Tuberculosis vaccination needs to avoid 'decoy' immune reactions.

Current search for a new effective vaccine against tuberculosis involves selected antigens, vectors and adjuvants. These are being evaluated usually by their booster inoculation following priming with Bacillus Calmette-Guerin. The purpose of this article is to point out, that despite being attenuated of virulence, priming with BCG may still involve immune mechanisms, which are not favourable for protection against active disease. It is postulated, that the responsible 'decoy' constituents selected during the evolution of pathogenic tubercle bacilli may be involved in the evasion from bactericidal host resistance and stimulate immune responses of a cytokine phenotype, which lead to the transition from latent closed granulomas to reactivation with infectious lung cavities. The decoy mechanisms appear as favourable for most infected subjects but leading in a minority of cases to pathology which can effectively transmit the infection. It is proposed that construction and development of new vaccine candidates could benefit from avoiding decoy-type immune mechanisms.

Selection of a Single Domain Antibody, Specific for an HLA-Bound Epitope of the Mycobacterial Ag85B Antigen.

T cells recognizing epitopes on the surface of mycobacteria-infected macrophages can impart protection, but with associated risk for reactivation to lung pathology. We aimed to identify antibodies specific to such epitopes, which carry potentials for development toward novel therapeutic constructs. Since epitopes presented in the context of major histocompatibility complex alleles are rarely recognized by naturally produced antibodies, we used a phage display library for the identification of monoclonal human single domain antibody producing clones. The selected 2C clone displayed T cell receptor-like recognition of an HLA-A*0201 bound 199KLVANNTRL207 peptide from the Ag85B antigen, which is known to be an immunodominant epitope for human T cells. The specificity of the selected domain antibody was demonstrated by solid phase immunoassay and by immunofluorescent surface staining of peptide loaded cells of the T2 cell line. The antibody affinity binding was determined by biolayer interferometry. Our results validated the used technologies as suitable for the generation of antibodies against epitopes on the surface of Mycobacterium tuberculosis infected cells. The potential approaches forward the development of antibody in immunotherapy of tuberculosis have been outlined in the discussion.

The secret trumps, impelling the pathogenicity of tubercle bacilli.

Confrontation between invading microbial pathogens and host defense systems involves intricate cellular and molecular interactions. Here we discuss the virulence factors as trumps, overriding the contest in favor of the tubercle bacillus (Mycobacterium tuberculosis). It evolved a number of molecular constituents, which can interfere with antigen presentation and Toll receptor function, thus impairing immune defenses. It also evolved stress responses, which can drive its cell cycle into a non-replicating, low metabolic mode. Although the low counts of latent bacilli prevent their direct detection, we contend that they retain a capacity to survive for long periods in foamy macrophages and within the necrotic parts of lung granulomas. We attributed significance to drainage of M. tuberculosis by the alveolar fluid: while out-flow is responsible for the clearance, the reverse-flow has an important capacity to re-infect the lungs and to transmit the infection to new recipients. We consider the cycling between replicating and latent organisms to be a continuous process, which is a departure from the concept of long-lived dormant organisms, with a capacity to resuscitate. These aspects impinge also on the actions of isoniazid (INH) chemotherapy and on the topography of human lung lesions. Eventually, fibrosis of the connective tissue of the lungs is known to encapsulate lung lesions, thus limiting the impact of both outward and reverse drainage. In conclusion, the novelty of our views on M. tuberculosis-host interactions rests in the dynamic perception of M. tuberculosis latency and its evolutionary importance for the pathogenesis of tuberculosis.

Prevention of the post-chemotherapy relapse of tuberculous infection by combined immunotherapy.

We report that a recently developed combined immunotherapy (CIT) has the capacity to prevent a spontaneous relapse of replicating Mycobacterium tuberculosis bacilli in the lungs of BALB/c, C57Bl/6 or C3H/HeJ strains of mice, following 4weeks of non-sterilising treatment with isoniazid and rifampicin. The CIT regimen, represented by recombinant IFNgamma, anti-alpha crystalline monoclonal IgA antibody and IL-4 neutralizing polyclonal antibody, reduced the 8-week relapse of viable bacterial counts in the lungs most significantly, when CIT was inoculated during the 5th week post infection, i.e. during the 3rd week of chemotherapy. Although CIT enhanced lung granuloma area, nitric oxide, cytokine and chemokine levels in lung washings significantly, these could not be directly associated with the beneficial effect of CIT on the degree of relapse in the lungs. These results represent a proof-of-principle, that the described CIT, when combined with chemotherapy, could have potential for future development of a shorter regimen of tuberculosis treatment.

