Human thioredoxin, a damage-associated molecular pattern and Malassezia-crossreactive autoallergen, modulates immune responses via the C-type lectin receptors Dectin-1 and Dectin-2

L M Roesner,P Kienlin,B Lepenies,G Begemann,M K Raulf,M Ernst,W Chen,T Werfel

doi:10.1038/s41598-019-47769-2

Abstract

Human thioredoxin (hTrx), which can be secreted from cells upon stress, functions in allergic skin inflammation as a T cell antigen due to homology and cross-reactivity with the fungal allergen Mala s13 of the skin-colonizing yeast Malassezia sympodialis. Recent studies have shown that cell wall polysaccharides of Malassezia are detected by the immune system via the C-type lectin receptors Dectin-1 and Dectin-2, which are expressed on myeloid cells. Therefore, this study aimed to investigate a putative interaction between Dectin-1, Dectin-2 and the allergens Mala s13 and hTrx. Stimulation of human monocyte-derived dendritic cells or macrophages with Mala s13 or hTrx resulted in remarkable secretion of IL-1β and IL-23. Blocking experiments suggest that hTrx induces IL-23 by Dectin-1 binding and IL-1β by binding to either Dectin-1 or Dectin-2. Regarding Mala s13, Dectin-1 appears to be involved in IL-1β signaling. Interference of Syk kinase function was performed to investigate downstream signaling, which led to diminished hTrx responses. In our experiments, we observed rapid internalization of Mala s13 and hTrx upon cell contact and we were able to confirm direct interaction with Dectin-1 as well as Dectin-2 applying a fusion protein screening platform. We hypothesize that this cytokine response may result in a Th2/Th17-polarizing milieu, which may play a key role during the allergic sensitization in the skin, where allergen presentation to T cells is accompanied by microbial colonization and skin inflammation.

Highlights

Autoimmunity and allergy represent two examples of an aberrant reaction of the immune system, where immune responses are mounted against harmless self or environmental antigens
Recent studies have shown that Malassezia PAMPs are recognized by Dectin-1 and Dectin-2, members of the pattern recognition receptor (PRR) family of C-type lectin receptors (CTLR), leading to NLRP3 inflammasome activation and IL-1β production[7,8]
Both cell types released considerable amounts of IL-1β and IL-23 in response to both proteins as well as to hot alkali-treated Zymosan (Zymosan depleted), a S. cerevisae-cell wall preparation that is described as a specific ligand of Dectin-1 but not of toll-like receptors (TLR) (Fig. 1A,C)

Summary

Introduction

Autoimmunity and allergy represent two examples of an aberrant reaction of the immune system, where immune responses are mounted against harmless self or environmental antigens. It is believed that danger signals are present under such circumstances, which influence the antigen presenting cells (APC) towards a pro-inflammatory phenotype, leading to the generation of specific pro-inflammatory T cells. This break of tolerance is regarded as a key point in the development of autoimmunity and allergy. We and others showed in the past, that a genetically highly conserved human paralogue of the Malassezia allergen Mala s13, namely thioredoxin (hTrx) acts as a DAMP on the immune system and is released upon stress from skin cells[13,14,15,16]. To investigate whether Malassezia PAMPs and related human DAMPs may be ligands for CTLR, we performed specific binding and blocking experiments on monocyte-derived dendritic cells and macrophages as model APCs in vitro

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