EFFECTS OF TUMOR-NECROSIS-FACTOR-ALPHA AND INTERLEUKIN-6 ON FLUID-PHASE PERMEABILITY AND AMMONIA DIFFUSION IN CNS-DERIVED ENDOTHELIAL-CELLS

Background: Proinflammatory cytokines tumor necrosis factor-alpha (TNF -alpha) and interleukin-6 (IL-6) play an important role in the blood-b rain barrier breakdown present in several neurological diseases includ ing multiple sclerosis and AIDS. However, the specific effects of thes e cytokines on central nervous system-derived endothelial cells (CNS-E C) is not fully understood. In this study the effects of TNF-alpha and IL-6 were tested on different permeability mechanisms of CNS-EC. Meth ods: Central nervous system endothelial cells were isolated from human brain and retina and cultured in vitro in a transwell system. Fluid-p hase endocytosis and transcytosis, absorptive-mediated endocytosis, an d ammonia diffusion were measured with specific methods. Endothelial c ells were studied with electron microscopy for the ultrastructural eff ects of cytokine stimulation. Results: Fluid-phase endocytosis and tra nscytosis were significantly increased by TNF-alpha and IL-6. This eff ect was dose dependent and reversible. The ammonia diffusion rate was also significantly increased by TNF-alpha, Absorptive-mediated endocyt osis was not enhanced by TNF-alpha. Ultrastructural analysis of cytoki ne-treated CNS-EC confirmed the alterations in permeability showing an increase in endocytotic activity and a decrease in tight junctions. C onclusions: The proinflammatory cytokines IL-6 and TNF-alpha induce sp ecific changes in the morphology and permeability of CNS-EC. These alt erations can be important in many diseases characterized by increased cytokine production.