Study On The Mechanism Of SIV Infection Of Blood - Brain Barrier

AIDS, acquired immune deficiency syndrome, caused by the human immunedefici-ency virus (human immunodeficiency virus comes, HIV) infection. HIV enters and attacks the immune system, usually accompanied with a severe nerve system invasion. The common clinical symptoms were increasing of number of astrocytes and perivascular macrophages infiltration.The present study showed that HIV/SIV could enter into the central nervous system (CNS) through the blood brain barrier (BBB). There are several different hypotheses about the infection mechanism, which were accepted widely:(1) Virus directly enter the CNS; (2) Monocyte/Macrophage invasion; (3) Induced by T cells; (4) liquid mediated into the cell. On the whole, the virus (in the form of free virus or using infected cells as the carrier) can enter into the central nervous system through the close connection between endo-thelial cells or the endothelial cell. Therefore, the cerebral vascular endothelial cells which were the main component of blood-brain barrier was the first barrier of the virus into nervous system. So, in the process of infection, whether endothelial cells blocking the virus, is there a selective blocking? So we have three parts to research possible mechanism of the SIV through the blood brain barrier.PART 1:Isolate the SIV strains from different sources and analyze the sequence of gp120. We found that some rhesus monkey infected with SIV appeared typical AIDS with bowel disease symptoms, and some others appeared a significant central nervous pathological changes also known as the symptoms of AIDS encephalopathy. Whether these differences in clinical symptoms have relationship between the variation of virus sequence, especially in the combination region of virus and cells. Gp120 proteins play a key role in this process. Identification of the envelope protein Gp120 sequence of different tropism virus will promoting the study on the molecular mechanism of AIDS related bowel/brain disease.We isolated the virus from different infected rhesus monkeys with different symptoms:intestinal symptom or neural symptom and alignment the sequences of gp120. There are obvious different in gp120 sequence between the intestinal symptom and neural symptom. The diversity in amino acid sequence of intestinal symptom and neural symptom strains concentrated in the V1 and V4 area of Gp120. Intestinal symptom strains had an addition of glycosylation site in V4 but the glycosylation sites changes of neural symptom strains were located in conservative district, especially C1 area. The difference between the intestinal symptom and neural symptom strains did not locate in Gp120 V3 area which closely related with the tropism of strains.PART 2:Identification of infect-related receptors expressed on the endothelial cells (RF/6A). At the peak and the plateau of virus infection, there are a lot of free viruses in the peripheral blood, provides an opportunity and a long time for virus infection of endothelial cells. A lot of research found that HIV/SIV existed in the brain capillary endothelial cells. In vitro experiments have confirmed that the HIV virus can infect vascular endothelial cells and the variant SIV strains can also infect BMECs directly. However, BMECs have no CD4 molecules combined with Gp120. So in the absence of CD4 receptor, how dose the virus infect the endothelial cells?Our study found that endothelial cells (RF/6A) don’t express CD4 neither in the molecular level nor in protein level. Other infect-related receptor, such as CCR5, CXCR4, GPR15 (BOB), STR33 (BONZO), CCR2, CXCR7and CX3CR1 can be detected. So RF/6A cells does not fully express CD4 receptor, but a small amount of CCR5, CXCR4, CCR2, CX3CR, BOB and BONZO proteins. Most of receptors mediated the infection rely on CD4, but CCR5 and CXCR4 receptors can use CD4 independent ways. This should be the main way of virus infect the endothelial cells.PART 3:The comparation of infection of endothelial cells with different strains and different ways. Some researches have found that macrophage-tropism SIV strains can passage and choose a easy form of strains get into the monkey’s chamber through the blood, leading the occurrence of central nervous system diseases. We selected the different sources and different tropism of SIV and SHIV virus infects endothelial cells(RF/6A) directly. We found that the virus can infect endothelial cells, but at a lower level, only can be detected in molecular level and can’t detect the expression of viral proteins. And different sources and different tropism of the virus have no significant differences in infection of RF/6A. There is no choice of these strains in the process of infection of endothelial cells.New research also found that infected cells and normal cells can form a virological synapse structure and transfer a large number of virus. This way of infection have more about 100 times than the way of infection wirh free virus particles. The endothelial cells do not express CD4 molecules, but highly express a variety of glycoproteins and proteoglycans which have strong adhesive with lymphocytes and mononuclear macrophages. Wheather is it possible to transfer virus through the virological synapse structure? We infect RF/6A cells with CEMxl74 cells and found that this way can effectively promote the infection of RF/6A cells, raise the level of virus replication. But there are still no differences of infection between different source and different tropism Virus.Overall, we found that main way of SIV enter BBB should be the infection of endothelial cells with infected cells as a carrier. A large number of infected cells (mononuclear macrophages and T cells) transfer virus into endothelial cells in high efficient and let the virus get into the brain parenchyma. While free virus infection also existed, but due to its low efficiency of infection, is not the main way. The phenomenon of low infection may be associated with the lack of CD4 receptor. In the absence of CD4, other auxiliary receptor mediated efficiency is low. Additionly, the endothelial cells have no choice on different sources and different tropism virus. The reason of the monotonicity on sequence and tropism of brain seperated virus required further studies.