Anthony A. Frank

Progression of chronic pulmonary tuberculosis in mice aerogenically infected with virulent Mycobacterium tuberculosis

There are several critical differences in the pulmonary granulomatous response to Mycobacterium tuberculosis between the mouse and other animal models such as the guinea pig or rabbit. One key difference is a conspicuous lack of central caseating necrosis in pulmonary lesions of immunologically intact mice. To determine whether normal mice could develop such pathology in response to highly virulent clinical isolates of M. tuberculosis, C57BL/6 mice were infected aerogenically with varying doses of three different strains, and the development of a granulomatous response was followed for as long as a year. Whereas such conditions failed to induce caseating necrosis in the lungs of these mice, all of the infections induced a granulomatous response which progressed similarly. We present here a descriptive report of the gross pathological progression of tuberculosis in the lungs of the mice. In each case, the disease progressed in five discrete stages, which were delineated on the basis of several criteria including the extent of granulomatous involvement, the cell types present, the degree of lymphocyte organization, and the presence of destructive sequelae such as airway epithelium erosion and airway debris. Quicker progression of disease along these five stages was induced by increasing the size of the inoculum or by the more virulent mycobacterial strains. The infections with the virulent strains were not resolved, and the later stages of the granulomatous response coincided with an increasing bacillary load and a loss of organized lymphocytes in the infected lungs which ultimately resulted in the death of the host. These results indicate that although C57BL/6 mice do not manifest a caseating form of pulmonary tuberculosis, they manifest an equally pathogenic granulomatous response which appears as a chronic interstitial fibrosing response that fails to contain the infection at a time that organized lymphocyte involvement wanes in the lung.

Interleukin-6 induces early gamma interferon production in the infected lung but is not required for generation of specific immunity to Mycobacterium tuberculosis infection.

ABSTRACT Immunity to Mycobacterium tuberculosis is dependent upon the generation of a protective gamma interferon (IFN-γ)-producing T-cell response. Recent studies have suggested that interleukin-6 (IL-6) is required for the induction of a protective T-cell response and that IL-4 may suppress the induction of IFN-γ. To evaluate the role of the cytokines IL-6 and IL-4 in the generation of pulmonary immunity to M. tuberculosis, IL-6 and IL-4 knockout mice were infected with M. tuberculosis via aerosol. The absence of IL-6 led to an early increase in bacterial load with a concurrent delay in the induction of IFN-γ. However, mice were able to contain and control bacterial growth and developed a protective memory response to secondary infection. This demonstrates that while IL-6 is involved in stimulating early IFN-γ production, it is not essential for the development of protective immunity against M. tuberculosis. In contrast, while the absence of IL-4 resulted in increased IFN-γ production, this had no significant effect upon bacterial growth.

Transient Loss of Resistance to Pulmonary Tuberculosis in p47 phox−/− Mice

ABSTRACT Mycobacterium tuberculosis is an important respiratory pathogen the growth of which is controlled primarily by cytokine-activated macrophages. One of the principal mediators of this control is nitric oxide; however, superoxide has recently been shown to be protective in systemic mycobacterial infections. To determine whether superoxide is important in controlling M. tuberculosis during primary pulmonary infection, mice lacking the cytosolic p47phox gene (which is essential for effective superoxide production by the NADPH oxidase) were infected aerogenically. The lack of superoxide during an aerosol infection withM. tuberculosis resulted in a significant increase in bacterial growth over the early period of infection. Once antigen-specific gamma interferon-producing lymphocytes were detected in the draining lymph nodes, however, bacterial growth in the lung stopped. One interesting consequence of the lack of superoxide was an increase in neutrophilic infiltrates within the granuloma. This may be a consequence of increased tissue damage due to more rapid bacterial growth or may reflect a role for superoxide in controlling inflammation.

CD4 is required for the development of a protective granulomatous response to pulmonary tuberculosis

To confirm the primary role of CD4 T cells in pulmonary tuberculosis, mice with a disruption of their CD4 gene (CD4 KO) were exposed to an aerosol of Mycobacterium tuberculosis and survival, cellular responses in the lung and granuloma development followed. CD8 and NK cells from the lungs of infected CD4 KO mice expressed IFN-gamma and were recruited in numbers similar to those seen in the C57BL/6 mice; recruitment correlated with initial control of bacteria. The major defect in mice lacking CD4 was the significant reduction in total cellular recruitment into the lungs. CD4 KO mice did not generate the typical mononuclear granulomatous lesions, instead the cellular influx was macrophage in character and was localized as perivascular cuffing. Early control of M. tuberculosis growth is therefore independent of CD4+ cells but such cells are required to ensure recruitment of mononuclear cells to the lung and thus ensure long-term survival.

