Immune profiling of human blood cells after indirect exposure to crystalline silica particles

Occupational exposure to respirable crystalline silica (RCS) is a significant health concern associated with pulmonary and systemic diseases, mediated in part through lung macrophage toxicity. In this study, we employed an ex vivo indirect exposure model, to explore potential links between silica-induced macrophage toxicity and changes in innate and adaptive immune cell phenotypes, that may contribute to systemic effects of RCS. THP-1 derived macrophages served as a macrophage model and were exposed to crystalline silica particles. Whole blood was subsequently exposed ex vivo to conditioned medium (CM) from these particle-exposed cells. We then characterized immune cell responses via soluble cytokine analysis and single cell profiling by mass cytometry. Two crystalline silica types were compared, Min-U-Sil 5 quartz (Minusil) and synthetic quartz (gQ), that differ in "nearly free silanols" (NFS)-functional groups linked to RCS pathogenicity. In one set of experiments, an immune stimulation cocktail was added during the last 4 h of exposure to observe potential Minusil-induced changes in cellular immune responses. The findings demonstrated that exposing whole blood to Minusil CM significantly elevated soluble pro-inflammatory cytokines levels. At the single cell level, Minusil CM exposure altered monocyte and dendritic cell subpopulation frequencies and increased frequencies of several lymphocyte populations with high expression of the early activation marker CD38. Following immune stimulation, two cytotoxic effector memory T cell subpopulations showed increased frequencies: one polyfunctional and one characterised by a high expression of CD161. This study provides novel data on immune cell profiles associated with ex vivo exposure to RCS.