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Interferon-gamma activates rat alveolar macrophages for anticryptococcal activity
C H Mody1, C L Tyler, R G Sitrin
1Department of Internal Medicine, University of Calgary, Alberta, Canada.
Abstract:
Cryptococcus neoformans is a pathogenic yeast causing disease predominantly in immunosuppressed patients. C. neoformans is acquired by the pulmonary route, where the alveolar macrophage (AM) is a resident mechanism of host defense. The ability of rat AM to be activated by products of the immune response for enhanced anticryptococcal effect has not previously been demonstrated. Rat AM could be activated in vitro for anticryptococcal activity by medium conditioned by concanavalin A-stimulated splenic lymphocytes. A monoclonal antibody that neutralizes interferon-gamma (IFN-gamma) inhibited the macrophage-activating activity of lymphokine-containing medium (LCM). Further, recombinant IFN-gamma activated AM for anticryptococcal activity. The concentration of IFN-gamma in LCM, determined by enzyme-linked immunosorbent assay, was equivalent to the range of concentrations of recombinant IFN-gamma which activated AM. Thus, IFN-gamma was necessary and sufficient for optimal macrophage activation by medium conditioned by proliferating lymphocytes. Lipopolysaccharide could not enhance the anticryptococcal activity produced by optimal concentrations of LCM or IFN-gamma but did augment the effects of submaximal stimulation. Both LCM and recombinant IFN-gamma increased the percentage of macrophages with cell-associated cryptococcus, suggesting that activation of AM enhanced the adhesion or uptake of cryptococcus. We speculate that inadequate availability of lymphokines such as IFN-gamma may result in the immunodeficient state in hosts unable to generate an appropriate response to cryptococcal antigens. Administration of lymphokines such as IFN-gamma to immunosuppressed hosts might circumvent the defect in cell-mediated immunity.
Insights
Interferon-gamma (IFN-gamma) activates rat alveolar macrophages (AM) to fight the yeast Cryptococcus neoformans. This immune response is crucial for host defense against fungal infections, especially in immunocompromised individuals.
Area of Science:
- Immunology
- Mycology
- Cell Biology
Background:
- Cryptococcus neoformans is a yeast pathogen primarily affecting immunosuppressed individuals.
- Alveolar macrophages (AM) are key pulmonary immune cells defending against C. neoformans.
- The activation of rat AM for enhanced anticryptococcal activity by immune products was previously uncharacterized.
Purpose of the Study:
- To investigate the in vitro activation of rat AM for enhanced anticryptococcal activity.
- To determine the role of interferon-gamma (IFN-gamma) in this activation process.
- To explore the potential therapeutic implications of lymphokine administration in cryptococcal infections.
Main Methods:
- Rat AM were incubated with medium conditioned by concanavalin A-stimulated splenic lymphocytes.
- Monoclonal antibodies neutralizing IFN-gamma were used to assess its role.
- Recombinant IFN-gamma and lipopolysaccharide were applied to evaluate their effects on AM activity.
- Enzyme-linked immunosorbent assay (ELISA) quantified IFN-gamma levels.
Main Results:
- Lymphokine-conditioned medium (LCM) activated rat AM for anticryptococcal activity.
- IFN-gamma was identified as necessary and sufficient for LCM-induced AM activation.
- Recombinant IFN-gamma mimicked the activating effects of LCM.
- Both LCM and IFN-gamma enhanced macrophage association with C. neoformans.
Conclusions:
- IFN-gamma is a critical mediator for activating alveolar macrophages against Cryptococcus neoformans.
- Deficiencies in IFN-gamma production may contribute to susceptibility in immunosuppressed hosts.
- Therapeutic administration of IFN-gamma could potentially enhance cell-mediated immunity against fungal infections.