lungs of I/St mice infected with and susceptible to Mycobacterium tuberculosis

A new model for chronic and reactivation tuberculosis: Infection with genetically attenuated Mycobacterium tuberculosis in mice with polar susceptibility

TB infection in mice develops relatively rapidly which interferes with experimental dissection of immune responses and lung pathology features that differ between genetically susceptible and resistant hosts. Earlier we have shown that the M. tuberculosis strain lacking four of five Rpf genes (ΔACDE) is seriously attenuated for growth in vivo. Using this strain, we assessed key parameters of lung pathology, immune and inflammatory responses in chronic and reactivation TB infections in highly susceptible I/St and more resistant B6 mice. ΔACDE mycobacteria progressively multiplied only in I/St lungs, whilst in B6 lung CFU counts decreased with time. Condensed TB foci apeared in B6 lungs at week 4 of infection, whilst in I/St their formation was delayed. At the late phase of infection, in I/St lungs TB foci fused resulting in extensive pneumonia, whereas in B6 lungs pathology was limited to condensed foci. Macrophage and neutrophil populations characteristically differed between I/St and B6 mice at early and late stages of infection: more neutrophils accumulated in I/St and more macrophages in B6 lungs. The expression level of chemokine genes involved in neutrophil influx was higher in I/St compared to B6 lungs. B6 lung cells produced more IFN-γ, IL-6 and IL-11 at the early and late phases of infection. Overall, using a new mouse model of slow TB progression, we demonstrate two important features of ineffective infection control underlined by shifts in lung inflammation: delay in early granuloma formation and fusion of granulomas resulting in consolidated pneumonia late in the infectious course.

The introduction of mesenchymal stromal cells induces different immunological responses in the lungs of healthy and M. tuberculosis infected mice

Mesenchymal stromal cells (MSC) have strong immunomodulatory properties and therefore can be used to control inflammation and tissue damage. It was suggested recently that MSC injections can be used to treat multi-drug resistant tuberculosis (TB). However, MSC trafficking and immunomodulatory effects of MSC injections during Mycobacterium tuberculosis (Mtb) infection have not been studied. To address this issue we have analyzed MSC distribution in tissues and local immunological effects of MSC injections in Mtb infected and uninfected mice. After intravenous injection, MSC accumulated preferentially in the lungs where they were located as cell aggregates in the alveolar walls. Immunological analysis of MSC effects included detection of activated, IFN-γ and IL-4 producing CD4⁺ lymphocytes, the frequency analysis of dendritic cells (CD11c⁺F4/80) and macrophages (CD11c^-F4/80⁺) located in the lungs, the expression of IA/IE and CD11b molecules by these cells, and evaluation of 23 cytokines/chemokines in lung lysates. In the lungs of uninfected mice, MSC transfer markedly increased the percentage of IFN-γ⁺ CD4⁺ lymphocytes and dendritic cells, elevated levels of IA/IE expression by dendritic cells and macrophages, augmented local production of type 2 cytokines (IL-4, IL-5, IL-10) and chemokines (CCL2, CCL3, CCL4, CCL5, CXCL1), and downregulated type 1 and hematopoietic cytokines (IL-12p70, IFN-γ, IL-3, IL-6, GM-CSF). Compared to uninfected mice, Mtb infected mice had statistically higher “background” frequency of activated CD69⁺ and IFN-γ⁺ CD4⁺ lymphocytes and dendritic cells, and higher levels of cytokines in the lungs. The injections of MSC to Mtb infected mice did not show statistically significant effects on CD4⁺ lymphocytes, dendritic cells and macrophages, only slightly shifted cytokine profile, and did not change pathogen load or slow down TB progression. Lung section analysis showed that in Mtb infected mice, MSC could not be found in the proximity of the inflammatory foci. Thus, in healthy recipients, MSC administration dramatically changed T-cell function and cytokine/chemokine milieu in the lungs, most likely, due to capillary blockade. But, during Mtb infection, i.e., in the highly-inflammatory conditions, MSC did not affect T-cell function and the level of inflammation. The findings emphasize the importance of the evaluation of MSC effects locally at the site of their predominant post-injection localization and question MSC usefulness as anti-TB treatment.

