Abstract TP277: CD4 T Cells Increase Tyrosine Hydroxylase Expression With Aging and Stroke in Mice

Abstract

Introduction: Activated T lymphocytes are present in the brain and play a detrimental role in aging and potentiate inflammation after ischemic injury. Previous studies have shown that T lymphocytes (T cells) synthesize and secrete catecholamines that modulate their activation. Tyrosine hydroxylase (TH), is a rate-limiting enzyme in catecholamine synthesis. Little is known about the role and contribution of TH synthesis specifically in T lymphocytes in aging and ischemic stroke injury. We hypothesized that aging will lead to increase TH + T cells in the brain that will have an activated phenotype and contribute to the progression of ischemic injury. Methods: Young (8-12 weeks) and old (22-24 months) C57BL/6 male mice were used. Spleen, bone marrow and brain were harvested and flow cytometry was used to immunophenotype the TH + T cells. Expression of TH on sorted CD4 + and CD8 + T cells was assessed by a real-time polymerase chain reaction. Splenic lymphocytes were stimulated with PMA/ionomycin and different T cell subsets were analyzed. The CD4 + T cells were purified from young and old mouse spleens and ex vivo stimulated to measure cytokine production. Finally, young and old mice underwent 60 minutes of middle cerebral artery occlusion (MCAo) and were euthanized 4 days later to determine the role of TH + T lymphocytes in stroke injury. Results: The percentage and MFI of TH was increased on CD4 + T cells with aging however, no change in TH percentage or MFI on CD8 + T cells was observed. TH RNA was increased in CD4 + T cells derived from old animals. The TH + CD4 + T cells were activated and had an effector memory phenotype in aging. On acute stimulation, old TH + CD4 + T cells increased the production of INF-γ, IL-4, and Il-17. After MCAo the percentage TH + CD4 + T cells increased in both young and old mice in the brain. The MFI IL-4/INF-γ ratio was higher in the young MCAo versus old MCAo reflecting a Th2 related response. Conclusion: TH + CD4 + T cells increase with age. These cells have an activated and effector memory phenotype and secrete inflammatory cytokines on acute stimulation. After MCAo, TH + CD4 + T cells demonstrated Th2 related protective responses in only in young mice.