Dendritic Cell-Induced Dissemination of Mycobacterium tuberculosis into the Central Nervous System

Abstract Central nervous system tuberculosis (CNSTB) is the most serious manifestation of extrapulmonary tuberculosis infections representing 5–10% of all cases. Knowledge of CNSTB stems from observations made in 1933 by pathologists Rich and McCordock, who found caseating foci in the brain parenchyma or meninges that rupture into the subarachnoid space leading to diffuse meningeal infection. However, the mechanism of how immobile Mycobacterium tuberculosis, the causative agent of TB crosses the highly regulated blood-brain barrier (BBB) and enters the CNS forming these foci and infection is unknown. We have developed a novel in vitro BBB model that combines Mycobacteria-infected DCs, PBMCs, and primary mouse brain endothelial cells to observe early cellular interaction and aggregate formation at the BBB similar to previous observations by Rich and McCordock. With this model we observed Mycobacteria impedes migration of DCs but increases DC initiation of aggregation on a primary mouse endothelial BBB with a cellular composition similar to pulmonary granulomas. Aggregates induce an inflammatory response by increasing ICAM-1 and VCAM-1 expression and dysregulation of tight junction proteins and mitochondria suggesting barrier damage possibly due to increased iNOS expression observed during within aggregates. Mycobacteria-infected DC transmigration is increased in the presence of aggregation. Previous research from our lab and others have shown DC transmigration across an in vitro BBB rely on MMP-9 secretion while TNF-alpha is necessary for pulmonary granuloma formation and Mtb infection control. Here we will show the role iNOS, MMP-9 and TNF-alpha play in DC-mediated dissemination of Mycobacterium across the BBB.