Significant host heterogeneity in susceptibility to tuberculosis exists both between and within mammalian species. Using a mouse model of infection with virulent Mycobacterium tuberculosis (Mtb), we identified the genetic locus sst1 that controls the progression of pulmonary tuberculosis in immunocompetent hosts. In this study, we demonstrate that within the complex, multigenic architecture of tuberculosis susceptibility, sst1 functions to control necrosis within tuberculosis lesions in the lungs; this lung-specific sst1 effect is independent of both the route of infection and genetic background of the host. Moreover, sst1-dependent necrosis was observed at low bacterial loads in the lungs during reactivation of the disease after termination of anti-tuberculosis drug therapy. We demonstrate that in sst1-susceptible hosts, nonlinked host resistance loci control both lung inflammation and production of inflammatory mediators by Mtb-infected macrophages. Although interactions of the sst1-susceptible allele with genetic modifiers determine the type of the pulmonary disease progression, other resistance loci do not abolish lung necrosis, which is, therefore, the core sst1-dependent phenotype. Sst1-susceptible mice from tuberculosis-resistant and -susceptible genetic backgrounds reproduce a clinical spectrum of pulmonary tuberculosis and may be used to more accurately predict the efficacy of anti-tuberculosis interventions in genetically heterogeneous human populations.

Coexistence of pulmonary tuberculosis (TB) and lung cancer in clinic poses significant challenges for the diagnostic and treatment of both diseases. Although association of chronic inflammation and cancer is welldocumented, causal relationship between TB infection and lung cancer are not understood. We present experimental evidence that chronic TB infection induces cell dysplasia and squamous cell carcinoma (SCC) in a lung-specific manner. First, squamous cell aggregates consistently appeared within the lung tissue associated with chronic TB lesions, and in some cases resembled SCCs. A transplantable tumor was established after the transfer of cells isolated from TB lung lesions into syngeneic recipients. Second, the (Mycobacterium tuberculosis) MTB-infected macrophages play a pivotal role in TBinduced carcinogenesis by inducing DNA damage in their vicinity and by the production of a potent epidermal growth factor epiregulin, which may serve as a paracrine survival and growth factor responsible for squamous metaplasia and tumorigenesis. Third, lung carcinogenesis during the course of chronic TB infection was more pronounced in animals with severe lung tissue damage mediated by TB-susceptibility locus sst1. Together, our experimental findings showed a causal link between pulmonary TB and lung tumorigenesis and established a genetic model for further analysis of carcinogenic mechanisms activated by TB infection.

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 × I/St)F1 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+ (CD44high/CD45RBlow) and CD8+ (CD44high/CD45RB+) T cells capable of secreting IFN-γ 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 F1 compared with I/St mice. About 80% A/Sn and F1 CD8+ cells expressed CD44high/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-γ following infection. F1 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.

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Mycobacterium tuberculosis is responsible for almost 2 million deaths annually. Mycobacterium bovis bacillus Calmette-Guérin, the only vaccine available against tuberculosis (TB), induces highly variable protection against TB, and better TB vaccines are urgently needed. A prerequisite for candidate vaccine Ags is that they are immunogenic and expressed by M. tuberculosis during infection of the primary target organ, that is, the lungs of susceptible individuals. In search of new TB vaccine candidate Ags, we have used a genome-wide, unbiased Ag discovery approach to investigate the in vivo expression of 2170 M. tuberculosis genes during M. tuberculosis infection in the lungs of mice. Four genetically related but distinct mouse strains were studied, representing a spectrum of TB susceptibility controlled by the supersusceptibility to TB 1 locus. We used stringent selection approaches to select in vivo–expressed M. tuberculosis (IVE-TB) genes and analyzed their expression patterns in distinct disease phenotypes such as necrosis and granuloma formation. To study the vaccine potential of these proteins, we analyzed their immunogenicity. Several M. tuberculosis proteins were recognized by immune cells from tuberculin skin test-positive, ESAT6/CFP10-responsive individuals, indicating that these Ags are presented during natural M. tuberculosis infection. Furthermore, TB patients also showed responses toward IVE-TB Ags, albeit lower than tuberculin skin test-positive, ESAT6/CFP10-responsive individuals. Finally, IVE-TB Ags induced strong IFN-γ+/TNF-α+ CD8+ and TNF-α+/IL-2+ CD154+/CD4+ T cell responses in PBMC from long-term latently M. tuberculosis–infected individuals. In conclusion, these IVE-TB Ags are expressed during pulmonary infection in vivo, are immunogenic, induce strong T cell responses in long-term latently M. tuberculosis–infected individuals, and may therefore represent attractive Ags for new TB vaccines.

