Micro- and nanoplastics reduce the phagocytosis and intracellular killing of E. coli by THP1-Blue™ NFκB monocytes.

Abstract

Purpose: Micro- and nanoplastic particles occur ubiquitously in the environment and have been detected in various organs in animals and humans. We studied, how micro- and nanoplastic influence phagocytosis and intracellular killing of live bacteria in human monocytes.

Methods: Cells of the human reporter cell line THP1-Blue™ NFκB were pre-treated with different concentrations of micro- and nanoplastic (diameter 1 μm and 100 nm) and then incubated with Escherichia coli DH5α. Phagocytosis and intracellular killing was studied using an antibiotic protection assay. The activation of the NFκB promoter was quantified by measuring the production of alkaline phosphatase. Cytokines were measured by enzyme immunoassay. Cell viability was determined by trypan blue staining and lactate dehydrogenase measurement. Electron microscopic images were taken to localize micro- and nanoplastic.

Results: Micro- and nanoplastic particles were rapidly internalized by monocytes. They reduced phagocytosis of E. coli in a concentration- and time-dependent manner. Exposure to micro- and nanoplastic also reduced the intracellular killing of bacteria in a concentration-dependent manner. Plain plastic particles did not induce NFκB synthesis and IL1β and IL6 release. At concentrations inhibiting phagocytosis, micro- and nanoplastic was not cytotoxic. Endotoxin stimulated phagocytosis of bacteria. High concentrations of plastic particles reduced the stimulatory effect of endotoxin on phagocytosis of bacteria, but not the effect on NFκB synthesis.

Conclusion: Exposure to micro- and nanoplastic reduced the ability of phagocytes to internalize and kill bacteria. High plastic concentrations decreased the endotoxin-stimulated phagocytosis of bacteria. Hence, exposure to plastic particles may reduce the host`s immune defence against bacterial pathogens.