CLINICAL MICROBIOLOGY REVIEWS, Oct. 1996, p. 469–488 Vol. 9, No. 4 0893-8512/96/$04.0010 Copyright q 1996, American Society for Microbiology Virulence Factors of Medically Important Fungi LAURA H. HOGAN, 1 * BRUCE S. KLEIN, 1,2,3 AND STUART M. LEVITZ 4 Departments of Pediatrics, 1 Internal Medicine, 2 and Medical Microbiology and Immunology, 3 University of Wisconsin Medical School and University of Wisconsin Hospitals and Clinics, Madison, Wisconsin 53792, and Division of Infectious Diseases, Evans Memorial Department of Clinical Research, and Department of Medicine, The University Hospital, Boston University Medical Center, Boston, Massachusetts 02118 4 INTRODUCTION .......................................................................................................................................................469 FUNGAL PATHOGENS ............................................................................................................................................471 Aspergillus Species ...................................................................................................................................................471 Introduction .........................................................................................................................................................471 Proteases ..............................................................................................................................................................471 Host defense factors ...........................................................................................................................................472 Toxins ...................................................................................................................................................................472 Miscellaneous factors .........................................................................................................................................473 Blastomyces dermatitidis ..........................................................................................................................................473 Cell wall fractions ...............................................................................................................................................473 a-1,3-Glucan ........................................................................................................................................................473 WI-1 adhesin/antigen..........................................................................................................................................474 African blastomycosis .........................................................................................................................................474 Coccidioides immitis .................................................................................................................................................474 Extracellular proteinases ...................................................................................................................................475 Estrogen-binding proteins .................................................................................................................................475 Cryptococcus neoformans .........................................................................................................................................475 Introduction .........................................................................................................................................................475 Capsule .................................................................................................................................................................476 Phenoloxidase ......................................................................................................................................................476 Varietal differences and mating types ..............................................................................................................477 Miscellaneous factors .........................................................................................................................................477 Dematiaceous Fungi ...............................................................................................................................................478 Histoplasma capsulatum...........................................................................................................................................478 Avirulent mutants ...............................................................................................................................................478 Intracellular growth............................................................................................................................................478 Thermotolerance .................................................................................................................................................479 Agents of Mucormycosis ........................................................................................................................................479 Paracoccidioides brasiliensis ....................................................................................................................................479 Estrogen-binding proteins .................................................................................................................................479 Cell wall components..........................................................................................................................................480 Laminin binding..................................................................................................................................................480 Sporothrix schenckii .................................................................................................................................................481 Thermotolerance .................................................................................................................................................481 Extracellular enzymes ........................................................................................................................................481 CONCLUSIONS .........................................................................................................................................................482 ACKNOWLEDGMENTS ...........................................................................................................................................482 REFERENCES ............................................................................................................................................................482 INTRODUCTION Central to a review of virulence factors is the question, “What is a virulence factor?” Strictly and simply defined, it is any factor that a fungus possesses that increases its virulence in the host. Many virulence factors are of such obvious impor- tance that they are often taken for granted. For example, the ability of a fungus to grow at 378C and physiological pH is a virulence factor for fungi that invade deep tissues and the transition to a parasitic form is essential for the pathogenicity of the dimorphic fungi. Moreover, a size compatible with al- veolar deposition is a virulence factor for fungi acquired by inhalation of airborne spores. This review will concentrate on the virulence factors that allow fungi to elude specific aspects of host defenses (Table 1). Virulence factors that affect fungal pathogenicity in nonmammalian hosts (e.g., plant species) will not be discussed. There is strong molecular evidence that Pneumocystic carinii is a fungus (154), but both P. carinii and Candida species have been the subject of several excellent reviews (29–32, 58, 59, 113, 196, 224, 286) and will not be considered in this review. The ideal test of a virulence factor is to compare biological responses in fungi with and without the factor. Such compar- isons have traditionally required the isolation of mutant strains * Corresponding author. Mailing address: Room K4/443, Clinical Science Center, 600 Highland Ave., Madison, WI 53792. Phone: (608) 263-6203. Fax: (608) 263-0440. Electronic mail address: lhhogan @facstaff.wisc.edu. 469 Downloaded from https://journals.asm.org/journal/cmr on 25 July 2023 by 171.243.71.223.
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