JoAnne L. Flynn

Tumor necrosis factor-α is required in the protective immune response against mycobacterium tuberculosis in mice

Understanding the immunological mechanisms of protection and pathogenesis in tuberculosis remains problematic. We have examined the extent to which tumor necrosis factor-alpha (TNF alpha) contributes to this disease using murine models in which the action of TNF alpha is inhibited. TNF alpha was neutralized in vivo by monoclonal antibody; in addition, a mouse strain with a disruption in the gene for the 55 kDa TNF receptor was used. The data from both models established that TNF alpha and the 55 kDa TNF receptor are essential for protection against tuberculosis in mice, and for reactive nitrogen production by macrophages early in infection. Granulomas were formed in equal numbers in control and experimental mice, but necrosis was observed only in mice deficient in TNF alpha or TNF receptor. TNF alpha and the 55 kDa TNF receptor are necessary conditions for protection against murine M. tuberculosis infection, but are not solely responsible for the tissue damage observed.

The spectrum of latent tuberculosis: rethinking the biology and intervention strategies

Immunological tests provide evidence of latent tuberculosis in one third of the global population, which corresponds to more than two billion individuals. Latent tuberculosis is defined by the absence of clinical symptoms but carries a risk of subsequent progression to clinical disease, particularly in the context of co-infection with HIV. In this Review we discuss the biology of latent tuberculosis as part of a broad range of responses that occur following infection with Mycobacterium tuberculosis, which result in the formation of physiologically distinct granulomatous lesions that provide microenvironments with differential ability to support or suppress the persistence of viable bacteria. We then show how this model can be used to develop a rational programme to discover effective drugs for the eradication of M. tuberculosis infection.

IL-17 Production Is Dominated by γδ T Cells rather than CD4 T Cells during Mycobacterium tuberculosis Infection

IL-17 is a cytokine produced by T cells in response to IL-23. Recent data support a new subset of CD4 Th cells distinct from Th1 or Th2 cells that produce IL-17 and may contribute to inflammation. In this study, we demonstrate that, in naive mice, as well as during Mycobacterium tuberculosis infection, IL-17 production is primarily from γδ T cells and other non-CD4+CD8+ cells, rather than CD4 T cells. The production of IL-17 by these cells is stimulated by IL-23 alone, and strongly induced by the cytokines, including IL-23, produced by M. tuberculosis-infected dendritic cells. IL-23 is present in the lungs early in infection and the IL-17-producing cells, such as γδ T cells, may represent a central innate protective response to pulmonary infection.

Effects of Tumor Necrosis Factor Alpha on Host Immune Response in Chronic Persistent Tuberculosis: Possible Role for Limiting Pathology

ABSTRACT Reactivation of latent tuberculosis contributes significantly to the incidence of disease caused by Mycobacterium tuberculosis. The mechanisms involved in the containment of latent tuberculosis are poorly understood. Using the low-dose model of persistent murine tuberculosis in conjunction with MP6-XT22, a monoclonal antibody that functionally neutralizes tumor necrosis factor alpha (TNF-α), we examined the effects of TNF-α on the immunological response of the host in both persistent and reactivated tuberculous infections. The results confirm an essential role for TNF-α in the containment of persistent tuberculosis. TNF-α neutralization resulted in fatal reactivation of persistent tuberculosis characterized by a moderately increased tissue bacillary burden and severe pulmonic histopathological deterioration that was associated with changes indicative of squamous metaplasia and fluid accumulation in the alveolar space. Analysis of pulmonic gene and protein expression of mice in the low-dose model revealed that nitric oxide synthase was attenuated during MP6-XT22-induced reactivation, but was not totally suppressed. Interleukin-12p40 and gamma interferon gene expression in TNF-α-neutralized mice was similar to that in control mice. In contrast, interleukin-10 expression was augmented in the TNF-α-neutralized mice. In summary, results of this study suggest that TNF-α plays an essential role in preventing reactivation of persistent tuberculosis, modulates the pulmonic expression of specific immunologic factors, and limits the pathological response of the host.

