Abstract
Exposure to respirable fractions of crystalline silica quartz dust particles is associated with silicosis, cancer and the development of autoimmune conditions. Early cellular interactions are not well understood, partly due to a lack of suitable technological methods. Improved techniques are needed to better quantify and study high-level respirable crystalline silica exposure in human populations. Techniques that can be applied to complex biological matrices are pivotal to understanding particle-cell interactions and the impact of particles within real, biologically complex environments. In this study, we investigated whether imaging flow cytometry could be used to assess the interactions between cells and crystalline silica when present within complex biological matrices. Using the respirable-size fine quartz crystalline silica dust Min-u-sil® 5, we first validated previous reports that, whilst associating with cells, crystalline silica particles can be detected solely through their differential light scattering profile using conventional flow cytometry. This same property reliably identified crystalline silica in association with primary monocytic cells in vitro using an imaging flow cytometry assay, where darkfield intensity measurements were able to detect crystalline silica concentrations as low as 2.5 μg/mL. Finally, we ultilised fresh whole blood as an exemplary complex biological matrix to test the technique. Even after the increased sample processing required to analyse cells within whole blood, imaging flow cytometry was capable of detecting and assessing silica-association to cells. As expected, in fresh whole blood exposed to crystalline silica, neutrophils and cells of the monocyte/macrophage lineage phagocytosed the particles. In addition to the use of this technique in in vitro exposure models, this method has the potential to be applied directly to ex vivo diagnostic studies and research models, where the identification of crystalline silica association with cells in complex biological matrices such as bronchial lavage fluids, alongside additional functional and phenotypic cellular readouts, is required.
Highlights
Quartz is a common form of crystalline silica and is a major component of rocks, sands, and soils [1]
Conventional flow cytometry was used to determine whether the crystalline silica particle-induced shifts of side scatter (SSC) light profile were associated with particle dose
peripheral blood mononuclear cells (PBMC) is a mixed population of immune cells, consisting of lymphocytes, monocytes, natural killer cells and dendritic cells derived from peripheral blood
Summary
Quartz is a common form of crystalline silica and is a major component of rocks, sands, and soils [1]. Advances in the fields of microscopy and imaging flow cytometry have made it possible to generate fully quantitative imaging analyses that can detail the interactions and effects of micron and nano-sized particles in vitro and ex-vivo on primary cell populations [16,17,18,19,20,21]. Such techniques may assist in understanding the immunologic events which lead to autoimmune states initiated by exposure to respiratory fractions of crystalline silica
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