Assessing the impact of airborne particulate pollution on human skin utilizing a novel human skin equivalent containing MUTZ-3-derived Langerhans cells

Air pollution is an exogenous stressor known to have a detrimental impact on skin health through the induction of inflammation; however, the direct effect of topical pollution exposure is still being elucidated. Human skin equivalents (HSE) aim to reproduce in vitro the structure and function of the native skin tissue. However, HSEs typically lack skin-resident immune cells, which could play a key role in the inflammatory response induced by pollution exposure. We outline the development of a HSE-containing MUTZ-3-derived Langerhans cells (MUTZ-3-LCs), which show dendritic morphology and Langerhans cell marker expression. We demonstrated that HSE-containing MUTZ-3-LC have lower basal levels of proinflammatory cytokines, but topical stimulation with allergens and irritant compounds induced a greater inflammatory response in these models compared to HSE without immune cells. To study the effect of pollution, we created a technique to apply diesel particulate matter (DPM) to HSEs. Though our microscopic analysis demonstrated that DPM does not penetrate the stratum corneum, we showed that DPM did induce production of proinflammatory cytokines, but notably only in HSEs containing MUTZ-3-LCs. These data suggest that topical exposure to air pollution can induce cutaneous inflammation and that skin-resident immune cells contribute to this response. This highlights the significance of immune-competent HSEs to the study of exogenous stressors in vitro.