Evidence that Members of the Secretory Aspartyl Proteinase Gene Family, in Particular SAP2, Are Virulence Factors for Candida Vaginitis

Virulence of Candida albicans strains with targeted disruption of secretory aspartyl proteinase genes (SAP1 to SAP6) was assessed in an estrogen-dependent rat vaginitis model. Null sap1 to sap3 but not sap4 to sap6 mutants lost most of the virulence of their parental strain SC5314. In particular, the sap2 mutant was almost avirulent in this model. Reinsertion of the SAP2 gene into this latter mutant led to the to recovery of the vaginopathic potential. The vaginal fluids of the animals infected by the wild type strain or by the sap1 or sap3 mutants expressed a pepstatin-sensitive proteinase activity in vitro. No traces of this activity were found in the vaginal fluid of rats challenged by the sap2 mutant. All strains were capable of developing true hyphae during infection. Thus, members of SAP family, in particular SAP2, play a clear pathogenic role in vaginitis and may constitute a novel target for chemoimmunotherapy of this infection. Infections caused by Candida albicans and a few other related species have increased in prevalence worldwide [1, 2]. They range from mucosal diseases, almost invariably observed in AIDS patients, to fatal systemic episodes in severely neutropenic subjects [3‐5]. The wide spectrum of candidiasis and their clinical importance has stimulated renewed interest in understanding the mechanisms of Candida pathogenicity, but despite intense efforts, no clear-cut evidence for true virulence factors has been found in this fungus. Several traits have been advocated as putatively important aspects of fungal attack to the host [6], but the relevant studies have mostly been descriptive and often limited to merely correlative aspects. Moreover, these studies have seldom addressed the problem of which virulence traits come into play in the different candidal diseases (e.g., mucosal vs. systemic forms). Among the putative virulence factors of C. albicans, the most pathogenic organism of this genus [1], the secretory aspartyl proteinases (Sap) occupy a special position because of their molecular characterization and preliminary, largely circumstantial evidence about their role in experimental and clinical candidiasis [7‐13]. Sap constitute a family of isoenzymes encoded by at least nine genes (SAP) that are differentially expressed in vitro and in vivo [14‐19]. These enzymes are able to