Pfaller, Christian

Abstract Introduction Bone marrow (BM) is the primary immune organ responsible for stem cell maintenance. Neurotropic infections elicit sequestration of T cells within the BM. Changes of the BM niche during brain viral infections are unknown. Intracranial infection with the neurotropic Theiler’s Murine Encephalomyelitis Virus (TMEV) in C57BL/6 mouse is cleared by 30 days due to generation of an antigen-specific CD8 T cell response. Methods We used brain viral infection and injury models to test T cell responses against brain antigens in the bone marrow. Results We determined that 1-10% of CD8 T cells present in the sternal, femoral, and cranial BM were virus antigen-specific 7 days post intracranial infection. Over 70% of these CD8 T cells were tissue resident. We determined antigen-specific CD8 T cells were generated in the BM within 4 days of infection. Continuous treatment with FTY720, which sequesters T cells outside of the blood, did not eliminate antigen-specific CD8 T cells in any BM compartment. CD8 T cells in the BM established durable memory populations and were reactivated upon antigen reencounter. In the memory phase (200 days post brain TMEV infection), bone marrow resident CD8 T cell could be reactivated upon cognate peptide delivery. Such reactivation of antigen specific memory CD8 T cells caused an increase in lineage-, Sca-1+, ckit + (LSK) cells in the BM in a CD8 dependent manner. Similarly, injection of the model antigen AF488-conjugated OVA mixed with Poly IC into the brain recapitulated antigen specific CD8 T cell generation within the bone marrow and further demonstrated the antigen presenting cell involved in the response to be a CD103 expressing myeloid DC. We conclude that viral infections and inflammatory stimulation in the brain induce in situ effector and memory T cell responses within the BM which is associated with significant stem cell dysregulation. Conclusion Our data paves the way for crucial studies of BM resident antigen-specific CD8 T cells in health and disease. Funding Source NIH K99/R00 Topic Categories Viral Immunology (VIR)

Abstract Introduction Peripheral nervous system innervation of various organs has been associated with the development and maintenance of the immune system. Yet, the intricate details of thymic innervation remain less well-studied. Interestingly, various neurological insults including brain tumors, and neurotropic infections have been shown to have profound impacts on thymic size and cellularity and T cell development. Methods We used flow cytometry, confocal microscopy, neuro tracers, and genetic knockout mice to evaluate developing T cell-neuron interactions within the thymus. Results We have identified neuronal cell bodies within the thymus. These cells express neuronal markers such as NeuN and tyrosine hydroxylase and lack TEC identifiers, such as EpCAM, UEA-1, and Ly51. Thymic neurons can be infected with a neurotropic rabies vector, further cementing their neuronal identity. Considering the thymus consists mostly of T cells, we next investigated a potential interaction between T cells and thymic neurons. Interestingly, loss of T cell development results in a lack of thymic neuron development indicating T cell-neuron coregulation during development. However, thymic neurons can be recovered following a bone marrow transplant, suggesting the provision of a differentiation and/or survival signal for neurons provided by the developing T cells. Using knockout mice lacking the T cell lineage at various stages of development, we determined that TCR beta selection is required for the development of thymic neurons. Finally, we determined that a lack of transition from DN4 to DP severely diminishes the development of thymic neurons. Analysis of the publicly available bulk RNA-sequencing data comparing thymic DP to DN cell populations indicates the potential involvement of IL34 in neuronal development in the thymus. Conclusion We describe a novel population of neuronal cells within the thymus that interact with developing thymocytes to establish optimal thymic architecture. Funding Source NIH K99/R00 Topic Categories Neuroimmunology (NEUR)