Imaging regulatory T cell dynamics and suppression of T cell priming mediated by CTLA4

Foxp3(+) regulatory T cells (Tregs) maintain immune homeostasis through mechanisms that remain incompletely defined. Here, by two-photon imaging, we examine the cellular dynamics of endogenous Tregs. Tregs are identified as two non-overlapping populations in the T-zone and follicular regions of the lymph node. 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. Tregs intercept immigrant DCs and interact with antigen-induced DC:Tconv clusters, while continuing to form contacts with activated Tconv. During antigen-specific responses, blocking CTLA4-B7 interactions reduces Treg-Tconv interaction times, increases the volume of DC:Tconv clusters, and enhances subsequent Tconv proliferation in vivo. Our results demonstrate a role for altered cellular choreography of Tregs through CTLA4-based interactions to limit T cell priming.