Abstract: 【Abstract】 Objective To analyze functional changes in macrophages in mouse models of vulvovaginal candidiasis （VVC） by modulating indoleamine 2,3-dioxygenase 1 （IDO1）. Methods Forty specific-pathogen-free female ICR mice were randomly divided into 4 groups using a complete randomization method: a blank group, a VVC model group, a VVC model + 1-methyltryptophan （1-MT） group （referred to as the 1-MT group）, a VVC model + interferon-γ （IFN-γ） group （referred to as the IFN-γ group）, with 10 mice in each group. Except for the blank group, all the mice were injected subcutaneously with estradiol benzoate oil solution in the abdomen every other day for 6 days prior to modeling to induce pseudoestrus; after successful induction of pseudoestrus, the mice were inoculated vaginally with Candida albicans suspensions at a concentration of 2 × 109 CFU/ml once a day for 5 days to establish VVC mouse models, and subcutaneous injections of estradiol benzoate oil solution were continued simultaneously to maintain the pseudoestrus state; 1 day before inoculation with fungal suspensions, mice in the 1-MT group and IFN-γ group were pretreated with 1-MT and IFN-γ respectively, followed by once-daily same intervention for 6 consecutive days; mice in the blank group and VVC model group were intraperitoneally injected with physiological saline solution once a day for 6 consecutive days. On the 5th day of modeling, vaginal conditions in mice were observed and vaginal symptoms were scored; the vaginal lavage fluid was collected for smear microscopy and fungal colony counting; then, the mice were sacrificed, the vaginal tissues were collected and subjected to hematoxylin-eosin （HE） staining and periodic acid-Schiff （PAS） staining, and the expression of IDO1 and the macrophage surface marker F4/80 was determined in the vaginal tissues by an immunofluorescence method; real-time fluorescence-based quantitative PCR （qPCR） was performed to determine mRNA expression levels of IDO1, inducible nitric oxide synthase （iNOS）, and arginase 1 （Arg-1） in the vaginal tissues, and Western blot analysis to determine the IDO1 protein expression in the vaginal tissues. One-way analysis of variance was used to analyze the differences in indices among groups, and Tukey test was used for multiple comparisons. Results Smear microscopic examination of the vaginal lavage fluid on the 5th day of modeling showed elongated hyphae with a few spores in the VVC model group, a large number of elongated hyphae aggregating in clusters with surrounding spores in the 1-MT group, and a few thin and short hyphae with a large number of spores in the IFN-γ group. Compared with the VVC model group （360.0 ± 15.9）, the fungal colony counts in the vaginal lavage fluid significantly increased in the 1-MT group （523.7 ± 67.7, P = 0.002）, but significantly decreased in the IFN-γ group （258.3 ± 27.57, P = 0.026）. HE staining and PAS staining showed small abscess formation in the epidermis and predominant infiltration of neutrophils throughout the epidermal and dermal layers with a large number of spores and a few hyphae in the VVC model group; thickened epidermis and diffuse inflammatory infiltration predominated by neutrophils in the dermis were seen in the 1-MT group, with a large number of hyphae and spores aggregating into clusters, which were predominated by hyphae; in the IFN-γ group, spores aggregated in the epidermis without obvious hyphae, and a small amount of inflammatory cells predominated by neutrophils infiltrated the dermis. Immunofluorescence assay revealed that the relative fluorescence intensities of IDO1 and F4/80 were highest in the IFN-γ group and the 1-MT group, respectively. Western blot analysis revealed that the IDO1 protein expression in the VVC model group was significantly higher than that in the blank group （P < 0.001） and the 1-MT group （P < 0.05）, but significantly lower than that in the IFN-γ group （P < 0.05）. qPCR showed that iNOS mRNA expression significantly increased in the VVC model group compared with the blank group （P < 0.01）, and increased in the IFN-γ group compared with the blank group, VVC model group and 1-MT group （all P < 0.001）; Arg-1 mRNA expression significantly increased in the VVC model group compared with the blank group （P < 0.001） and IFN-γ group （P < 0.01）, and increased in the 1-MT group compared with the blank group, VVC model group, and IFN-γ group （all P < 0.001）. Conclusion In the VVC mouse models, upregulation of IDO1 may cause macrophage polarization toward the M1 phenotype, and inhibition of IDO1 may cause increased macrophage recruitment and exacerbate the inflammatory response.

Key words: Candida albicans, Candidiasis, vulvovaginal, Macrophages, IDO1, Host immunity