IL-4 depletion enhances host resistance and passive IgA protection against tuberculosis infection in BALB/c mice.

The influence of Th2 cytokines in tuberculosis has been a matter of dispute. Here we report that IL-4 has a profound regulatory effect on the infection of BALB/c mice with Mycobacterium tuberculosis. Depletion of IL-4 with a neutralizing mAb caused only evanescent reduction of lung infection, but when combined with i.n. inoculations of IgA anti-mycobacterial alpha-crystallin mAb and mouse rIFN-gamma, we observed a 40-fold reduction of the bacterial counts in the lungs at 3 wks following i.n. infection (p<0.001). In genetically deficient IL-4-/- BALB/c mice, infection in both lung and spleen was substantially reduced for up to 8 wks without further treatment. Reconstitution of IL-4-/- mice with rIL-4 increased bacterial counts to wild-type levels and made the mice refractory to protection by IgA/IFN-gamma. Analysis of the lungs showed increased granulomatous infiltration and proinflammatory mediators in anti-IL-4/IgA/IFN-gamma-treated and infected mice. We conclude that the action of IL-4 in tuberculosis is targeted at macrophages and that it may include an antagonistic effect on their IgA/IFN-gamma-induced activation and nitric oxide production. The described novel immunotherapy, combining treatments with anti-IL-4, IgA antibody and IFN-gamma, has potential for translation toward the passive immunoprophylaxis of tuberculosis.

Polymeric IgR knockout mice are more susceptible to mycobacterial infections in the respiratory tract than wild-type mice.

It is generally accepted that cellular, and not humoral immunity, plays the crucial role in defense against intracellular bacteria. However, accumulating data indicate the importance of humoral immunity for the defense against a number of intracellular bacteria, including mycobacteria. We have investigated the role of secretory IgA, the main isotype found in mucosal tissues, in protection against mycobacterial infection, using polymeric IgR (pIgR)-deficient mice. Characterization of the humoral response induced after intra-nasal immunizations with the mycobacterial antigen PstS-1 revealed a loss of antigen-specific IgA response in saliva from the knockout mice. IgA level in the bronchoalveolar lavage of knockout mice was similar to wild-type level, although the IgA antibodies must have reached the lumen by other means than pIgR-mediated transport. Infection with Mycobacterium bovis bacillus Calmette-Guérin (BCG) demonstrated that the immunized pIgR-/- mice were more susceptible to BCG infection than immunized wild-type mice, based on higher bacterial loads in the lungs. This was accompanied by a reduced production of both IFN-gamma and tumor necrosis factor-alpha (TNF-alpha) in the lungs. Additionally, the pIgR-/- mice displayed reduced natural resistance to mycobacterial infection proved by significantly higher bacterial growth in their lungs compared with wild-type mice after infection with virulent Mycobacterium tuberculosis. The knockout mice appeared to have a delayed mycobacteria-induced immune response with reduced expression of protective mediators, such as IFN-gamma, TNF-alpha, inducible nitric oxide synthase and regulated upon activation normal T cell sequence, during early infection. Collectively, our results show that actively secreted IgA plays a role in protection against mycobacterial infections in the respiratory tract, by blocking entrance of bacilli into the lungs, in addition to modulation of the mycobacteria-induced pro-inflammatory response.

Characterization of HLA-DR- and TCR-binding residues of an immunodominant and genetically permissive peptide of the 16-kDa protein of Mycobacterium tuberculosis.

