Antimycobacterial functions in bone-marrow-derived macrophages

Cytokine gene expression by cultures of human lymphocytes with autologous Mycobacterium tuberculosis-infected monocytes

In order to better understand the immunoregulation following Mycobacterium tuberculosis infection, cytokine mRNA induction in response to in vitro infection of human monocytes with live virulent M. tuberculosis H37Rv cocultured with autologous lymphocytes was quantitated by reverse transcriptase-PCR. Induced levels of interleukin 1 beta (IL-1 beta), IL-2, tumor necrosis factor alpha, and gamma interferon (IFN-gamma) were compared among groups of individuals representing three phases of immunity to infection with M. tuberculosis: naive normal control subjects, purified protein derivative (PPD)-reactive normal donors, and individuals with active tuberculosis (TB [diseased]). Levels of IL-1 beta and tumor necrosis factor alpha mRNA in cocultured cells from TB patients were 51 and 45%, respectively, of those obtained in cells from sensitized healthy volunteers and were comparable to those from naive normal donors. Lymphoproliferative responses to M. tuberculosis and induction of the T-cell cytokine IL-2 were predictably high in the cells of PPD-sensitized donors, low in normal naive individuals, and variable among TB patients. In contrast, the induced level of another lymphokine, IFN-gamma, did not follow the pattern seen in IL-2 induction. Infection with live M. tuberculosis induced high levels of IFN-gamma mRNA in lymphocytes of both PPD-sensitized and normal naive donors compared with those of TB patients. Interestingly, polyclonal stimulation with the mitogen concanavalin A induced similar IFN-gamma levels in cells from all three donor groups. The high level of IFN-gamma induced by the infection of monocytes from naive normal donors suggests a role for natural killer (NK) cells in the production of IFN-gamma in this coculture system. This response appears independent of the role performed by T cells.

Immunotherapy of airborne tuberculosis in mice via the lung-specific delivery of cytokines

The immunotherapeutic potential of interleukin-2 (IL-2), tumour necrosis factor alpha (TNFα) and interferon gamma (IFN-γ) administered by aerosol was examined on mice infected with Mycobacterium tuberculosis by the aerogenic route. Infection of balb/c mice with 10(4) colony forming units (cfu) of M tuberculosis led to death of all mice at day 35 post infection after progressive microbial growth in the lungs. Aerosolization of IL-2 (100 μg per mouse) did not promote an increase in resistance to tuberculosis, as seen by growth of M tuberculosis in the lungs. Administration of IFN-γ or TNFα (100 μg) by the aerosol route led to a significant reduction in microbial growth in the lungs and a 100% survival of infected mice at day 60. Similarly, aerosolization of TNFα and IFN-γ combined led to a very high degree of tuberculostatic activity in the lungs of infected animals, but not superior to that seen with either cytokine alone. Administration of similar amounts of cytokines by repeated intraperitoneal infusions led to a very marginal improvement in mouse resistance. These results suggest that localized cytokine administration may be beneficial in the treatment of lung diseases.

A comparison of the different methods available for determining BCG-macrophage interactions in vitro, including a new method of colony counting in broth

Different methods of determining BCG viability based on colony forming unit (CFU) counting and radio-isotope labelling were comparatively assessed. These included radio-isotope labelling with [3H]uracil, [3H]uridine, [3H]glycerol, and CFU counting, by both agar plate dilution, and microcolony counting in broth. The sensitivity ranges of the different techniques were determined in both macrophage-free and macrophage-treated systems and used to assess the anti-mycobacterial potential of human monocyte-derived macrophages following BCG infection.

Modulation of Mycobacterium avium growth in vivo by cytokines: involvement of tumour necrosis factor in resistance to atypical mycobacteria

The protective mechanisms associated with resistance to atypical mycobacteria infections are not clear. In an effort to broaden our understanding of the mechanisms involved, susceptible mice were infected with a virulent strain of M. avium and various treatments were applied so as to modify the course of the disease. Treatment with an antiserum against tumour necrosis factor-alpha (TNF-alpha) significantly enhanced the experimental infection, as judged by enumeration of colony-forming units (CFU) in the spleens and livers of infected mice, suggesting a role for TNF-alpha in resistance to M. avium. In other sets of experiments, recombinant cytokines were directly infused into infected mice. Infusion of recombinant interferon-gamma (IFN-gamma) did not modify the experimental infection significantly, and infusion of interleukin-2 was also without effect. Injection of TNF-alpha enhanced resistance in susceptible animals, as seen by a reduction in the viable bacilli recovered from the spleens and livers. In a final set of experiments, we demonstrate that combinations of cytokines may induce strong resistance against M. avium, namely injection of 1 micrograms of interleukin-1 alpha and 1 micrograms of TNF-alpha at 5-day intervals which was seen to eradicate M. avium in both spleens and livers of susceptible BALB/c mice. Overall, our results suggest that induction of protection against M. avium by treatment with cytokines may be feasible, and that TNF-alpha may be a pivotal molecule in resistance to M. avium.

Interferon-gamma-treated murine macrophages inhibit growth of tubercle bacilli via the generation of reactive nitrogen intermediates

Murine peritoneal macrophages were isolated and their ability to restrict growth of a virulent Mycobacterium tuberculosis in response to IFN-gamma was assessed in various conditions. Doses of IFN-gamma ranging from 10 to 100 U stimulated high levels of antimycobacterial activity, as seen by inhibition of growth. Addition of catalase, superoxide dismutase, and other scavengers of reactive oxygen species before infection failed to abrogate this restriction of growth, suggestive of a lack of involvement of reactive oxygen species in this phenomenon. Addition of arginase before infection inhibited the bacteriostatic ability of IFN-gamma-pulsed macrophages as did addition of NG-monomethyl L-arginine, an inhibitor of the synthesis of inorganic nitrogen oxide. In both cases, this inhibition was reversed by adding excess L-arginine in the medium. Moreover, nitrite production in macrophages was correlated with their ability to restrict tubercle bacilli growth. These results imply that nitric oxide or another inorganic nitrogen oxide is an important effector molecule in restricting growth of M. tuberculosis in IFN-gamma-pulsed murine macrophages.