IL-12 secretion by Langerhans cells stimulated with Candida skin test reagent is mediated by dectin-1 in some healthy individuals

Abstract

Objective: Our group and others have shown that serial intra-lesional injections of common warts with skin testing reagents such as Candida, mumps and Trichophyton are effective in regressing injected and non-injected warts. Anti-HPV T-cell responses appear to be induced. The goal of this study was to understand the mechanisms of how Candida skin testing reagent enhances immune responses.

Methods: The following immunological features were studied to understand how Candida induces immune responses in healthy subjects: (1) proliferative capacity of T-cells upon exposure to Candida through monocyte-derived human Langerhans cells (LCs) measured using alamarBlue, (2) cytokine (IL-1β, IL-6, IL-8, IL-10, IL-12p40, IL-23Ap19, IFN-γ, and TNF- expression upon Candida stimulation of LCs by quantitative reverse transcription (qRT)-PCR and cytokine secretion by ELISA, (3) expression of pattern recognition receptors (PRRs) known to associate with Candida albicans (DC-SIGN, dectin-1, dectin-2, galectin-3, mincle, mannose receptor, Toll-like receptors 1, 2, 4, 6, and 9) on LCs by qRT-PCR, (4) role of dectin-1 in IL-12 production by antibody blocking, and (5) induction of Th1, Th2, and/or Th17 responses by intracellular cytokine staining of CD4 cells exposed to Candida pulsed LCs for IFN-γ, IL-4, and IL-17A.

Results: T-cell proliferation upon stimulation with Candida-pulsed LCs was significantly higher compared to proliferation in the absence of Candida (p=0.004). The most frequently expressed cytokine in stimulated LCs was IL-12p40 mRNA, and IL-12p40 and IL-12p70 were also detected at protein levels. All other cytokine mRNAs examined were detected in the following order of decreasing frequency: IL23Ap19, IFN-γ, IL-1β, IL-6, IL-8, and IL-10. LCs expressed all PRRs examined. Anti-dectin-1 inhibited IL-12p40 mRNA production upon Candida stimulation of LCs from some healthy subjects. IFN-γ secretion was increased and IL-4 secretion was decreased in CD4 cells of a few healthy subjects, but IL-17A was essentially unchanged upon Candida treatment.

Conclusions: Proliferation of T-cells in a substantial majority of healthy subjects can be demonstrated with Candida stimulation. We show Th1 promotion and dectin-1 stimulation of LCs as potential mechanisms in some healthy subjects.

Keywords: Candida; Dectin-1; Interleukin-12; T-cell; Th1.