Group 1 Metabotropic Glutamate Receptor’s Influence on T Cells During Chronic Toxoplasma Infection

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PROJECT SUMMARY/ABSTRACT Toxoplasma gondii (T. gondii) is one of the most effective transmissible pathogens in the world, infecting approximately two billion people. Encystment of the parasite in neurons in the brain results in a lifelong chronic infection. Within the brain, a pro-inflammatory response is essential to prevent parasite reactivation. Infection in the immunocompromised leads to lethal toxoplasmic encephalitis while in the immunocompetent, there is persistent low-grade inflammation which lacks clinical symptoms. This suggests that there is a tightly regulated inflammatory response to T. gondii in the brain. T cells are the dominant immune cell that control recrudescence and parasite replication through secretion of effector molecules such as perforins and IFN-γ. However, little is known on how these cells are regulated in this tissue. During chronic infection there is an increase in extracellular (EC) glutamate. High EC glutamate is not specific to T. gondii infection and can occur during multiple pathologies but may be an important environmental signal to tissue specific immune cells. We hypothesize that this glutamate-rich environment plays a role in T cell function and regulation. Preliminarily data demonstrate that T cells from the T. gondii -infected brain express the G-protein coupled metabotropic glutamate receptors (mGluR’s), mGluR1 and mGluR5. This expression is enriched in T cells recruited to the brain compared to secondary lymphoid derived cells. This project aims to: 1) define group 1 mGluR expressing T cells in the brain during infection, and determine if there is a functional difference compared to the periphery. This will be done by characterizing surface proteins for canonical T cell subsets, testing the secretion of effector molecules, defining if they localize to distinct regions of the brain, and characterizing the transcriptional profile at a single cell level; 2) determine how group 1 mGluR’s regulate T cells in response to infection. This will be done by tracking adoptively transferred mGluR-deficient T cells in an infected wild type recipient, and by activating or inhibiting these receptors ex vivo, followed by measuring changes in viability, proliferation, cytokine production, and canonical Gq molecules; 3) determine if lowering the glutamate concentrations in the infected brain will alter the T cell recruitment profile to the central nervous system (CNS). This will be done by characterizing mGluR expressing T cells recruited to the brain after ceftriaxone treatment, an antibiotic previously used in our lab to lower exogenous glutamate in the brain by increasing glutamate transporter-1 expression. Overall, this proposal will help us understand how tissue- derived signals influence protective immunity. Furthermore, what we learn from our proposed studies could be broaden to other fields such as neurodegenerative research, as some of these neurological maladies not only have a commonality of glutamate alteration, but also a recruitment of T cells to the CNS.