Imaging of HIV-1 spread from T cells and Macrophages to Astrocytes

Thesis

CD4+ T cells and macrophages are the principal targets of HIV-1. They can be productively infected with the virus and transfer virions to contacting bystander cells. It has been suggested that soon after initial infection, free virions and virus-bearing or infected T cells and macrophages can enter the brain, triggering a cascade of inflammatory signals and recruitment of other immune cells. Chronic inflammation and increased viral antigens in the brain lead to HIV-1 associated neuropathy.

Once free virions or infected cells enter the central nervous system, the first type of brain cells that they are likely to encounter are astrocytes, which extend endfeet around the blood vessels. These cells have been observed to contain virions and viral products, but their permissivity to productive infection has not been clearly demonstrated. By contrast, productive infection of resident microglia and perivascular macrophages is well established.

Here, I investigate the permissivity of astrocytes to HIV-1 infection and found no evidence of infection by the free route. However, I found that astrocytes intimately contact HIV-1 infected macrophages and CD4+ T cells and, in some cases, extend filopodial membrane toward the infected cell. In astrocyte-T cell contact sites, termed synapses, virions appear to move along the astrocytic filopodia from the T cell to the astrocyte. In this case, the target cell mediated viral transfer across the intercellular gap.

HIV-1-infected macrophages released virus that associated with astrocytes, remaining either on the surface of the astrocytes or within intracellular compartments. HIV-1 bound to astrocytes could be transmitted efficiently to permissive cells in trans. However, astrocyte-associated virus was sensitive to inhibitors including proteases and neutralizing antibodies, suggesting a surface-accessible compartment. This work provides insight into mechanisms of HIV-1 spread in the brain from infected CD4+ T cells and macrophages to astrocytes and their potential as virus reservoirs.

I also optimized high resolution, correlative focused ion beam scanning electron microscopy technology to answer fundamental biological questions. I demonstrate the application of the technology to study skeletal muscle cell differentiation mechanisms. I combine the power of genetic mapping with structural analysis to qualitatively and quantitatively describe cellular states and functions. Using semi-automatic image processing analysis, I was able to compute high volumes of data and generate statistics that relate quantitative measurements of cellular structures to functions. The toolset developed here will be instrumental in studying cells and tissues in both research and clinical applications.

Authors: Do, TP

• Publication date: 2014
• DOI: 10.5287/ora-441dqgb6k
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: immunology; infectious diseases; HIV/AIDS; biology
• Subjects: HIV/AIDS; Biology; Immunology; Infectious diseases