To investigate the involvement of ICAM-1 in the adhesion of Candida to the genitourinary epithelial cells in high glucose, we examined the adhesion of Candida albicans or Candida glabrata to human vaginal epithelial cells (VK2/E6E7) or human vulvovaginal epidermal cells (A431). These cells were cultured in 100, 500 or 3000 mg/dL glucose for three days and inoculated with Candida for 60 minutes. Followed by, adhering of Candida to the cells, which were counted. While the adhesion of Candida albicans to VK2/E6E7 significantly increased in the high glucose, A431 did not. We next examined the expression of ICAM-1 as a ligand on the epithelial cells. ICAM-1 expression was increased in VK2/E6E7 cultured in the high glucose; however, the expression level in A431 was not high compared with VK2/E6E7. This data suggested that ICAM-1 functions as one of ligands in the adhesion of Candida albicans to the vaginal epithelial cells in a high glucose environment. Impact statement What is already known on the subject: Candida's complement receptor is involved in the adhesion to epithelial cells. The expression of this receptor has been reported to increase as glucose concentration increases. This is considered as a contributing factor to the high risk for vulvovaginal candidiasis (VVC) in diabetes. On the host side, diabetic patients have a factor that facilitates adhesion of Candida to epithelial cells. This factor has been unknown until recently. What the results of this study add: In this study, we used a vaginal epithelial cell line and showed that the adhesion of C. albicans to cells increased at higher glucose concentrations. At the same time, ICAM-1 expression of cells also increased. Thereby, it is suggested that the expression of ICAM-1 in vaginal epithelial cells is increased by glucose such as urinary sugar in diabetic patients and is a condition for facilitating adhesion of Candida. What the implications are of these findings for clinical practice and/or further research: We expect not only host immune dysfunction but also alteration in epithelial cells will be focussed on as a cause of VVC in diabetic patients.
Keywords: Candida adhesion; Diabetes; ICAM-1; complement receptor; high glucose; vaginal epithelial cells.