Two-photon imaging of endogenous regulatory T cell dynamics and suppression of helper T cell priming mediated by CTLA-4 (IRC11P.441)

Despite the major role played by regulatory T cells (Tregs) in immune homeostasis, our knowledge on mechanisms involved is still incomplete. Using two-photon microscopy we characterize the behavior of endogenous Tregs under steady-state conditions, during inflammation, and during an antigen-specific T cell response in lymph nodes. Under steady-state conditions, endogenous Tregs maintain the highest average velocities of any cells in the lymph node and exist as two non-overlapping populations that explore the T-zone and the B cell follicle. In the T-zone, Tregs migrate more rapidly than conventional T cells (Tconv), extend longer processes, and interact with resident dendritic cells (DC) and Tconv. Under inflammatory conditions, Tregs engage migratory DCs near the lymph node capsule, occasionally form long-lived Treg-DC interactions. During antigen specific immune response, Tregs interact with antigen-induced DC:Tconv clusters, while continuing to form contacts with activated Tconv. We investigated the role of CD80/86-CTLA4 interactions during Tconv-Treg cell interactions. Blocking CTLA-4 reduces Treg-Tconv interaction times, increases the volume of DC:Tconv clusters, and enhances proliferation of antigen-specific Tconv in vivo . Furthermore, genetic deletion of CD80/CD86 on Tconv makes them less susceptible to inhibition by Tregs. Our results demonstrate a role for altered cellular choreography of Tregs through CTLA4-based interactions to limit helper T cell priming.