91 Transcriptomic profiling reveals immunomodulatory effects of welding particles in lung epithelial and macrophage-like cells

Abstract Welding fumes contain respirable particles rich in metals (eg iron, manganese, chromium, nickel) and are classified as Group 1 carcinogens by IARC. Despite epidemiological evidence linking welding fume exposure to increased lung cancer risk, underlying molecular mechanisms remain poorly understood. This study investigates acute toxicity and transcriptomic responses to welding particles from mild steel (MS) and stainless steel (SS) generated via gas-metal arc welding in human bronchial epithelial cells (BEAS-2B) and macrophage-like cells (THP-1). Cellular uptake was confirmed by TEM and quantified by ICP-MS, revealing similar metal content for the two cell types. Dose- and time-dependent reductions in metabolic activity were identified, particularly for SS. Bulk RNAseq revealed more differentially expressed genes (DEGs) in THP-1 compared to BEAS-2B cells and more DEGs for SS compared to MS. Pathways related to immune response were strongly enriched and activated in THP-1 cells for both particles and moderately activated or inhibited in BEAS-2B cells. Validation experiments confirmed increased cytokine secretion and DNA damage in THP-1 cells with stronger effects for SS. Both particles reduced cytokine secretion in BEAS-2B cells indicating an immunomodulatory response. To understand the role of cell-cell interactions in mediating the response we performed single-cell RNAseq after exposure to BEAS-2B and THP-1 in co-culture. BEAS-2B cells acquired a pro-inflammatory phenotype (eg increased CXCL8 in response to SS) when co-cultured with THP-1 cells compared to monoculture. Overall, our data highlights distinct cellular responses to welding particles and underscores the importance of particle composition, cell type and cell-cell interactions in mediating toxicity.