Viral proteins and blood brain barrier

Impaired function of the brain vasculature and the breakdown of the blood-brain barrier might be critical factors in the mechanisms of HIV-1 virus trafŽcking in the central nervous system (CNS). Evidence indicates that the viral gene product, protein Tat, is partially responsible for these effects. In the present study, we tested the hypothesis that Tat can upregulate adhesion molecules and inammatory cytokines and, thereby facilitating entry of infected monocytes to the brain. C57BL/6 mice were injected with 25 mg Tat into the right hippocampus, and expression of inammatory mediators such as adhesion molecules (ICAM-1 and VCAM-1), chemokines (MCP-1) and inammatory cytokines (TNF-a) were determined by RT-PCR and immunocytochemistry. The most marked induction of VCAM-1, MCP-1 and TNF-a protein expressionwas observed at the site of Tat injection. However, induction of the ICAM-1, MCP-1 and TNF-a genes also was evident in discrete regions of the brain, such as hippocampus, frontal cortex, and corpus striatum. A series of double immunostaining studies was performed to determine the localization of inammatory mediator expression in the brain tissue. These experiments revealed strong inammatory responses from macrophages/microglia and astrocytes. Vascular brain endothelium also overexpressed inammatory mediators; however, this expression was less intense as compared to perivascular macrophages or glial cells. Our studies also revealed a strong inŽltration of vascular monocytes into the brain tissue in response to Tat injections. These data demonstrate that intracerebral administration of Tat can induce profound proinammatory effects, associated with monocyte inŽltration, in the brain tissue. These results are relevant to the mechanisms of the blood-brain barrier breakdown andHIV entry into the CNS. (Supported by grants from NINDS and NIMH). 88 The blood-brain barrier in the neuropathogenesis of HIV-1 infection H. Nottet, J. Middel, L. Boven, C. Pereira UMC Utrecht (Utrecht, NL)