Effective Preexposure Tuberculosis Vaccines Fail To Protect When They Are Given in an Immunotherapeutic Mode

ABSTRACT Two vaccine formulations previously shown to induce protective immunity in mice and prevention of long-term necrosis in guinea pigs were tested as potential immunotherapeutic vaccines in mice earlier infected by aerosol with Mycobacterium tuberculosis. Neither vaccine had any effect on the course of the infection in the lungs, but both reduced the bacterial load in the spleen. Similarly, inoculation with Mycobacterium bovis BCG had no effect whatsoever and, if given more than once, appeared to induce an increasingly severe pyogranulomatous response in the lungs of these mice.

Boosting Vaccine for Tuberculosis

ABSTRACT An effective new vaccine for the control of tuberculosis is badly needed. While current research attempts to improve vaccination are concentrating on new prophylactic or immunotherapeutic vaccines, virtually no emphasis has been placed on boosting individuals already inoculated with Mycobacterium bovis BCG. It is shown here that mice vaccinated with BCG gradually lose their capacity to resist an aerosol challenge infection as they age. However, if these mice are inoculated with the 30-kDa mycolyl transferase A protein in midlife, after challenge when aged they express levels of protection in the lungs comparable to those of young mice, associated with minimal pathological damage.

Mycobacterium tuberculosis aerogenic rechallenge infections in B cell-deficient mice

OBJECTIVE Use gene disrupted mice to examine the possible role of secretory antibody on resistance to re-exposure to pulmonary tuberculosis. DESIGN Mice deficient in B cells due to targeted gene disruption were infected by aerosol exposure with Mycobacterium tuberculosis. A further set were identically exposed then given isoniazid to clear the infection and establish a state of memory immunity. RESULTS Control of the aerosol infection and generation of gamma interferon proceeded in a similar manner in both naive and memory immune mice, regardless of B cell deficiency. CONCLUSIONS The absence of antibody responses did not affect the course of infection, thus confirming the classical literature that antibody plays no significant protective role.

The progression of chronic tuberculosis in the mouse does not require the participation of B lymphocytes or interleukin-4

The aging process is associated with alterations in the immune system. Some of the changes reported are an increase in the proportion of B lymphocytes, and a shift to a TH2-like cytokine environment. It has been hypothesized that the development of immunopathology within the lung during tuberculosis is linked to increased interleukin-4 (IL-4) production. In addition, a role for B cells in maintaining granuloma integrity has been recently proposed. This study investigated the role of B cells and IL-4 during the long-term course of chronic tuberculosis in mice and showed that the course of Mycobacterium tuberculosis infection in the lungs was not influenced by the absence of B lymphocytes or the TH2 cytokine IL-4.

Lack of Protection in Mice and Necrotizing Bronchointerstitial Pneumonia with Bronchiolitis in Guinea Pigs Immunized with Vaccines Directed against the hsp60 Molecule of Mycobacterium tuberculosis

ABSTRACT In this study, the hsp60 and hsp70 heat shock protein antigens ofMycobacterium tuberculosis were tested as potential vaccine candidates, using purified recombinant protein antigens or antigens encoded in the form of a DNA plasmid vaccine. Guinea pigs vaccinated with a mixture of the two proteins showed no evidence of resistance to low-dose aerosol challenge infection and quickly developed severe lung damage characterized by necrotizing bronchointerstitial pneumonia and bronchiolitis. As a result, we turned instead to a DNA vaccination approach using a plasmid encoding the hsp60 antigen of M. tuberculosis. Although immunogenic in mice, vaccination with plasmid DNA encoding hsp60 was not protective in that model or in the guinea pig model and again gave rise to similar severe lung damage. This study seriously questions the safety of vaccines against tuberculosis that target highly conserved heat shock proteins.

Immunological Basis for Reactivation of Tuberculosis in Mice

ABSTRACT In this study different inbred strains of mice appeared to control and contain a low dose aerosol infection with Mycobacterium tuberculosis in a similar manner, giving rise to a chronic state of disease. Thereafter, however, certain strains gradually began to show evidence of regrowth of the infection, whereas others consistently did not. Using C57BL/6 mice as an example of a resistant strain and CBA/J mice as an example of a strain susceptible to bacterial growth, we found that these animals revealed distinct differences in the cellular makeup of lung granulomas. The CBA/J mice exhibited a generally poor lymphocyte response within the lungs and vastly increased degenerative pathology at a time associated with regrowth of the infection. As a possible explanation for these events, it was then observed that the CBA/J mouse strain was also less able to upregulate adhesion molecules, including CD11a and CD54, on circulating lymphocytes. These results therefore suggest that a failure to control a chronic infection with M. tuberculosis may reflect an inability to localize antigen-specific lymphocytes within the lung.