Perforin, a cytotoxic molecule which mediates cell necrosis, is not required for the early control of mycobacterial infection in mice

Abstract

Host defense against mycobacterial infection requires the participation of monocytes and T cells. Both CD4+ and CD8+ T cells have been shown to be important in resistance to mycobacterial infection in vivo. The main contribution of CD4+ T cells to the protective antituberculosis response involves the production of Th1-type cytokines, including interleukin-2 (IL-2) and gamma interferon (IFN-gamma). CD8+ T cells have been considered to be responsible primarily for cytotoxicity mediated by toxic molecules, including perforin. CD8+ T cells may also elaborate Th1-type cytokines, such as IFN-gamma, in response to the infection. To elucidate the contribution of perforin-mediated target cell death to the control of mycobacterial infection in vivo, mice with a disruption in the perforin gene (P-/-) were infected with Mycobacterium bovis BCG or M. tuberculosis Erdman for 5 and 13 weeks, respectively. At 1, 3, 5, and 13 weeks postinfection, the number of viable mycobacteria in the lungs, spleens, and livers of mice were determined by CFU assay. The infected tissues were examined histologically, and cytokine mRNA levels in the spleens of these mice were determined. Similar studies were carried out in Fas receptor-defective (CBA/lpr(cg)) mice to evaluate the contribution of this alternative cytotoxic pathway to the control of mycobacterial infection. The absence of either perforin gene function or Fas receptor gene function did not modify the course of experimental mycobacterial infection in these mice. In addition, both P-/- and Fas receptor-defective mice appeared to have a compensatory activation of cytokine genes, even in the absence of the experimental infection. P-/- mice had a mean 3.4- to 5-fold increase in mRNA levels for IL-10, IL-12p35, IL-6, and IFN-gamma. Similarly, Fas receptor-defective mice had a mean 3- to 3.6-fold increase in mRNA levels for IFN-gamma, IL-12p35, and IL-10. Our results indicate that both perforin-mediated cytotoxicity and Fas-mediated cytotoxicity do not appear to be necessary for the early control of mycobacterial infection in vivo.

The relative contribution of antibody production and CD8+ T cell function to immune control of Trypanosoma cruzi

“…Perforin/granzyme mediated cytolysis involves the release of granules containing perforin, which polymerizes to form pores in the target cell membrane, and granzymes which may enter through these pores and induce apoptosis of the target cell (Berke, 1995, Kagi et al 1996b). The generation of knockout mice lacking perforin or granzyme B has allowed investigators to explore the role of this pathway in CD8 þ T cell response in a number of systems (Heusel et al 1994, Kagi et al 1994a, b, Guidotti and Chisari, 1996, Denkers et al 1997, Laochumroonvorapong et al 1997, Renggli et al 1997, Tang et al 1997. In the present work we show that in T. cruzi infection, perforin/ granzyme-mediated cytolysis plays a rather minor role in the protective capacity of CD8 þ T cells.…”

Views of immunology: effector T cells

“…In addition, perforin-deficient mice controlled aerosol M. tuberculosis challenge equivalently to wildtype mice in the late phase of infection as well (14). Finally, perforin-deficient mice and wildtype mice infected with bacille Calmette-Guérin (BCG) or M. tuberculosis intravenously demonstrated equivalent bacterial burdens (15). By contrast, as discussed below, mice deficient in IFN-c or TNF-a demonstrate striking susceptibility to M. tuberculosis infection.…”

Cytotoxic T cells and mycobacteria

“…Immunity during the ¢rst few weeks of infection was unimpaired in mice in which the genes for either perforin or granzyme B (a cytotoxic granule protease that contributes to apoptosis) had been knocked out [53]. Protection against BCG also appeared normal in Fasdefective mice [54]. However, since there are multiple pathways of cytotoxicity and multiple lytic and cytotoxic proteins in cytotoxic granules, some redundancy might be expected.…”

“…It may account for the major component of the protective e¡ect of these clones that was resistant to neutralization in vivo by injection of antibody against IFN-Q [46]. Although others found that knockout mice that do not express the perforin gene did not have decreased resistance to the early stages of tuberculosis [53,54], this defence mechanism may be more important later in infection. Our high-dose intravenous challenge model probably resembles late-stage rather than early-stage tuberculosis.…”