Senescent cells expose and secrete an oxidized form of membrane-bound vimentin as revealed by a natural polyreactive antibody

Studying the phenomenon of cellular senescence has been hindered by the lack of senescence-specific markers. As such, detection of proteins informally associated with senescence accompanies the use of senescence-associated β-galactosidase as a collection of semiselective markers to monitor the presence of senescent cells. To identify novel biomarkers of senescence, we immunized BALB/c mice with senescent mouse lung fibroblasts and screened for antibodies that recognized senescence-associated cell-surface antigens by FACS analysis and a newly developed cell-based ELISA. The majority of antibodies that we isolated, cloned, and sequenced belonged to the IgM isotype of the innate immune system. In-depth characterization of one of these monoclonal, polyreactive natural antibodies, the IgM clone 9H4, revealed its ability to recognize the intermediate filament vimentin. By using 9H4, we observed that senescent primary human fibroblasts express vimentin on their cell surface, and MS analysis revealed a posttranslational modification on cysteine 328 (C328) by the oxidative adduct malondialdehyde (MDA). Moreover, elevated levels of secreted MDA-modified vimentin were detected in the plasma of aged senescence-accelerated mouse prone 8 mice, which are known to have deregulated reactive oxygen species metabolism and accelerated aging. Based on these findings, we hypothesize that humoral innate immunity may recognize senescent cells by the presence of membrane-bound MDA-vimentin, presumably as part of a senescence eradication mechanism that may become impaired with age and result in senescent cell accumulation.

Analysis of the lung transcriptome in Mycobacterium tuberculosis-infected mice reveals major differences in immune response pathways between TB-susceptible and resistant hosts

Using whole genome microarrays, we compared changes in gene expression patterns in the lungs of TB-resistant A/Sn and TB-susceptible I/St mice at day 14 following infection with Mycobacterium tuberculosis H37Rv. Analyses of differentially expressed genes for representation of gene ontology terms and activation of regulatory pathways revealed interstrain differences in antigen presentation, NK, T and B cell activation pathways. In general, resistant A/Sn mice exhibited a more complex pattern and stronger activation of host defense pathways compared to the TB-susceptible I/St mouse strain. In addition, in I/St mice elevated activation of genes involved in neutrophil response was observed and confirmed by quantitative RT-PCR and histopathology. Furthermore, a specific post infection upregulation of cysteine protease inhibitors was found in susceptible I/St mice.

Peripheral blood gamma interferon release assays predict lung responses and Mycobacterium tuberculosis disease outcome in mice

Current diagnostic tests for tuberculosis (TB) are not able to distinguish active disease from latent Mycobacterium tuberculosis infection, nor are they able to quantify the risk of a latently infected person progressing to active TB. There is interest, however, in adapting antigen-specific gamma interferon (IFN-gamma) release assays (IGRAs) to predict disease outcome. In this study, we used the differential susceptibilities of inbred mouse strains to M. tuberculosis infection to evaluate the prognostic capabilities of IGRAs. Using lung and blood cultures, we determined that CBA/J, DBA/2, and C3H/HeJ mice (models of heightened risk of progression to active TB) produced less antigen-specific IFN-gamma in response to M. tuberculosis culture filtrate proteins and early secreted antigenic target-6 than the relatively resistant C57BL/6 mouse strain. Additionally, reduced IFN-gamma secretion in supernatants reflected a reduced frequency of IFN-gamma-responding cells in the lung and blood and not a specific defect in IFN-gamma secretion at the single-cell level. Importantly, detection of antigen-specific IFN-gamma from blood cultures accurately reflected lung responses, indicating that blood can be an appropriate test tissue in humans. Furthermore, reduced antigen-specific IFN-gamma production and low frequencies of IFN-gamma-responding cells from peripheral blood predicted increased risk of TB disease progression across genetically diverse TB disease-susceptible mouse strains, suggesting that similar results may occur in humans. The development of efficacious predictive diagnostic tests for humans would lead to targeted therapy prior to progression to active TB, reducing transmission, incidence, and prevalence rates while maximizing the use of public health resources.

Specificity and efficacy of dendritic cell-based vaccination against tuberculosis with complex mycobacterial antigens in a mouse model

Dendritic cells (DC) likely play important and unique roles in the generation of protective immunity to mycobacteria. In order to clarify their contributions, bone marrow-derived DC loaded with Mycobacterium tuberculosis sonicate antigens were used to stimulate T cell proliferation both in vitro and in vivo and to vaccinate C57BL/6 mice against subsequent challenge with virulent mycobacteria. Antigen-pulsed DC developed in fetal calf serum (FCS-DC), but not DC developed in normal mouse serum (NMS-DC), stimulated significant proliferation of both naïve and immune T cells in vitro. The difference between cell populations developed in FCS and NMS in the content of CD11c(+) cells and in production of key cytokines indicated that NMS is less supportive for the development of activated DC. However, following adoptive transfer of a single dose of antigen-pulsed DC into naive recipients, NMS-DC induced T cells that proliferated in response to mycobacterial antigen, whereas FCS-DC stimulated strong non-specific proliferation. Vaccination with two doses of antigen-pulsed NMS-DC by the subcutaneous route induced significant protection against intravenous challenge with a moderate dose of virulent M. tuberculosis. DC-vaccinated mice exhibited significant reductions in bacillary loads in the lungs and spleens, and markedly reduced lung pathology. Three doses of antigen-pulsed NMS-DC induced a significant increase in survival time following high dose challenge, which correlated with a significant increase in IFN-gamma-producing cells in both lung and lymphoid tissues, as assessed by the ELISPOT assay. Taken together, these results indicate that DC play a critical role in the induction of protective resistance against virulent mycobacterial challenge accompanied by the development of antigen-reactive, IFN-gamma-producing T cells, and that their antigenic specificity is influenced by the culture conditions under which the DC are developed.

