Interaction of Listeria monocytogenes with human brain microvascular endothelial cells: InlB-dependent invasion, long-term intracellular growth, and spread from macrophages to endothelial cells

Invasion of endothelial tissues may be crucial in a Listeria monocytogenes infection leading to meningitis and/or encephalitis. Internalization of L. monocytogenes into endothelial cells has been previously demonstrated by using human umbilical vein endothelial cells as a model system. However, during the crossing of the blood-brain barrier, L. monocytogenes most likely encounters brain microvascular endothelial cells which are strikingly different from macrovascular or umbilical vein endothelial cells. In the present study human brain microvascular endothelial cells (HBMEC) were used to study the interaction of L. monocytogenes with endothelial cells, which closely resemble native microvascular endothelial cells of the brain. We show that L. monocytogenes invades HBMEC in an InlB-dependent and wortmannin-insensitive manner. Once within the HBMEC, L. monocytogenes replicates efficiently over a period of at least 18 h, moves intracellularly by inducing actin tail formation, and spreads from cell to cell. Using a green fluorescent protein-expressing L. monocytogenes strain, we present direct evidence that HBMEC are highly resistant to damage by intracellularly growing L. monocytogenes. Infection of HBMEC with L. monocytogenes results in foci of heavily infected, but largely undamaged endothelial cells. Heterologous plaque assays with L. monocytogenes-infected P388D1 macrophages as vectors demonstrate efficient spreading of L. monocytogenes into HBMEC, fibroblasts, hepatocytes, and epithelial cells, and this phenomenon is independent of the inlC gene product.