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Gamma interferon-mediated cytotoxicity related to murine Chlamydia trachomatis infection
G I Byrne1, B Grubbs, T J Marshall
1Department of Medical Microbiology, University of Wisconsin Medical School, Madison 53706.
Abstract:
After infection with the mouse pneumonitis agent (MoPn; murine Chlamydia trachomatis), heterozygous (nu/+) but not nude athymic (nu/nu) mice produced enhanced amounts of gamma interferon (IFN-gamma) in vitro in response to MoPn antigen that exhibited cytotoxic activity when added to host cells already infected with chlamydiae. Antibody-complement lysis showed the cytotoxic activity to be dependent, at least in part, on L3T4+ T cells for production. The cytotoxic responses were directed primarily against Chlamydia-infected target cells, but a second type of toxicity was demonstrable against uninfected target cells after treatment of the generating cell population with anti-Lyt-2 antibody plus complement at certain time points after infection. This additional nonspecific cytotoxic activity was presumably due to a second factor (factor X) acting in concert with IFN-gamma. Lyt-2+ cells, however, also were shown to play a role in IFN-gamma production and cytotoxicity directed against infected targets at later time points after infection. Neutralization of IFN-gamma in the samples containing cytotoxic activity abrogated the cytotoxicity against both infected and uninfected targets, but cloned murine IFN-gamma exhibited toxicity in a dose-dependent manner only against infected target cells. The data provides evidence that cytotoxicity against infected targets is due to antigen-specific induction of IFN-gamma, but other cytokine activity, most demonstrable after removal of Lyt-2.2+ cells and cytotoxic to uninfected targets, also is present.
Insights
Nude mice infected with Chlamydia trachomatis failed to produce gamma interferon (IFN-gamma). However, heterozygous mice produced IFN-gamma, which mediated cytotoxic activity against infected cells, indicating a key role for IFN-gamma in Chlamydia immunity.
Area of Science:
- Immunology
- Microbiology
Background:
- Murine Chlamydia trachomatis (MoPn) infection elicits immune responses.
- The role of specific T cell subsets and cytokines in Chlamydia pathogenesis is not fully understood.
Purpose of the Study:
- To investigate the role of T cell subsets and gamma interferon (IFN-gamma) in the immune response to MoPn infection.
- To characterize the cytotoxic mechanisms involved in controlling Chlamydia infection.
Main Methods:
- In vitro stimulation of splenocytes from infected heterozygous (nu/+) and nude (nu/nu) mice with MoPn antigen.
- Assessing cytotoxic activity against Chlamydia-infected and uninfected target cells.
- Utilizing antibody-complement lysis to deplete specific T cell populations (L3T4+ and Lyt-2+).
- Neutralization of IFN-gamma and testing the dose-dependent toxicity of cloned murine IFN-gamma.
Main Results:
- Heterozygous mice produced enhanced IFN-gamma in response to MoPn antigen, unlike nude mice.
- IFN-gamma mediated cytotoxic activity against Chlamydia-infected target cells.
- L3T4+ T cells were involved in IFN-gamma production and cytotoxicity.
- A secondary cytotoxic factor (factor X) was observed against uninfected cells, particularly after Lyt-2+ cell depletion.
- Neutralization of IFN-gamma abrogated cytotoxicity, while cloned IFN-gamma showed dose-dependent toxicity against infected targets.
Conclusions:
- Antigen-specific induction of IFN-gamma is crucial for cytotoxicity against Chlamydia-infected cells.
- Distinct cytotoxic mechanisms, including IFN-gamma-mediated and potentially other cytokine-mediated activities, operate during MoPn infection.
- Both L3T4+ and Lyt-2+ T cells play roles in the adaptive immune response to Chlamydia.