Morphine modulates gammadelta lymphocytes cytolytic activity following BCG vaccination

Chronic opioid administration modulates lymphocytes' functional capabilities increasing susceptibility to infectious diseases. Bacille-Calmette-Guérin (BCG) vaccination initiates a non-specific and specific cell-mediated immunity orchestrated by T lymphocytes including gammadelta T lymphocytes. gammadelta T lymphocytes increase in natural killer and antigen-directed cytolytic response following BCG vaccination. The objective of this study was to determine morphine effects on gammadelta T lymphocytes' cytolytic activity. Pigs were chronically administered morphine and subsequently vaccinated with Mycobacterium bovis BCG. By administering morphine prior to BCG vaccination, natural killer response was significantly suppressed (p=.034). Furthermore, innate cytolytic response against M. bovis-infected monocytes (p=.002) as well as antigen specific cytolytic functions (p=.04) were significantly altered due to morphine administration. It was concluded that administering morphine prior to BCG vaccination significantly altered gammadelta T lymphocyte cytolytic responses.

Antigen-specific proliferation and activation of peripheral blood mononuclear cells from Mycobacterium bovis-infected reindeer

To evaluate antigen-specific proliferative and activation-associated responses from Mycobacterium bovis-infected reindeer, blood mononuclear cells from M. bovis- (n = 10) and non-infected reindeer (n = 4) were stimulated with a recombinant early secretory antigenic target-6 and culture filtrate protein-10 fusion protein (rESAT6:CFP10), M. bovis purified protein derivative, pokeweed mitogen, or medium alone and evaluated by flow cytometry using dye tracker analysis and cell surface marker staining. gammadelta TCR+ and CD8+ cells, but not CD4+ cells, from M. bovis-infected reindeer proliferated in response to specific antigen stimulation. Expression (i.e., mean fluorescence intensity) of CD44 was increased and CD62L decreased on proliferative as compared to non-proliferative fractions in antigen- and mitogen-stimulated cultures. In response rESAT6:CFP10 stimulation, MHC II fluorescence intensity was increased on CD4+, gammadelta TCR+, CD172a+, and IgM+ cells from infected reindeer as compared to that of non-stimulated cells from the same reindeer. Recombinant ESAT6:CFP10 stimulation also induced expansion of a CD172a+, MHC II+ population within mononuclear cell cultures from M. bovis-infected reindeer. Despite a moderate challenge dose and extended duration of incubation, experimental infection of reindeer was generally limited to lymph nodes draining the inoculation site, suggestive of host resistance to progressive disease. Present in vitro findings, therefore, may be predictive of host responses by reindeer that limit progression to disseminated disease.

The OtsAB pathway is essential for trehalose biosynthesis in Mycobacterium tuberculosis

The disaccharide trehalose is the major free sugar in the cytoplasm of mycobacteria; it is a constituent of cell wall glycolipids, and it plays a role in mycolic acid transport during cell wall biogenesis. The pleiotropic role of trehalose in the biology of Mycobacterium tuberculosis and its absence from mammalian cells suggests that its biosynthesis may provide a useful target for novel drugs. However, there are three potential pathways for trehalose biosynthesis in M. tuberculosis, and the aim of the present study was to introduce mutations into each of the pathways to determine whether or not they are functionally redundant. The results show that the OtsAB pathway, which generates trehalose from glucose and glucose-6-phosphate, is the dominant pathway required for M. tuberculosis growth in laboratory culture and for virulence in a mouse model. Of the two otsB homologues annotated in the genome sequence of M. tuberculosis, only OtsB2 (Rv3372) has a functional role in the pathway. OtsB2, trehalose-6-phosphate phosphatase, is strictly essential for growth and provides a tractable target for high throughput screening. Inactivation of the TreYZ pathway, which can generate trehalose from alpha-1,4-linked glucose polymers, had no effect on the growth of M. tuberculosis in vitro or in mice. Deletion of the treS gene altered the late stages of pathogenesis of M. tuberculosis in mice, significantly increasing the time to death in a chronic infection model. Because the TreS enzyme catalyzes the interconversion of trehalose and maltose, the mouse phenotype could reflect either a requirement for synthesis of additional trehalose or, conversely, a requirement for breakdown of stored trehalose to liberate free glucose.