The 16-kDa protein of Mycobacterium tuberculosis represents an important antigenic target during bacillary latency and, consequently, should be considered as candidate subunit vaccine component. In this study, we have used CD4 T cell clones that recognize the peptide p91-110, an immunodominant and genetically permissive epitope, in the context of five different HLA-DR molecules and truncated and substituted variants of this peptide, to identify the minimal binding sequence (HLA-DR-binding core) and the minimal stimulatory sequence (TCR-binding core), as well as the residues that contact HLA-DR molecules and the TCR. We have found a common 9-mer sequence, spanning amino acids 93-101, as the binding core for HLA-DR1, -DR11, -DR13 and -DR7, but a longer (13-mer) sequence spanning amino acids 92-104 was required for binding to the HLA-DR15 molecules. F(93) was required for binding to all the tested HLA-DR molecules, hence allowing us to identify it as the N-terminal primary anchor residue (P1). Additionally, the binding requirements for other residues varied considerably between the tested alleles: A(94) for HLA-DR15, V(99) for HLA-DR1, -DR15, -DR11 and -DR7, R(100) for HLA-DR11 and -DR13, and L(104) for HLA-DR15. Concerning the residues of p91-110 peptide required for binding to the TCR, the pepscan analysis results would support the contention that P(-1) E(92), P6 F(98) would be important TCR contact sites because their substitutions led to full loss of T cell activation. Moreover, P8 R(100) is found to be critical residue in binding to HLA-DR11- and -DR13-restricted T cell clones, without influencing binding to the relevant HLA-DR molecule. Our results could be useful to design peptides with altered HLA anchor residues or TCR interaction sites to achieve remarkable increase in activity and to study their vaccine potential.

Mouse monoclonal IgA binds to the galectin-3/Mac-2 lectin from mouse macrophage cell lines.

The beta-galactoside-binding S-type lectin galectin-3/Mac-2, expressed among several other cell types on activated macrophages, is known to bind IgE, but not other Ig classes. We report in this paper that the single major constituent in a detergent lysate from the J774 mouse macrophage cell line bound to a mouse monoclonal IgA-affinity column. This fraction has been identified by mass spectrometry analysis as galectin-3. Binding of both mouse IgA and IgE to galectin-3 coated plates was inhibited by lactose and asialofetuin. Furthermore, three different monoclonal IgAs bound also to purified recombinant hamster galectin-3 coated plates in a concentration dependent manner. The potential functional significance of IgA binding to galectin-3 within macrophages and possibly other cell types is discussed.

Mouse IgA inhibits cell growth by stimulating tumor necrosis factor-alpha production and apoptosis of macrophage cell lines.

Potent Fcalpha-mediated actions of IgA have previously been shown for myeloid cells from man, but much less is known in relation to murine cells. Here, we report that mouse monoclonal IgA, irrespective of their antigenic specificity, inhibit the proliferation of mouse macrophage cell lines. The anti-proliferative activity was manifested by both monomeric and polymeric mouse IgA, but not by mouse monoclonal IgG and IgM. Growth of J774 cells was significantly inhibited during the 4-8 days of logarithmic growth, followed by a subsequent recovery of cell numbers prior to the stationary phase. We demonstrated that IgA binds to J774 cells, stimulates tumor necrosis factor (TNF)-alpha production and induces apoptosis which is not dependent on NO or FAS/CD95. We also demonstrated that IgA, in synergy with IFN-gamma, induced TNF-alpha production and apoptosis of thioglycollate-elicited mouse peritoneal macrophages. Thus, the in vitro actions of IgA described may also play a regulatory role for mouse macrophages in vivo.

Passive protection with immunoglobulin A antibodies against tuberculous early infection of the lungs.

We report on a new approach toward protection against tuberculosis, based on passive inoculation with immunoglobulin A (IgA) antibodies. In a mouse model of tuberculous lung infection, intranasal inoculations of mice with an IgA monoclonal antibody (mAb) against the alpha-crystallin antigen of Mycobacterium tuberculosis reduced up to 10-fold the lung bacterial counts at nine days after either aerosol- or intranasal challenge. This effect involved synergism between mAb inoculations shortly before and 3 days after infection. Monomeric IgA reduced the colony-forming unit counts to the same extent as the polymeric IgA, suggesting antibody targeting to Fcalpha, rather than poly-immunoglobulin receptors on infected lung macrophages. The protective effect was of short duration, presumably due to the rapid degradation of the intranasally applied IgA. Our results provide evidence of an alternative approach which could be further developed toward immunoprophylaxis against tuberculosis in immunocompromised subjects.

