Defective IL-17- and IL-22-dependent mucosal host response to Candida albicans determines susceptibility to oral candidiasis in mice expressing the HIV-1 transgene

Abstract

Background: The tissue-signaling cytokines IL-17 and IL-22 are critical to host defense against oral Candida albicans infection, by their induction of oral antimicrobial peptide expression and recruitment of neutrophils. Mucosal Th17 cells which produce these cytokines are preferentially depleted in HIV-infected patients. Here, we tested the hypothesis that defective IL-17- and IL-22-dependent host responses to C. albicans determine the phenotype of susceptibility to oropharyngeal candidiasis (OPC) in transgenic (Tg) mice expressing HIV-1.

Results: Naïve CD4+ T-cells and the differentiated Th1, Th2, Th17, Th1Th17 and Treg lineages were all profoundly depleted in cervical lymph nodes (CLNs) of these Tg mice. However, naive CD4+ cells from Tg mice maintained the capacity to differentiate into these lineages in response to polarizing cytokines in vitro. Expression of Il17, Il22, S100a8 and Ccl20 was enhanced in oral mucosal tissue of non-Tg, but not of Tg mice, after oral infection with C. albicans. Treatment of infected Tg mice with the combination of IL-17 and IL-22, but not IL-17 or Il-22 alone, significantly reduced oral burdens of C. albicans and abundance of Candida hyphae in the epithelium of tongues of infected Tg mice, and restored the ability of the Tg mice to up-regulate expression of S100a8 and Ccl20 in response to C. albicans infection.

Conclusions: These findings demonstrate that defective IL-17- and IL-22-dependent induction of innate mucosal immunity to C. albicans is central to the phenotype of susceptibility to OPC in these HIV transgenic mice.

Figure 1

Immunophenotypes of cervical lymph node CD4+ T-cell subsets in CD4C/HIV ^MutA Tg and non-Tg control mice. CLNs were harvested 7 or 70 days after oral infection or not with Candida albicans. Data are expressed as (A) the percentage of CD4+ T-cells or as (B) absolute numbers of cells, and are the mean ± SD of 4 to 13 independent experiments. *, greater (p < 0.05) than non-Tg mice; **, lower (p < 0.05) than non-Tg mice; ***, greater (p < 0.05) than uninfected non-Tg mice.

Figure 2

qRT-PCR analysis of signature genes of CD4+ T-cell subsets polarized in vitro . Naive CD4+ precursors were harvested from CD4C/HIV^MutA Tg and non-Tg mice, and incubated with subset-specific differentiating cytokines and blocking antibodies. Bars represent the mean ± standard error range of significantly (p < 0.05) up- or down-regulated genes compared to that of control naive cells from non-Tg mice, incubated without cytokines and antibodies. In all differentiating conditions, gene expression of IL-4 and IL-10 was not significantly different (p > 0.05) from control. Data are from 6 independent experiments.

Figure 3

Cytokine production in supernatants of CD4+ T-cell subsets polarized in vitro . Naive CD4+ precursors were harvested from CD4C/HIV^MutA Tg and non-Tg mice, and incubated with (Th1, Th2, Th17, Treg) or without (control) subset-specific differentiating cytokines and blocking antibodies. *, significantly greater (p < 0.05) than the other subsets and control; **, significantly lower (P < 0.05) than the other subsets and control; ***, significantly lower (p < 0.05) than control. In all differentiating conditions, production of IL-1β and IL-6 was undetectable. Data are mean ± SD of 6 independent experiments.

Figure 4

Oral burdens of C. albicans strain LAM-1 in CD4C/HIV ^MutA Tg mice and non-Tg control mice. Tg mice were treated or not with the combination of IL-17 and IL-22 (A) or with IL-17 or IL-22 alone (B, C). *, p < 0.05 control Tg vs. control non-Tg; **, p < 0.05 treated Tg vs. control Tg; ***, p < 0.05 treated Tg vs. control non-Tg. Data are the means ± SD of results from 10 to 22 mice per group.

Figure 5

Histopathology of tongues from CD4C/HIV ^MutA Tg and non-Tg mice. Tg mice were treated (A1, A2) or not (B1, B2) with the combination of IL-17 and IL-22 on days 1, 3 and 5 after oral inoculation with C. albicans, and assessed on day 7. Control non-Tg mice were infected with C. albicans and untreated (C1, C2). Inflammatory cells are denoted by black arrows. Tissues were stained with hematoxylin phloxine saffron (HPS) or Gomori-Grocott methenamine silver. Images are representative of 6 mice per group with consistent results.

Figure 6

Expression levels of Defb3 , S100a8, Ccl20, Il17 and Il22 genes in tongue tissue. Tg mice were treated or not with the combination of IL-17 and IL-22 on days 1, 3 and 5 after oral inoculation with C. albicans, and RNA was extracted from tongue tissue on day 7. Ccl2 did not display significant differences of expression under any of the experimental conditions (data not shown). Bars represent the mean ± standard error range of significantly (p < 0.05) up-regulated genes, compared to control uninfected non-Tg mice. Data are from 5 mice.