Direct comparison of low-dose and Cornell-like models of chronic and reactivation tuberculosis in genetically susceptible I/St and resistant B6 mice

We applied the low-dose challenge (chronic) and reactivation following chemotherapy withdrawal (Cornell-like) TB models to mouse strains with genetically different susceptibility to and severity of Mycobacterium tuberculosis-triggered disease. Systemic infection caused by intravenous (i.v.) administration of approximately 70 cfus of M. tuberculosis H37Rv lead to chronic, persistent, non-lethal disease in genetically resistant B6 mice, but resulted in a fatal pathological process in the lungs of susceptible I/St animals. Thus, application of the identical experimental approach to genetically different murine hosts allows investigating both slowly progressive disease with the fatal outcome (I/St) and chronic life-span disease (B6). Under Cornell-like model conditions, both temporary eradication of cultivable bacilli from lungs and spleens due to chemotherapy and their re-appearance in organs following its withdrawal were demonstrated in mice of both strains. However, (i) reactivation occurred significantly earlier in I/St than in B6 mice; (ii) I/St mice survived not more than 6 month following chemotherapy withdrawal and demonstrated 100% TB relapse, whereas in B6 mice mortality did not exceed 50%, and no mycobacteria were recovered from some animals. I/St mice, with their genetically determined high TB severity, provide a more reliable tool for modeling TB relapse after chemotherapy withdrawal than mice of more resistant strains.

Abnormal production of transforming growth factor beta and interferon gamma by peripheral blood cells of patients with multidrug-resistant pulmonary tuberculosis in Brazil

OBJECTIVES

The aim of the present study was to determine the immune response profile that differentiates patients with newly diagnosed (non-treated) pulmonary tuberculosis from multidrug-resistant (MDR) ones, as well as from healthy, tuberculin positive individuals.

METHODS

Lymphocytes proliferative response to non-specific mitogen (PHA) and PPD were evaluated by 3H thymidine incorporation and cytokines were quantified using an ELISA assay.

RESULTS

Patients with active disease showed a diminished proliferative response to PHA and PPD, while multidrug-resistant patients showed a diminished proliferative response to PHA, but a normal response to PPD. The cytokine production of newly diagnosed patients was characterized by a diminished production of IFNgamma and normal production of transforming growth factor (TGFbeta), while MDR patients revealed a normal production of IFNgamma accompanied by an increase in TGFbeta.

CONCLUSIONS

The production of significant amounts of TGFbeta in MDR patients leads to a poor immune response and may contribute to the resistance of tuberculosis patients to drugs.

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.

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.

Lung cell responses to M. tuberculosis in genetically susceptible and resistant mice following intratracheal challenge

One approach to study the role of distinct cellular mechanisms in susceptibility/resistance to tuberculosis (TB) is to compare parameters of response to infection in the lungs of mouse strains exhibiting genetically determined differences in TB susceptibility/severity. Interstrain differences in antimycobacterial macrophage reactions, T cell responses & inflammation in the lungs of TB-susceptible I/St, TB-resistant A/Sn and (I/St x A/Sn)F1 mice were analysed following intratracheal inoculation of 103 CFUs of M. tuberculosis H37Rv. The antimycobacterial responses in the lungs of susceptible I/St mice were characterized by: (i) increased inflammatory infiltration by all major immune cell subsets; (ii) decreased type 1 cytokine production; (iii) impaired antimycobacterial activity of lung macrophages; (iv) unusually high proliferation of lung T lymphocytes. Differences in several parameters of anti-TB immunity between susceptible and resistant mice corresponded well to the polygenic pattern of TB control previously established in this mouse model. Importantly, lung macrophages isolated from noninfected mice were unable to respond to IFN-gamma by increasing their mycobactericidal function, but between weeks 3 and 5 of the infection this capacity developed in all mice. However, by this time point susceptible but not resistant mice demonstrated a pronounced decrease in IFN-gamma production by lung cells. This chain of events may explain the inability of I/St mice to control both early and chronic TB infection.

Proteins of the Rpf family: immune cell reactivity and vaccination efficacy against tuberculosis in mice

It was shown recently that Mycobacterium tuberculosis expresses five proteins that are homologous to Rpf (resuscitation promoting factor), which is secreted by growing cells of Micrococcus luteus. Rpf is required to resuscitate the growth of dormant Micrococcus luteus organisms, and its homologues may be involved in mycobacterial reactivation. Mycobacterial Rpf-like products are secreted proteins, which makes them candidates for recognition by the host immune system and anti-Rpf immune responses potentially protective against reactivated tuberculosis. Here we report that the Rpf protein itself and four out of five of its mycobacterial homologues, which were administered as subunit vaccines to C57BL/6 mice, are highly immunogenic. Rpf-like proteins elicit immunoglobulin G1 (IgG1) and IgG2a responses and T-cell proliferation and stimulate production of gamma interferon, interleukin-10 (IL-10), and IL-12 but not IL-4 or IL-5. Both humoral and T-cell responses against these antigens show a high degree of cross-reactivity. Vaccination of mice with Rpf-like proteins results in a significant level of protection against a subsequent high-dose challenge with virulent M. tuberculosis H37Rv, both in terms of survival times and mycobacterial multiplication in lungs and spleens.

