Meningothelial cells as part of the central nervous system host defence

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Meningothelial cells (MECs) are the cellular components of the meninges protecting the brain and as such provide important barrier function for the central nervous system building the interface between neuronal tissue and the cerebrospinal fluid (CSF). MECs were previously shown to be involved in the clearance of waste products from the CSF and in maintaining the optic nerve microenvironment. In addition, MECs are involved in immunological processes in the brain by secretion of pro-inflammatory cytokines in response to various pathologically relevant stress conditions. In this study, we analysed the uptake of latex beads as well as bacteria by human MECs using flow cytometric analyses. We found that MECs are highly active phagocytes able of ingesting large amounts of latex beads, as well as Gram-positive and Gram-negative bacteria. Phagocytic activity of MECs was sensitive to nocodazole and cytochalasin D treatment to a varying degree depending on particle composition. Interestingly, Gram-positive bacteria such as Staphylococcus aureus are more readily taken up compared with Gram-negative Escherichia coli. In addition, pre-treatment of MECs with lipopolysaccharide (LPS) or phorbol-12-myristate-13-acetate (PMA) enhanced S. aureus uptake, whereas PMA but not LPS was effective in enhancing E. coli uptake. Thus, MECs are highly active facultative phagocytes likely important for the maintenance of CSF homeostasis and host defence in the central nervous system especially against Gram-positive bacteria.