Factors associated with severe granulomatous pneumonia in Mycobacterium tuberculosis-infected mice vaccinated therapeutically with hsp65 DNA.

Resistant C57BL/6 mice infected in the lungs with Mycobacterium tuberculosis and then therapeutically vaccinated with Mycobacterium leprae-derived hsp65 DNA develop severe granulomatous pneumonia and tissue damage. Analysis of cells accumulating in the lungs of these animals revealed substantial increases in T cells secreting tumor necrosis factor alpha and CD8 cells staining positive for granzyme B. Stimulation of lung cells ex vivo revealed very high levels of interleukin-10, some of which was produced by B-1 B cells. This was probably an anti-inflammatory response, since lung pathology was dramatically worsened in B-cell gene-disrupted mice.

Pulmonary necrosis resulting from DNA vaccination against tuberculosis.

The use of DNA constructs encoding mycobacterial proteins is a promising new approach to vaccination against tuberculosis. A DNA vaccine encoding the hsp60 molecule of Mycobacterium leprae has previously been shown to protect against intravenous infection of mice with Mycobacterium tuberculosis in both the prophylactic and immunotherapeutic modes. It is shown here, however, that this vaccine was not effective in a more realistic aerosol infection model or in a model of latent tuberculosis in the lungs. Moreover, when given in an immunotherapeutic model the immunized mice developed classical Koch reactions characterized by multifocal discrete regions of cellular necrosis throughout the lung granulomas. Similar and equally severe reactions were seen in mice given a vaccine with DNA coding for the Ag85 antigen of M. tuberculosis. This previously unanticipated safety problem indicates that DNA vaccines should be used with caution in individuals who may have already been exposed to tuberculosis.

The study of Mycobacterium leprae infection in interferon-gamma gene--disrupted mice as a model to explore the immunopathologic spectrum of leprosy.

Mycobacterium leprae infection was evaluated in interferon-gamma knockout (GKO) mice. At 4 months, growth of the bacilli in the footpads of GKO mice plateaued a log(10) higher than that in control mice. Control mice exhibited mild lymphocytic and histiocytic infiltrates, whereas GKO mice developed large, unorganized infiltrates of epithelioid macrophages and scattered CD4 and CD8 T cells. Flow cytometric analysis of popliteal lymph node cells demonstrated similar profiles of T cells; however, GKO cells exhibited an elevated proliferative response to M. leprae antigen. Expression of inducible nitric oxide synthase mRNA was decreased in GKO mice, whereas macrophage inflammatory protein-1alpha and interleukin-4 and -10 mRNA expression were augmented. Control and GKO activated macrophages inhibited bacterial metabolism and produced nitrite. Thus, although deficient in an important Th1 cytokine, GKO mice possess compensatory mechanisms to control M. leprae growth and feature elements resembling mid-borderline leprosy in humans.