CD44 is a macrophage binding site for Mycobacterium tuberculosis that mediates macrophage recruitment and protective immunity against tuberculosis

Cell migration and phagocytosis are both important for controlling Mycobacterium tuberculosis infection and are critically dependent on the reorganization of the cytoskeleton. Since CD44 is an adhesion molecule involved in inflammatory responses and is connected to the actin cytoskeleton, we investigated the role of CD44 in both these processes. Macrophage (Mphi) recruitment into M. tuberculosis-infected lungs and delayed-type hypersensitivity sites was impaired in CD44-deficient (CD44(-/-)) mice. In addition, the number of T lymphocytes and the concentration of the protective key cytokine IFN-gamma were reduced in the lungs of infected CD44(-/-) mice. The production of IFN-gamma by splenocytes of CD44(-/-) mice was profoundly increased upon antigen-specific stimulation. Flow cytometry analysis revealed that soluble CD44 can directly bind to virulent M. tuberculosis. Mycobacteria also interacted with Mphi-associated CD44, as reflected by reduced binding and internalization of bacilli by CD44(-/-) Mphis. This suggests that CD44 is a receptor on Mphis for binding of M. tuberculosis. CD44(-/-) mice displayed a decreased survival and an enhanced mycobacterial outgrowth in lungs and liver during pulmonary tuberculosis. In summary, we have identified CD44 as a new Mphi binding site for M. tuberculosis that mediates mycobacterial phagocytosis, Mphi recruitment, and protective immunity against pulmonary tuberculosis.

Different innate ability of I/St and A/Sn mice to combat virulent Mycobacterium tuberculosis: phenotypes expressed in lung and extrapulmonary macrophages

Mice of the I/St and A/Sn inbred strains display a severe and moderate course, respectively, of disease caused by Mycobacterium tuberculosis. Earlier, we showed that the response to mycobacterial antigens in I/St mice compared to that in A/Sn mice is shifted toward Th2-like reactivity and a higher proliferative activity and turnover of T cells. However, the physiologic basis for different expressions of tuberculosis severity in these mice remains largely unknown. Here, we extend our previous observations with evidence that I/St interstitial lung macrophages are defective in the ability to inhibit mycobacterial growth and to survive following in vitro infection with M. tuberculosis H37Rv. A unique feature of this phenotype is its exclusive expression in freshly isolated lung macrophages. The defect is not displayed in ex vivo macrophages obtained from the peritoneal cavity nor in macrophages developed in vitro from progenitors extracted from various organs, including the lung itself. In addition, we show that, in sharp contrast to peritoneal macrophages, the mycobactericidal capacity of lung macrophages is not elevated in the presence of exogenous gamma interferon. Our data suggest that the in vivo differentiation in a particular anatomical microenvironment determines the pattern of macrophage-mycobacterium interaction. Thus, caution should be exercised when conclusions based upon the results obtained in a particular in vitro system are generalized to the functions of all phagocytes during M. tuberculosis infection.

Characterization of lung gamma delta T cells following intranasal infection with Mycobacterium bovis bacillus Calmette-Guérin

The lungs are considered to have an impaired capacity to contain infection by pathogenic mycobacteria, even in the presence of effective systemic immunity. In an attempt to understand the underlying cellular mechanisms, we characterized the gammadelta T cell population following intranasal infection with Mycobacterium bovis bacillus Calmette-Guérin (BCG). The peak of gammadelta T cell expansion at 7 days postinfection preceded the 30 day peak of alphabeta T cell expansion and bacterial count. The expanded population of gammadelta T cells in the lungs of BCG-infected mice represents an expansion of the resident Vgamma2 T cell subset as well as an influx of Vgamma1 and of four different Vdelta gene-bearing T cell subsets. The gammadelta T cells in the lungs of BCG-infected mice secreted IFN-gamma following in vitro stimulation with ionomycin and PMA and were cytotoxic against BCG-infected peritoneal macrophages as well as against the uninfected J774 macrophage cell line. The cytotoxicity was selectively blocked by anti-gammadelta TCR mAb and strontium ions, suggesting a granule-exocytosis killing pathway. Depletion of gammadelta T cells by injection of specific mAb had no effect on the subsequent developing CD4 T cell response in the lungs of BCG-infected mice, but significantly reduced cytotoxic activity and IFN-gamma production by lung CD8 T cells. Thus, gammadelta T cells in the lungs might help to control mycobacterial infection in the period between innate and classical adaptive immunity and may also play an important regulatory role in the subsequent onset of alphabeta T lymphocytes.

