Dynamic capping of CD25 occurs at point of contact prior to delivery of IL-2 from dendritic cell to Treg hybridoma. (50.12)

Abstract

Abstract CD4+CD25+ regulatory cells (Tregs) depend on external IL-2 for expansion, homeostasis and function, but the process of IL-2 delivery to Treg is poorly understood. We reported that IL-2 producing dendritic cells (DCs) control Treg function in vitro and that IL-2 delivery to Treg requires cell:cell contact and CD25. To further explore DC delivery of IL-2 we demonstrated that IL-2 producing dendritic cells similarly controlled suppressor function of CD4+CD25+ Treg hybridoma cells RD6, then studied the fate of DC-derived material and CD25 using live cell imaging and confocal microscopy of dye-labeled or IL-2mCherry transfected DCs and dye-labeled or CD25-AcGFP transfected RD6. Conjugate formation between DCs and RD6 was independent of IL-2 and CD25. However, the uptake of DC-derived material into RD6 cells required both IL-2 sufficient DCs and CD25. RD6 internalized DC-derived material from dye-labeled WT DCs and IL-2mCherry-expressing IL-2 KO DCs but not mCherry-expressing IL-2 KO DCs. Anti-CD25 blocked internalization of DC-derived material. RD6 exhibited dynamic capping of CD25 to the point of contact with IL-2 sufficient DCs, but showed no redistribution of CD25 after contact with IL-2 deficient DCs. CD25 capping preceded the release of IL-2 from the DC. The data indicate that IL-2 delivery from DC to RD6 involves membrane remodeling with spatial redistribution of CD25 to the DC contact site, raising the possibility for actin-cytoskeletol control of IL-2 delivery in Tregs.