Developmentally distinct CD4⁺ Treg lineages shape the CD8⁺ T cell response to acute Listeria infection

CD4⁺ regulatory T cells (Tregs) must prevent immunopathology by cytotoxic CD8⁺ T lymphocytes (CTLs) responding to acute infection and restore immune homeostasis following pathogen clearance, yet little is known about the specific populations or mechanisms governing these discrete events. We found that acute Listeria monocytogenes (L. monocytogenes) infection produces a phenotypically and functionally complex Treg response comprising two separate suppressor cell subpopulations, with an early Treg peak occurring at 24 h postinfection and a later peak arising by day 7. The first wave of Tregs suppress primary CTL expansion via a contact-independent mechanism involving CD73-derived adenosine (Ado) production from extracellular adenosine monophosphate (5′-AMP), while the second originates from different precursors and acts throughout the contraction phase via contact-dependent gap junction transfer of 3′,5′-cyclic adenosine monophosphate (cAMP)—both potent inhibitors of T cell proliferation. We speculate that the early activation of CD73 on Tregs is enhanced in inflamed tissues due to high purine release from apoptotic cells, whereas late-phase gap junction–dependent Tregs rely more on cell number and less on tissue inflammation. This study importantly reveals that CTL priming and contraction phases are separately fine-tuned by developmentally distinct Treg lineages during an acute infection.