Expression of L-Selectin (CD62L), CD44, and CD25 on activated bovine T cells

Mycobacterium bovis infection of cattle represents a natural host-pathogen interaction and, in addition to its economic and zoonotic impact, represents a model for human tuberculosis. Extravasation and trafficking of activated lymphocytes to inflammatory sites is modulated by differential expression of multiple surface adhesion molecules. However, effects of M. bovis infection on adhesion molecule expression have not been characterized. To determine these changes, peripheral blood mononuclear cells from M. bovis-infected cattle were stimulated with M. bovis purified protein derivative (PPD) or pokeweed mitogen (PWM) and evaluated concurrently for proliferation and activation marker expression. Stimulation with PPD or PWM increased CD25 and CD44 mean fluorescence intensity (MFI) and decreased CD62L MFI on CD4(+) cells from infected animals. CD62L MFI on PPD- and PWM-stimulated gammadelta T-cell receptor-positive (TCR(+)) and CD8(+) cells was also reduced compared to that of nonstimulated gammadelta TCR(+) and CD8(+) cells. Using a flow cytometry-based proliferation assay, it was determined that proliferating cells, regardless of lymphocyte subset, exhibited increased expression of CD25 and CD44 and decreased expression of CD62L compared to cells that had not proliferated. In contrast to proliferation, activation-induced apoptosis of CD4(+) cells resulted in a significant down regulation of CD44 expression. Lymphocytes obtained from lungs of M. bovis-infected cattle also had reduced expression of CD44 compared to lymphocytes from lungs of noninfected cattle. These alterations in surface molecule expression upon activation likely impact trafficking to sites of inflammation and the functional capacity of these cells within tuberculous granulomas.

Transgenic mice expressing human interleukin-10 in the antigen-presenting cell compartment show increased susceptibility to infection with Mycobacterium avium associated with decreased macrophage effector function and apoptosis

Interleukin-10 (IL-10) is thought to play an important role in the regulation of microbial immunity. While T-cell-derived IL-10 has been shown to suppress cell-mediated immunity, there has been debate as to whether antigen presenting cell (APC)-derived cytokine can perform the same function in vivo. To assess the influence of APC-produced IL-10 on host resistance to mycobacterial infection, transgenic mice expressing human IL-10 under the control of the major histocompatibility complex class II promoter (hu10Tg) were infected with Mycobacterium avium, and bacterial burdens and immune responses were compared with those observed in wild-type (wt) animals. Hu10Tg mice harbored substantially higher numbers of M. avium and succumbed 16 to 18 weeks postinfection. The granulomas in infected hu10Tg mice showed marked increases in both acid-fast bacilli and host macrophages. In addition, these animals displayed a dramatic increase in hepatic fibrosis. The increased susceptibility of the hu10Tg mice to M. avium infection is independent of T-cell-produced endogenous murine IL-10, since bacterial burdens in mice derived by crossing hu10Tg mice with murine IL-10-deficient mice were not significantly different from those in hu10Tg mice. Importantly, gamma interferon (IFN-gamma) responses were not decreased in the infected transgenic animals from those in wt animals, suggesting the normal development of Th1 effector cells. In contrast, mycobacterium-induced macrophage apoptosis as well as production of TNF, nitric oxide, and IL-12p40 were strongly inhibited in hu10Tg mice. Together, these data indicate that APC-derived IL-10 can exert a major inhibitory effect on control of mycobacterial infection by a mechanism involving the suppression of macrophage effector function and apoptosis.

Genetic aspects and microenvironment affect expression of CD18 and VLA-4 in experimental tuberculosis

Control of infection by Mycobacterium tuberculosis is dependent on macrophage activation and efficient migration of effector T-cell populations. Lymphocyte differentiation is associated with changes in cell surface phenotype and alterations in the migratory pattern of these cells. In this study, we investigated the expression of adhesion receptors involved in activation and migration process in experimental tuberculosis. We observed that susceptible BALB/c mice infected with virulent M. tuberculosis by intraperitoneal route presented downmodulation of very late antigen 4 (VLA-4) and unchanged levels of CD18 and CD44hi on peritoneal lymphocytes. On the other hand, lymphocytes from resistant C57BL/6 mice infected by the same route showed unchanged levels of VLA-4 and upregulation of CD18 and CD44hi. However, when BALB/c mice were infected by intratracheal route, lung lymphocytes presented a different pattern of CD18, CD44hi and VLA-4 expression from that observed on peritoneal cells, characterized by unchanged levels of VLA-4 and upregulation of CD18 and CD44hi- coincidentally the same phenotype found on peritoneal cells from C57BL/6. These results suggest that susceptibility and resistance to M. tuberculosis infection, depending on the experimental model, are related to the expression of CD18, CD44hi and VLA-4. Moreover, the microenvironment at the site of infection seems to differentially regulate the expression of these receptors. Thus, the up- or downmodulation of these adhesion receptors is probably associated with differential recruitment of T cells at the site of infection, which may or may not mediate protection in experimental tuberculosis.

