PhD Candidate University of Minnesota Saint Paul, Minnesota, United States
Disclosure(s):
Foster Powers: No financial relationships to disclose
Introduction/Rationale: New vaccines against tuberculosis are impeded by gaps in knowledge about the CD4 T cell response to Mycobacterium tuberculosis (Mtb). Although millions of CD4 T cells are recruited to the lungs, few are activated by antigen recognition to carry out protective effector functions. And while phagocytic cells harboring intracellular Mtb benefit from direct recognition by CD4 T cells, the mechanisms of protection mediated by this physical interaction are unknown. New technical approaches are needed to decipher which CD4 T cell effector functions depend on cellular contact and to define which Mtb antigen specificities enable direct recognition of infected antigen presentation cells (APCs) via TCR-peptide:MHC II binding.
Methods: Using gentle tissue digestion and flow sorting, we isolated CD4 T cell/APC multiplets from the lungs of mice infected with fluorescent Mtb. We used microscopy, chip cytometry, and sequencing analyses to enable comprehensive phenotyping and visualization of the immunological unit that drives protective immunity against Mtb. Further, we used mixed bone marrow chimeras to determine whether protection mediated by the crucial cytokine IFN-γ depends on direct recognition.
Results: CD4 T cell/APC multiplets in the lungs were induced by Mtb infection, peaked at week 4 post-infection, and partially depended on MHCII expression by monocyte derived cells. Sorted multiplets visualized with microscopy were spatially consistent with immunological conjugates. Within the CD4 T cell repertoire of a mouse, there was relative enrichment of key Mtb-reactive TCR clonotypes among CD4 T cells interacting with Mtb+ APCs. Among cellular conjugates from the lungs of Ifng-/- mixed bone marrow chimeric mice, those unable to produce IFN-γ at the immune synapse had higher percentages of intracellular Mtb and failed to upregulate IFN-responsive pathways.
Conclusion: Direct CD4 T cell recognition of Mtb-infected APCs forms protective synapses that enrich Mtb-specific TCRs and focus IFN-γ–mediated immunity.
