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Infection and Immunity, November 2002, p. 6319-6329, Vol. 70, No. 11
0019-9567/02/$04.00+0 DOI: 10.1128/IAI.70.11.6319-6329.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Genetics Group, Biotechnology Research Institute, National Research Council of Canada, Montreal, Quebec H4P 2R2,1 Departments of Biochemistry,2 Biology, McGill University, Montreal, Quebec H3G 1Y6, Canada3
Received 1 May 2002/ Returned for modification 26 June 2002/ Accepted 23 July 2002
Phagocytic cells such as neutrophils and macrophages are potential components of the immune defense that protects mammals against Candida albicans infection. We have tested the interaction between the mouse macrophage cell line RAW 264.7 and a variety of mutant strains of C. albicans. We used an end point dilution assay to monitor the killing of C. albicans at low multiplicities of infection (MOIs). Several mutants that show reduced virulence in mouse systemic-infection models show reduced colony formation in the presence of macrophage cells. To permit analysis of the macrophage-Candida interaction at higher MOIs, we introduced a luciferase reporter gene into wild-type and mutant Candida cells and used loss of the luminescence signal to quantify proliferation. This assay gave results similar to those for the end point dilution assay. Activation of the macrophages with mouse gamma interferon did not enhance anti-Candida activity. Continued coculture of the Candida and macrophage cells eventually led to death of the macrophages, but for the RAW 264.7 cell line this was not due to apoptotic pathways involving caspase-8 or -9 activation. In general Candida cells defective in the formation of hyphae were both less virulent in animal models and more sensitive to macrophage engulfment and growth inhibition. However the nonvirulent, hypha-defective cla4 mutant line was considerably more resistant to macrophage-mediated inhibition than the wild-type strain. Thus although mutants sensitive to engulfment are typically less virulent in systemic-infection models, sensitivity to phagocytic macrophage cells is not the unique determinant of C. albicans virulence.
National Research Council of Canada publication 44836.
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