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Differing requirement for inducible nitric oxide synthase activity in clearance of primary and secondary Cryptococcus
1Trudeau Institute, Saranac Lake, NY 12983, USA. kaguirre@clarkson.edu
Abstract:
The role of nitric oxide in resistance to cryptococcal infection was investigated. Mice deficient in inducible nitric oxide synthase (INOS) did not survive a primary intratracheal infection as did INOS-replete control mice. Despite adequate recruitment of host cells and generation of interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha at the site of infection, INOS-deficient mice failed to clear yeast from their lungs by five weeks of infection, in contrast to wild-type mice. INOS-deficient mice also had higher yeast brain burdens than did control mice after a primary intracerebral infection. Therefore, generation of nitric oxide is required for resistance to primary cryptococcal infection. However, INOS-deficient mice vaccinated subcutaneously and rechallenged intravenously had lung and brain yeast burdens equivalent to those of vaccinated controls, and therefore expressed effective acquired immunity to Cryptococcus neoformans. Cells harvested from infected INOS-deficient mice by bronchoalveolar lavage acted as anti-cryptococcal effectors in vitro at an effector:target ratio of 100:1, provided IFN-gamma was present, but did not inhibit yeast proliferation at a 10:1 effector:target ratio as cells from wild-type mice did. Therefore, INOS activity is important for anti-cryptococcal function of effectors of immunity during the primary response, but not for the generation or expression of secondary immunity to C. neoformans.
Insights
Nitric oxide, generated by inducible nitric oxide synthase (iNOS), is crucial for controlling primary cryptococcal infections. While essential for the initial immune response, iNOS is not required for developing acquired immunity to Cryptococcus neoformans.
Area of Science:
- Immunology
- Infectious Diseases
- Microbiology
Background:
- Cryptococcus neoformans is an opportunistic fungal pathogen causing life-threatening infections, particularly in immunocompromised individuals.
- Nitric oxide (NO) is a signaling molecule with diverse roles in immunity, including antimicrobial functions.
Purpose of the Study:
- To investigate the role of inducible nitric oxide synthase (iNOS)-derived nitric oxide in host resistance to primary and secondary Cryptococcus neoformans infection.
- To determine if iNOS activity is essential for the generation and effector functions of acquired immunity.
Main Methods:
- Comparison of survival and fungal burden in iNOS-deficient and wild-type mice following primary intratracheal or intracerebral C. neoformans infection.
- Assessment of acquired immunity by evaluating fungal burden in vaccinated and challenged iNOS-deficient and wild-type mice.
- In vitro analysis of anti-cryptococcal effector cell function from bronchoalveolar lavage fluid.
Main Results:
- iNOS-deficient mice exhibited increased susceptibility and mortality during primary infection, failing to clear yeast from lungs and showing higher brain fungal burdens.
- Despite impaired primary response, iNOS-deficient mice developed effective acquired immunity upon vaccination and rechallenge, with comparable lung and brain fungal burdens to controls.
- Immune effector cells from iNOS-deficient mice demonstrated reduced in vitro anti-cryptococcal activity at lower effector:target ratios, highlighting the importance of NO in the primary response.
Conclusions:
- Nitric oxide generation via iNOS is essential for effective host defense during the primary phase of cryptococcal infection.
- iNOS activity is critical for the anti-fungal function of immune effector cells in the initial immune response.
- The development and expression of secondary immunity to C. neoformans are independent of iNOS activity.