An anti-inflammatory role for V alpha 14 NK T cells in Mycobacterium bovis bacillus Calmette-Guérin-infected mice.

The possible contribution of NKT cells to resistance to Mycobacterium tuberculosis infection remains unclear. In this paper we characterized the Valpha14 NKT cell population following infection with Mycobacterium bovis bacillus Calmette-Guérin (BCG). BCG infection determined an early expansion of Valpha14 NKT cells in liver, lungs, and spleen, which peaked on day 8 and was sustained until day 30. However, an NK1.1(+) Valpha14 NKT population preferentially producing IFN-gamma predominated at an early stage (day 8), which was substituted by an NK1.1(-) population preferentially producing IL-4 at later stages (day 30). Despite the fact that Valpha14 NKT cell-deficient mice eliminated BCG as did control mice, they had significantly higher numbers of granulomas in liver and lungs. Additionally, while control mice developed organized small granulomas, those in Valpha14 NKT-deficient mice had signs of caseation, large cellular infiltrates, and some multinucleated macrophages, suggesting that Valpha14 NKT cells may actually work as anti-inflammatory cells by limiting excessive lymphocyte influx and tissue pathology. In agreement, we found an increased spontaneous production and mRNA expression of TNF-alpha in liver and lungs of Valpha14 NKT-deficient mice, whose neutralization in vivo by anti-TNF-alpha mAbs consistently reduced the number of granulomas in liver and lungs. Together, our results support a regulatory role for Valpha14 NKT cells in the course of BCG infection through their ability to limit the extent of inflammatory response and point to an important role for this cell subset as a regulator of the balance between protective responses and immunopathology.

T-cell recognition of peptides from the Mycobacterium leprae 35 kDa protein in Thai leprosy patients, healthy contacts, and non-contacts.

The objective of the study was to identify Mycobacterium leprae-specific immunogenic peptides for the development of a skin test reagent. Such a reagent is required for the detection of M. leprae infection and possibly for the diagnosis of patients with active leprosy. For this purpose, we analyzed the in vitro responses of human peripheral blood mononuclear cell (PBMCs) to peptides from the 35 kDa protein of M. leprae. This protein is of interest since it has no homologue within the Mycobacterium tuberculosis complex, although it has a homologue in Mycobacterium avium. The subjects enrolled in the study were paucibacillary (PB) and multibacillary (MB) leprosy patients, healthy contacts, and non-contacts. Seventy-three PB and 124 MB leprosy patients were recruited from four leprosy clinics in Thailand. Fifty-seven healthy contacts were household contacts. Twenty non-leprosy contacts had no family history of or exposure to leprosy. PBMCs from individuals were tested for stimulation with 12 overlapping peptides from the M. leprae 35 kDa protein using the lymphocyte proliferation assay. These peptides were located in four areas containing three to six residues which were distinct for the M. leprae product in comparison to that from M. avium. Four peptides (p60-76, p132-151, p206-224 and p267-286), which were the most permissive from each region and recognized by non-contacts with significantly lower frequencies than other subject groups, were identified. From this preliminary result, we conclude that these four peptides were likely to be M. leprae-specific.

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.

Identification of epitopes of Mycobacterium tuberculosis 16-kDa protein recognized by human leukocyte antigen-A*0201 CD8(+) T lymphocytes.

CD8(+) T cells could make an important contribution to protection against tuberculosis (TB), but the antigenic determinants recognized in the context of major histocompatibility complex class I molecules remain ill defined. Our aim was to identify nonamer peptides derived from the acr/16-kDa antigen. Two immunogenic peptides (p21-29 and p120-128) were identified by their ability to elicit cytotoxic CD8(+) T cells from juvenile patients recovering from TB. Epitope-specific recognition was demonstrated by the lysis of both Mycobacterium tuberculosis-infected and peptide-pulsed macrophages, the release of cytotoxic granules, and interferon-gamma and tumor necrosis factor-alpha production. CD8(+) T cell responses to p21-29 and p120-128 were detected ex vivo in freshly isolated peripheral blood mononuclear cells from patients with TB but not in those from healthy control subjects. Our data suggest that these antigenic peptides can play a critical role in effective immunity against mycobacterial infection and TB.