Uptake of Chitosan Based Viscoelastic Hydrogel Particles by AntigenPresenting Cells and Activation of Innate Immune Responses
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 mm and 200 mm, 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, NFkB and IL 1b 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 NFkB and IL 1b 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 mm, are taken up by human APCs. Moreover, our study suggests that the chitosan particles stimulate NFkB upregulation and IL 1b secretion through inflammasome activation via a caspase 1 independent pathway.