Microplastics amplify the pro-inflammatory response to fungal mycelial fragments and spores in neutrophil-like cells.

BACKGROUND: Microplastic pollution has emerged as a global environmental crisis with potential adverse consequences on human health. Mixtures of microplastics with fungal particles including mycelial fragments or spores are highly probable exposure scenarios occurring in various occupational settings or in moldy built indoor environments. However, immunotoxic outcomes associated with such exposure remain poorly characterized. Most studies have focused on single-exposure components. Here, we investigated, for the first time, the immunotoxic effects of microplastics mixed with spores or mycelial fragments from Aspergillus fumigatus on human neutrophil-like cells. MATERIALS AND METHODS: Differentiated HL60 neutrophil-like cells were exposed to 0-100 μg/mL HDPE microplastics mixed with 10(6) heat-inactivated mycelial fragments or spores for 24 h. RESULTS AND DISCUSSION: HDPE combined with fungal fragments induced significant release of IL-6 and IL-8 while the mixtures with fungal spores induced only IL-6 release from the neutrophil-like cells. Most importantly, we observed a trend of decreasing IL-6 levels with increasing doses of HDPE microplastics in mixture with fungal particles, indicating possible dysregulation of the pro-inflammatory response. The tested doses of HDPE microplastics in mixture with fungal particles showed no significant acute effects on the cell viability. Using HEK293-TLR reporter cells, we found no significant activation of TLR2 and TLR4 by HDPE microplastics, fungal particles, or their combination, suggesting that the release of IL-6 and IL-8 is induced through other innate immune-signaling pathways. Taken together, fungal particles as microbial contaminants, seem to be the main drivers of the immune responses triggered by exposure to mixed HDPE microplastics and fungal particles. Among these, fungal mycelial fragments appear to be the most potent compared to fungal spores that are typically monitored for risk assessments.