Elucidating the immunopathogenesis of vulvovaginal candidiasis using an organ-on-chip model

Vulvovaginal candidiasis (VVC) is one of the principal infectious causes of vaginal and vulvar inflammation. Approximately 75% of women suffer from this infection at least once during their reproductive years, and a subgroup suffers from recurrent infections that dramatically impact quality of life. A hyperinflammatory innate immune response associated with excessive neutrophil recruitment drives symptoms of VVC. Current models such as classical in vitro cell culture and mice models cannot completely mimic human VVC for the absence of a physiological tissue environment and intrinsic pathophysiological differences. Conversely, organ-on-chip models provide a closer look at human physiology with higher capacity to control microenvironment as well as tissue-specific functions due to their design. The recent technological advances in microfluidics and organ-on-chip systems paved the way to establish a VVC-on-chip model. We therefore established a novel VVC-on-chip model consisting of an epithelial and a vascular compartment to dissect the complex host-pathogen interplay of VVC in a more human context. A-431 vaginal epithelial cells co-cultured with human monocyte-derived macrophages, and human umbilical vein vascular cells were contained in the two cavities, respectively. Primary human neutrophils were perfused in the vascular compartment to study the immunopathology during Candida infections. The flexibility of this model enables real-time monitoring and easy manipulations, for instance, immunofluorescence staining can be performed to visualize infection of the vaginal epithelial cells in situ while immunopathogenesis can be evaluated through lactate dehydrogenase release and quantification of neutrophil activation markers. Consistent with what is known about the immunopathogenesis of VVC, our model demonstrated that perfused neutrophils from the vascular cavity migrated to the infected epithelium, promoting higher vaginal epithelial cell damage and IL-8 release during C. albicans infection. Collectively, this VVC-on-chip model possesses potential to illuminate molecular mechanisms underlying the over-aggressive immune responses to the vaginal Candida infection.