From secretome analysis to immunology: chitosan induces major alterations in the activation of dendritic cells via a TLR4-dependent mechanism

TL;DR

This study reveals that chitosan activates dendritic cells through a TLR4-dependent pathway, upregulating membrane markers but not cytokine production, and modulating cytokine balance upon sequential stimulation, impacting immune response regulation.

Contribution

It demonstrates that chitosan induces partial activation of dendritic cells via TLR4, affecting membrane markers and cytokine balance without stimulating cytokine secretion, a novel insight into immune modulation by fungal components.

Findings

Chitosan upregulates MHC II, CD80, CD86 on dendritic cells.

Chitosan activates dendritic cells via TLR4 without cytokine production.

Sequential stimulation alters IL-12/IL-10 cytokine balance.

Abstract

Dendritic cells are known to be activated by a wide range of microbial products, leading to cytokine production and increased levels of membrane markers such as major histocompatibility complex class II molecules. Such activated dendritic cells possess the capacity to activate na\"ive T cells. In the present study we demonstrated that immature dendritic cells secrete both the YM1 lectin and lipocalin-2. By testing the ligands of these two proteins, chitosan and siderophores, respectively, we also demonstrated that chitosan, a degradation product of various fungal and protozoal cell walls, induces an activation of dendritic cells at the membrane level, as shown by the up-regulation of membrane proteins such as class II molecules, CD80 and CD86 via a TLR4-dependent mechanism, but is not able to induce cytokine production. This led to the production of activated dendritic cells unable to stimulate T cells. However, costimulation with other microbial products overcame this partial activation and restored the capacity of these activated dendritic cells to stimulate T cells. In addition, successive stimulation with chitosan and then by lipopolysaccharide induced a dose-dependent change in the cytokinic IL-12/IL-10 balance produced by the dendritic cells.