Studies On The Mechanisms Underlying Pathogenesis Of HIV-1 In CNS And Neuroprotection Of Regulatory T Cells

The pathogenesis of HIV-1-associated neurocognitive disorders (HAND), the most common complication of HIV disease in CNS, is still unclear. Therefore, this study was designed to explore the underlying mechanisms. The Part One of this thesis is devoted to the contributions of inactivated HIV-1 particle to microglial activation, which aims to providing scientific basis for therapeutic drug discovery. The Part Two of this thesis is focus on the mechanisms of Treg induced neuroprotection, which sets stage for immune intervention of HAND.As we known, the entry of HIV-1 to target cells is mediated by its receptor (CD4) and co-receptors (CCR5 and CXCR4). Therefore, in the CNS, only microglia and perivascular macrophage express those molecules and are infected by HIV-1. Previous studies demonstrated that the neuroinflammation triggered by activated microglia/macrophage plays a key role in the initiation and development of HAND. In order to decipher the effects of HIV-1 particle on microglia, it is very important to obtain highly purified human microglia, which is described in the First Chapter of Part One. HIV-1 glycoprotein, gp120, amongst the most studied viral proteins in the pathogenesis of HIV disease, is shown to mediate the virus entry and involve in neuroinflammation. In the Second Chapter of Part One, we found that gp120 could activate microglia via triggering calcium influx, inducing ERK phosphorylation and stimulating NF-кB translocation in human microglia. Moreover, HIV-1 particle is considered as a supermolecule, because its surface incorporates both virus and host derived proteins. The comparison study showed that inactivated HIV-1 particles trigger much stronger calcium influx than gp120, so the host derived proteins must play an important role in microglial activation. Taken together, the drugs, which could block the microglial calcium influx triggered by either gp120 or HIV-1 particles, may incite neuroprotection.Recent research has demonstrated a neuroprotective role for Treg in a mouse model of HIVE. However, the mechanism is only partially understood, which are believed to resolve neuroinflammation elicited by HIV-1 infected microglia/macrophage. In Part Two of this thesis, we cocultured HIV-1/VSV infected macrophage with Treg to find how Treg modulate macrophage function. We demonstrated that Treg promote neuroprotection by inhibiting virion release, killing infected macrophages and inducing phenotypic switch. Surprisingly, Treg inhibits progeny virion release through upregulating ISG15, an ubiquitin-like protein involving in interferon-mediated antiviral immunity. Importantly, Treg kills infected macrophages through both caspase-3 and granzyme/perforin pathways. Independently, Treg transforms infected macrophages from M1 to M2 phenotype as demonstrated by downregulated inducible nitric oxide synthase and unregulated arginase 1 expression. Taken together, Treg affacts infected macrophage function and achieves neuroinflammation resolution during the course of HIV disease. These findings challenge the dogma of a solitary Treg immune suppressor function and provide novel insights into how adaptive immunosurviellance limits the severity of HAND.