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Recombinant murine interferon-gamma reversibly activates rat alveolar macrophages to kill Legionella pneumophila
1Medical Research Service, VA Medical Center, Seattle, WA 98108.
Abstract:
The interaction of interferon (IFN)-gamma, rat alveolar macrophages, and Legionella pneumophila was studied in vitro to define the effector cell potential of alveolar macrophages against an intracellular pathogen in a model in which the efficacy of IFN-gamma could be tested in vivo. Alveolar macrophages preincubated with IFN-gamma up-regulated Ia antigen and killed 0.5-4 logs of L. pneumophila over 4 days compared with 1-2 logs of bacterial growth in untreated cells. The bactericidal effect was dose dependent, evident over a wide range of bacterial inocula, and not suppressed by hydrocortisone. Preincubation with IFN-gamma was unnecessary and insufficient, as intracellular replication was reversed by exposure to IFN-gamma up to 48 h after infection, and neutralization of IFN-gamma after infection permitted bacterial growth. IFN-gamma thus converts alveolar macrophages from target cells to effector cells in host defense against L. pneumophila and may be of therapeutic benefit in legionellosis.
Insights
Interferon-gamma (IFN-γ) enhances alveolar macrophages to kill the intracellular pathogen Legionella pneumophila. This immune response shows therapeutic potential for treating legionellosis.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Alveolar macrophages are crucial for lung immunity.
- Legionella pneumophila is an intracellular pathogen causing pneumonia.
- Interferon-gamma (IFN-γ) is a key immune signaling molecule.
Purpose of the Study:
- To investigate the role of IFN-γ in activating rat alveolar macrophages against L. pneumophila.
- To determine the potential of IFN-γ as a therapeutic agent for legionellosis.
Main Methods:
- In vitro study of rat alveolar macrophages and L. pneumophila.
- Treatment with IFN-γ at various time points and doses.
- Assessment of macrophage Ia antigen expression and bacterial killing capacity.
Main Results:
- IFN-γ up-regulated Ia antigen expression on macrophages.
- IFN-γ-treated macrophages killed 0.5-4 logs of L. pneumophila, while untreated cells showed bacterial growth.
- Bactericidal effect was dose-dependent and effective even when IFN-γ was administered post-infection.
Conclusions:
- IFN-γ transforms alveolar macrophages into effective effector cells against L. pneumophila.
- IFN-γ demonstrates significant therapeutic potential for treating legionellosis.