Dissemination of Mycobacterium tuberculosis is influenced by host factors and precedes the initiation of T-cell immunity

We report that dissemination of Mycobacterium tuberculosis in the mouse is under host control and precedes the initiation of T-cell immunity. Nine to eleven days after aerosol inoculation, M. tuberculosis disseminates to the pulmonary lymph nodes (LN), where M. tuberculosis-specific T cells are detected 2 to 3 days thereafter. This indicates that the initial spread of bacteria occurs via lymphatic drainage and that the acquired T-cell immune response is generated in the draining LN. Dissemination to peripheral sites, such as the spleen and the liver, occurs 11 to 14 days postinfection and is followed by the appearance of M. tuberculosis-specific T cells in the lung and the spleen. In all cases studied, dissemination to the LN or the spleen preceded activation of M. tuberculosis-specific T cells in that organ. Interestingly, bacteria disseminate earlier from the lungs of resistant C57BL/6 mice than from the lungs of susceptible C3H mice, and consequently, C57BL/6 mice generate an immune response to M. tuberculosis sooner than C3H mice generate an immune response. Thus, instead of spreading infection, early dissemination of M. tuberculosis may aid in the initiation of an appropriate and timely immune response. We hypothesize that this early initiation of immunity following inoculation with M. tuberculosis may contribute to the superior resistance of C57BL/6 mice.

Intranasal BCG vaccination protects BALB/c mice against virulent Mycobacterium bovis and accelerates production of IFN-gamma in their lungs

Local immune reactivity in the lungs of BALB/c mice was studied following (i) intranasal (i.n.) vaccination with Mycobacterium bovis BCG, (ii) intravenous (i.v.) challenge with a virulent M. bovis field isolate and (iii) i.n. vaccination with M. bovis BCG followed by i.v. challenge with an M. bovis field isolate. The results demonstrated that i.n. vaccination with BCG induced a high degree of protection against systemic M. bovis challenge, and that this protection correlated with a rapid production of IFN-gamma after M. bovis challenge by lung T cells from vaccinated mice.

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.

Comparative analysis of T lymphocytes recovered from the lungs of mice genetically susceptible, resistant, and hyperresistant to Mycobacterium tuberculosis-triggered disease

Genetic control of susceptibility to tuberculosis (TB) is being intensively studied, and immune responses to mycobacteria are considerably well characterized. However, it remains largely unknown which parameters of response distinguish resistant and susceptible TB phenotypes. Mice of I/St and A/Sn inbred strains and (A/Sn x I/St)F(1) hybrids were previously categorized as, respectively, susceptible, resistant, and hyperresistant to Mycobacterium tuberculosis-triggered disease. In the present work we compared parameters of lung T cell activation and response following M. tuberculosis challenge. In all mice, the disease progression was accompanied by a marked accumulation in the lungs of activated CD4(+) (CD44(high)/CD45RB(low)) and CD8(+) (CD44(high)/CD45RB(+)) T cells capable of secreting IFN-gamma and of activating macrophages for NO production and mycobacterial growth inhibition. However, significantly more CD8(+) T cells were accumulated in the lungs of resistant A/Sn and F(1) compared with I/St mice. About 80% A/Sn and F(1) CD8(+) cells expressed CD44(high)/CD45RB(+) phenotype, while about 40% I/St CD8(+) cells did not express CD45RB marker at week 5 of infection. In contrast, in susceptible I/St mice lung CD4(+) cells proliferated much more strongly in response to mycobacterial sonicate, and a higher proportion of these cells expressed CD95 and underwent apoptosis compared with A/Sn cells. Unseparated lung cells and T cells of I/St origin produced more IL-5 and IL-10, respectively, whereas their A/Sn and F1 counterparts produced more IFN-gamma following infection. F(1) cells overall expressed an intermediate phenotype between the two parental strains. Such a more balanced type of immune reactivity could be linked to a better TB defense.

Comparative analysis of mycobacterial infections in susceptible I/St and resistant A/Sn inbred mice

SETTING

The availability and appropriate use of animal models is of significant importance for a better and more detailed understanding of the genetic, immunological and pathological mechanisms underlying the development of mycobacterial disease in humans.

OBJECTIVE

To define a mouse model for tuberculosis severity that can be easily adapted to genetic and immunological analysis of host response to Mycobacterium tuberculosis infection.

DESIGN

We describe here two inbred strains of mice, I/St and A/Sn (both Nramp1'), that differ vastly in commonly used parameters of susceptibility to infection with virulent and attenuated strains of M. tuberculosis.

RESULTS

Following infection with a high dose of virulent H37Rv. M. tuberculosis and compared to their resistant A/Sn counterparts, I/St mice displayed more than a 2-fold shorter mean survival time and a more rapid onset and progression of severe body weight loss (cachexia). Moreover, I/St mice supported 20-100-fold higher multiplication of M. tuberculosis following challenge with H37Rv over a large range of infectious inocula. The high susceptibility of I/St mice was also reflected by more severe lung histopathology as evidenced by larger and more numerous lung granuloma and macrophage dominated cellular infiltrates. Finally, we determined that I/St are also unable to control infection with attenuated H37Ra M. tuberculosis and two strains of M. bovis (BCG and Ravenel) indicating hyper-susceptibility of the I/St mouse strain to mycobacterial infections.

