Microglial immunity in Toxoplasmic encephalitis

Toxoplasma gondii is a foodborne parasite that infects one-third of humans worldwide and is an AIDS-defining pathogen. Parasite reactivation in the brains of HIV-infected individuals is a hallmark of progression to AIDS and can result in life-threatening Toxoplasmic encephalitis. T. gondii is among the most common opportunistic parasitic infections in AIDS patients and is the leading cause of focal CNS infection complicating AIDS. It is well established that peripheral immune cells, including T cells and monocytes, infiltrate the brain and are critical in immune defense during acute and chronic T. gondii infection. In contrast, the functions of brain- resident cells, such as microglia, during T. gondii infection are less well understood. Microglia actively survey the brain, respond to infection or injury, and phagocytose cellular debris. These cells are also infected by HIV and by T. gondii. Despite the sentinel role of microglia during infection and injury, there is less known about their functions during T. gondii infection, particularly during immune deficiency due to HIV/AIDS. The goal of this proposal is to determine the role of microglia in immune defense during T. gondii infection in the context of AIDS-associated immune deficiency. Our preliminary data indicate that microglia are a major source of the chemokine CCL2 during T. gondii infection, and that microglia increase antimicrobial pathways in response to T. gondii infection in the brain. The central hypothesis is that microglia contribute to protective immunity by recruiting peripheral immune cells to the brain, and by increasing antimicrobial mechanisms to control invading parasites. Two specific aims are proposed. In the first aim, the role of microglia-derived CCL2 in immune control will be examined during acute and chronic T. gondii infection, and in the context of T cell or IFN-g depletion to model HIV/AIDS immune deficiency. In the second aim, microglia activation in response to T. gondii will be visualized and quantified in real-time using intravital imaging of transgenic mice expressing a novel microglia-specific calcium reporter. We will also define the microglial transcriptional landscape during infection by conducting single-cell level gene expression analysis of T. gondii-infected brains using spatial transcriptomics. These experiments are expected to reveal how microglia respond to each stage T. gondii infection in the CNS. This research is significant because microglia are activated in response to a large number of inflammatory and infectious agents and may contribute to immune control in HIV/AIDS patients in the context of impaired T cell immunity. An understanding of how microglia recruit immune cells to the brain and exert antimicrobial functions may inform strategies to enhance microglial activities during CNS infection of AIDS patients with peripheral immune deficiency. The successful completion of the proposed research is also expected to contribute to an enhanced understanding of the role of microglia in the immune response in the context of chronic and reactivated CNS infection with the AIDS-defining pathogen T. gondii. Project Number: 1R21AI189465-01A1 | Fiscal Year: 2025 | NIH Institute/Center: National Institute of Allergy and Infectious Diseases (NIAID) | Principal Investigator: Melissa Lodoen | Institution: UNIVERSITY OF CALIFORNIA-IRVINE, IRVINE, CA | Award Amount: $227,018 | Activity Code: R21 | Study Section: HIV Coinfections and HIV Associated Cancers Study Section[HCAC] View on NIH RePORTER: https://reporter.nih.gov/project-details/1R21AI18946501A1