Using a mouse model for genetic analysis of host resistance to virulent Mycobacterium tuberculosis, we have identified a genetic locus sst1 on mouse chromosome 1, which controls progression of pulmonary tuberculosis. In vitro, this locus had an effect on macrophage-mediated control of two intracellular bacterial pathogens, M. tuberculosis and Listeria monocytogenes. In this report, we investigated a specific function of the sst1 locus in antituberculosis immunity in vivo, especially its role in control of pulmonary tuberculosis. We found that the sst1 locus affected neither activation of Th1 cytokine-producing T lymphocytes, nor their migration to the lungs, but rather controlled an inducible NO synthase-independent mechanism of innate immunity. Although the sst1S macrophages responded to stimulation with IFN-γ in vitro, their responsiveness to activation by T cells was impaired. Boosting T cell-mediated immunity by live attenuated vaccine Mycobacterium bovis bacillus Calmette-Guérin or the adoptive transfer of mycobacteria-activated CD4+ T lymphocytes had positive systemic effect, but failed to improve control of tuberculosis infection specifically in the lungs of the sst1S animals. Thus, in the mouse model of tuberculosis, a common genetic mechanism of innate immunity mediated control of tuberculosis progression in the lungs and the efficiency of antituberculosis vaccine. Our data suggest that in immunocompetent humans the development of pulmonary tuberculosis and the failure of the existing vaccine to protect against it, in some cases, may be explained by a similar defect in a conserved inducible NO synthase-independent mechanism of innate immunity, either inherited or acquired.

We previously demonstrated that mice of the I/St strain are extremely susceptible to Mycobacterium tuberculosis, as well as to the taxonomically distant intracellular bacteria Chlamydia pneumoniae and Salmonella enterica. To broaden our knowledge about the control of susceptibility to intracellular pathogens, we studied the infection caused by Mycobacterium avium virulent strain 724 in a panel of inbred mouse strains and found that I/St mice are resistant to M. avium. By comparing I/St mice with B6 mice, we demonstrated that (i) B6 mice are much more susceptible to infection caused by M. avium in terms of bacterial multiplication in the lung tissue and severity of lung pathology; (ii) in B6 mice but not in I/St mice infection leads to prolonged leukocyte infiltration of the lung tissue, development of necrotic lung granulomata, and lethality; and (iii) the unfavorable infectious course in B6 mice is accompanied by elevated production of gamma interferon, tumor necrosis factor alpha, and especially interleukin-12 in the lungs. Importantly, M. avium-resistant I/St mice carry a functional r allele of the Slc11a1 (formerly Nramp1) gene, while B6 mice have the Slc11a1 s genotype. Segregation genetic analysis of (I/St × B6) F2 hybrids demonstrated that susceptibility or resistance to infection caused by M. avium largely depended upon the Slc11a1 genotype and that other genetic traits had a relatively weak influence. This close-to-monogenic pattern differs sharply from the host control of many other intracellular bacterial infections, for which the involvement of numerous quantitative trait loci has been ubiquitously observed.

Immunologic memory induced by pathogenic agents or vaccinations is inextricably linked to long-lasting protection. Adequately maintained memory T and B cell pools assure a fast, effective, and specific response against re-infections. Studies of immune responses amongst residents of malaria endemic areas suggest that memory responses to Plasmodia antigens appear to be neither adequately developed nor maintained, because persons who survive episodes of childhood malaria remain vulnerable to persistent or intermittent malaria infections. By contrast, multiple exposures of humans and laboratory rodents to radiation-attenuated Plasmodia sporozoites (γ-spz) induces sterile and long-lasting protection against experimental sporozoite challenge. Protection is associated with MHC-class I-dependent CD8 T cells, the key effectors against pre-erythrocytic stage infection. We have adopted the P. berghei γ-spz mouse model to study memory CD8 T cells that are specific for antigens expressed by Pb liver-stage (LS) parasites and are found predominantly in the liver. On the basis of phenotypic and functional characteristics, we have demonstrated that liver CD8 T cells form two subsets: CD44hiCD62LloKLRG-1+CD107+CD127−CD122loCD8 T effector/effector memory (TE/EM) cells that are the dominant IFN-γ producers and CD44hiCD62LhiKLRG-1−CD107−CD127+CD122hiCD8 T central memory (TCM) cells. In this review, we discuss our observations concerning the role of CD8 TE/EM and CD8 TCM cells in the maintenance of protracted protective immunity against experimental malaria infection. Finally, we present a hypothesis consistent with a model whereby intrahepatic CD8 TCM cells, that are maintained in part by LS-Ag depot and by IL-15-mediated survival and homeostatic proliferation, form a reservoir of cells ready for conscription to CD8 TE/EM cells needed to prevent re-infections.