CONCLUSIONS

The results of our experiments suggest that comparative analysis of resistant A/Sn and susceptible I/St mice provides an ideal way to study host dependent aspects of tuberculosis susceptibility under the controlled conditions provided by an animal model.

Characterization of T cell clones derived from lymph nodes and lungs of Pseudomonas aeruginosa-susceptible and resistant mice following immunization with heat-killed bacteria

Pseudomonas aeruginosa-resistant BALB/c and susceptible C57Bl/6 (B6) mice were immunized with heat-killed Pseudomonas either in the foot pad or via the trachea, and panels of Pseudomonas-specific T cell clones were developed from lymph nodes and lungs. All clones from either strain, whether of lymph node or lung origin, were CD3+CD4+CD8-TCRalphabeta+. The efficacy of cloning from lymph node cells was comparable between BALB/c and B6 mice. All lymph node BALB/c clones proliferated in response to Pseudomonas antigen in a dose-dependent manner, and this response was MHC class II-restricted. Vigorous proliferation by a considerable proportion of B6 T cell clones occurred in the absence of specific antigen. Lymph node clones from either strain could be categorized as either Th1 or Th0 on the basis of interferon-gamma (IFN-gamma)/IL-4 production. In either mouse strain the efficacy of cloning from lung tissue was substantially lower than from lymph nodes, but the efficacy of cloning from BALB/c compared with B6 lungs was higher. Four lung T cell clones from BALB/c and two from B6 mice were expanded for further analyses, and an interstrain difference was observed in cytokine production. Both B6 lung T cell clones were Th1-like and produced IFN-gamma but not IL-4 and IL-10, whereas four BALB/c lung T cell clones were Th2-like and produced IL-4 and IL-10 but not IFN-gamma. These observations suggest that differences in the CD4+ Th response in the lung may contribute to differences among inbred mouse strains in the level of resistance to bronchopulmonary Pseudomonas infection.

Peculiarities of in vitro immune response to mycobacterial antigens in inbred I/St mice

Comparative study on inbred mouse stains showed that in vitro response of T lymphocytes from tuberculosis-susceptible I/St mice to mycobacterial antigens did not differ from that of T lymphocytes from resistant mouse strains. The defect appeared only in the presence of virulent mycobacteria and was not related to T lymphocytes.

The 19-kD antigen and protective immunity in a murine model of tuberculosis

The 19-kD antigen is a cell wall-associated lipoprotein present in Mycobacterium tuberculosis and in bacille Calmette-Guérin (BCG) vaccine strains. Expression of the 19-kD antigen as a recombinant protein in two saprophytic mycobacteria-M. vaccae and M. smegmatis-resulted in abrogation of their ability to confer protection against M. tuberculosis in a murine challenge model, and in their ability to prime a DTH response to cross-reactive mycobacterial antigens. Induction of an immune response to the 19-kD antigen by an alternative approach of DNA vaccination had no effect on subsequent M. tuberculosis challenge. These results are consistent with a model in which the presence of the 19-kD protein has a detrimental effect on the efficacy of vaccination with live mycobacteria. Targeted inactivation of genes encoding selected antigens represents a potential route towards development of improved vaccine candidates.

Early emergence of CD8(+) T cells primed for production of type 1 cytokines in the lungs of Mycobacterium tuberculosis-infected mice

Several lines of evidence suggest that CD8 T cells are important in protection against tuberculosis. To understand the function of this cell population in the immune response against Mycobacterium tuberculosis, T cells from lungs of M. tuberculosis-infected mice were examined by flow cytometry. The kinetics of the appearance of CD8 T cells in lungs of infected mice closely paralleled that of CD4 T cells. Both CD4(+) and CD8(+) T cells displaying an activated phenotype were found in the lungs as early as 1 week postinfection. By 2 weeks, total cell numbers in the lungs had tripled and percentages of T cells were increased two- to threefold; the percentages of CD4(+) T cells were ca. twofold higher than those of CD8(+) T cells. Short-term stimulation with M. tuberculosis-infected antigen-presenting cells induced cytokine production by primed CD4(+) and CD8(+) T cells. Intracellular cytokine staining revealed that 30% +/- 5% of CD4(+) and 23% +/- 4% of CD8(+) T cells were primed for production of gamma interferon (IFN-gamma). However, a difference in in vivo IFN-gamma production by T cells was observed with approximately 12% of CD4(+) T cells and approximately 5% of CD8(+) T cells secreting cytokine in the lungs at any given time during infection. The data presented indicate that although early in infection the majority of IFN-gamma is produced by CD4(+) T cells, cytokine-producing CD8(+) T cells are readily available when triggered by the appropriate stimuli.