Molecular and Genetic Medicine

Uptake of Chitosan-Based Viscoelastic Hydrogel Particles by Antigen Presenting Cells and Activation of Innate Immune Responses

Abstract

Jonas Binnmyr, Marie Olliver, Theresa Neimert-Andersson, Sara Heidenvall, Vladana Vukojević, Hans Grönlund and Guro Gafvelin

The chitin-derived biopolymer chitosan has been shown to possess immunostimulatory properties in several systems and has rendered interest as a candidate adjuvant in vaccine formulations. The mechanisms underlying this effect are not completely understood at the cellular and molecular level, but activation of inflammasome and caspase-1 in antigen presenting cells (APC) was recently suggested to be vital for immune activation. In this study, chitosan-based viscoelastic hydrogel particles of two sizes, 10 μm and 200 μm, were evaluated in regard to cellular uptake and activation of APCs. Macrophages derived from the human cell line THP-1 were shown by flow cytometry and confocal laser scanning microscopy to take up FITC-labelled chitosan particles of both sizes via an active process that could be inhibited by cytochalasin D. To investigate if the viscoelastic chitosan particles cause inflammasome activation, NFκB and IL-1β was measured in THP-1 derived macrophages after 24 h incubation with the chitosan particles with or without priming of the cells with LPS. We found that chitosan particles of both sizes stimulated upregulation of NFκB and IL-1β in the absence of LPS. Finally the dependence of this effect on inflammasome-mediated activation of caspase-1 was assessed. Active caspase-1 was not detected in THP-1- derived macrophages stimulated with chitosan-based viscoelastic hydrogel particles, neither alone nor in combination with LPS. In conclusion, we show that viscoelastic chitosan particles in the size range of 10-200 μm, are taken up by human APCs. Moreover, our study suggests that the chitosan particles stimulate NFκB upregulation and IL-1β secretion through inflammasome activation via a caspase-1 independent pathway.