Tuberculous Granulomas Are Hypoxic in Guinea Pigs, Rabbits, and Nonhuman Primates

ABSTRACT Understanding the physical characteristics of the local microenvironment in which Mycobacterium tuberculosis resides is an important goal that may allow the targeting of metabolic processes to shorten drug regimens. Pimonidazole hydrochloride (Hypoxyprobe) is an imaging agent that is bioreductively activated only under hypoxic conditions in mammalian tissue. We employed this probe to evaluate the oxygen tension in tuberculous granulomas in four animal models of disease: mouse, guinea pig, rabbit, and nonhuman primate. Following infusion of pimonidazole into animals with established infections, lung tissues from the guinea pig, rabbit, and nonhuman primate showed discrete areas of pimonidazole adduct formation surrounding necrotic and caseous regions of pulmonary granulomas by immunohistochemical staining. This labeling could be substantially reduced by housing the animal under an atmosphere of 95% O2. Direct measurement of tissue oxygen partial pressure by surgical insertion of a fiber optic oxygen probe into granulomas in the lungs of living infected rabbits demonstrated that even small (3-mm) pulmonary lesions were severely hypoxic (1.6 ± 0.7 mm Hg). Finally, metronidazole, which has potent bactericidal activity in vitro only under low-oxygen culture conditions, was highly effective at reducing total-lung bacterial burdens in infected rabbits. Thus, three independent lines of evidence support the hypothesis that hypoxic microenvironments are an important feature of some lesions in these animal models of tuberculosis.

Tuberculosis: What We Don’t Know Can, and Does, Hurt Us

Mycobacterium tuberculosis has a penetrance of its host population that would be the envy of most human pathogens. About one-third of the human population would have a positive skin test for the infection and is thus thought to harbor the bacterium. Globally, 22 “high-burden” countries account for more than 80% of the active tuberculosis cases in the world, which shows the inequitable distribution of the disease. There is no effective vaccine against infection, and current drug therapies are fraught with problems, predominantly because of the protracted nature of the treatment and the increasing occurrence of drug resistance. Here we focus on the biology of the host-pathogen interaction and discuss new and evolving strategies for intervention.

Tuberculosis: Latency and Reactivation

Tuberculosis is a major cause of death around the world, with most of the 1.5 million deaths per year attributable to the disease occurring in developing countries. This disease is caused by Mycobacterium tuberculosis , an acid-fast bacillus that is transmitted primarily via the respiratory route.

Experimental Mycobacterium tuberculosis Infection of Cynomolgus Macaques Closely Resembles the Various Manifestations of Human M. tuberculosis Infection

ABSTRACT Nonhuman primates were used to develop an animal model that closely mimics human Mycobacterium tuberculosis infection. Cynomolgus macaques were infected with low doses of virulent M. tuberculosis via bronchoscopic instillation into the lung. All monkeys were successfully infected, based on tuberculin skin test conversion and peripheral immune responses to M. tuberculosis antigens. Progression of infection in the 17 monkeys studied was variable. Active-chronic infection, observed in 50 to 60% of monkeys, was characterized by clear signs of infection or disease on serial thoracic radiographs and in other tests and was typified by eventual progression to advanced disease. Approximately 40% of monkeys did not progress to disease in the 15 to 20 months of study, although they were clearly infected initially. These monkeys had clinical characteristics of latent tuberculosis in humans. Low-dose infection of cynomolgus macaques appears to represent the full spectrum of human M. tuberculosis infection and will be an excellent model for the study of pathogenesis and immunology of this infection. In addition, this model will provide an opportunity to study the latent M. tuberculosis infection observed in ∼90% of all infected humans.

Understanding Latent Tuberculosis: A Moving Target

Tuberculosis (TB) remains a threat to the health of people worldwide. Infection with Mycobacterium tuberculosis can result in active TB or, more commonly, latent infection. Latently infected persons, of which there are estimated to be ~2 billion in the world, represent an enormous reservoir of potential reactivation TB, which can spread to other people. The immunology of TB is complex and multifaceted. Identifying the immune mechanisms that lead to control of initial infection and prevent reactivation of latent infection is crucial to combating this disease.

Chemokine receptor 2 serves an early and essential role in resistance to Mycobacterium tuberculosis

Although the protective cellular immune response to Mycobacterium tuberculosis requires recruitment of macrophages and T lymphocytes to the site of infection, the signals that regulate this trafficking have not been defined. We investigated the role of C-C chemokine receptor 2 (CCR2)-dependent cell recruitment in the protective response to M. tuberculosis. CCR2−/− mice died early after infection and had 100-fold more bacteria in their lungs than did CCR2+/+ mice. CCR2−/− mice exhibited an early defect in macrophage recruitment to the lung and a later defect in recruitment of dendritic cells and T cells to the lung. CCR2−/− mice also had fewer macrophages and dendritic cells recruited to the mediastinal lymph node (MLN) after infection. T cell migration through the MLN was similar in CCR2−/− and CCR2+/+ mice. However, T cell priming was delayed in the MLNs of the CCR2−/− mice, and fewer CD4+ and CD8+ T cells primed to produce IFN-γ accumulated in the lungs of the CCR2−/− mice. These data demonstrate that cellular responses mediated by activation of CCR2 are essential in the initial immune response and control of infection with M. tuberculosis.