BCG-Infected Dendritic Cells Induce TNF-alpha Dependent Cell Cluster Formation that Damage Brain Endothelial Cells in an In Vitro Model of the Blood Brain Barrier

Abstract Central nervous system tuberculosis (CNSTB) is the most serious manifestation of extrapulmonary tuberculosis infections representing 5–10% of all cases. How Mycobacterium tuberculosis (Mtb) crosses the highly regulated blood-brain barrier (BBB) and enters the CNS, is still not well understood. We showed previously that mycobacterium infected dendritic cells adhere to brain microvessel endothelial cells. Here, we applied a novel model of in vitro BBB consisting of primary brain astrocytes and microvessel endothelial cells to test the mechanisms of how mycobacterium infected dendritic cells (DCs) interact with peripheral blood mononuclear cells (PBMC) and affect the BBB. We show that infected DC migration was hindered but infected DCs induce cellular cluster formations containing PMBC and T cells in addition to DCs. These clusters contained 24% CD11c+, 57%CD11b+, and 16% CD4+ cells, while B220+ B cell number was negligible mimicking the cellular composition of pulmonary granulomatous-like lesions. PBMC and infected DC clusters strongly adhered to the in vitro BBB and induced cluster associated damage (CAD). CAD correlated with mitochondrial disorganization and the degradation of ZO-1, claudin-5 tight junction associated proteins, upregulation of cellular adhesion molecules VCAM-1 and ICAM-1 in endothelial cells. Anti-TNF-a inhibition reduced cluster formation as well as ICAM-1 expression on brain microvessel endothelial cells and mitigated CAD. This research will lead to better knowledge in understanding how mycobacteria affects the BBB that could lead to better therapeutic treatments for CNSTB infection.