Fungal Morphogenetic Pathways Are Required for the Hallmark Inflammatory Response during Candida albicans Vaginitis

Abstract

cVulvovaginal candidiasis, caused primarily by Candida albicans, presents significant health issues for women of childbearing age. As a polymorphic fungus, the ability of C. albicans to switch between yeast and hyphal morphologies is considered its central virulence attribute. Armed with new criteria for defining vaginitis immunopathology, the purpose of this study was to determine whether the yeast-to-hypha transition is required for the hallmark inflammatory responses previously characterized during murine vaginitis. Kinetic analyses of vaginal infection with C. albicans in C57BL/6 mice demonstrated that fungal burdens remained constant throughout the observation period, while polymorphonuclear leukocyte (PMN), S100A8, and interleukin-1␤ levels obtained from vaginal lavage fluid increased by day 3 onward. Lactate dehydrogenase activity was also positively correlated with increased effectors of innate immunity. Additionally, immunodepletion of neutrophils in infected mice confirmed a nonprotective role for PMNs during vaginitis. Determination of the importance of fungal morphogenesis during vaginitis was addressed with a two-pronged approach. Intravaginal inoculation of mice with C. albicans strains deleted for key transcriptional regulators (bcr1⌬/⌬, efg1⌬/⌬, cph1⌬/⌬, and efg1⌬/⌬ cph1⌬/⌬) controlling the yeast-to-hypha switch revealed a crucial role for morphogenetic signaling through the Efg1 and, to a lesser extent, the Bcr1 pathways in contributing to vaginitis immunopathology. Furthermore, overexpression of transcription factors NRG1 and UME6, to maintain yeast and hyphal morphologies, respectively, confirmed the importance of morphogenesis in generating innate immune responses in vivo. These results highlight the yeast-to-hypha switch and the associated morphogenetic response as important virulence components for the immunopathogenesis of Candida vaginitis, with implications for transition from benign colonization to symptomatic infection. Candida albicans, an opportunistic polymorphic fungal species, is the leading cause of vulvovaginal candidiasis (VVC) and presents major quality-of-life issues for women worldwide (1). VVC is characterized by itching, burning, and redness of the vulva and vaginal mucosa, often accompanied by a thick white vaginal discharge. It is estimated that 75% of all women will experience an episode of VVC at least once in their lifetime. Major risk factors for development of acute vaginitis include the use of high-estrogen oral contraceptives, hormone replacement therapy, and uncontrolled diabetes mellitus (1). A smaller subset of women (5 to 8%) experience recurrent VVC (RVVC), defined as having 3 or more major vaginitis incidents per year. These chronic bouts of vaginal inflammation are idiopathic in nature, having no clinically recognizable predisposition for infection (2).Despite its widespread prevalence, relatively little is known about the protective immune mechanisms involved in defense against vaginal candidiasis. It was long believed that women with RVVC harbored defects...

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