The Small GTPase Rac2 Controls Phagosomal Alkalinization and Antigen Crosspresentation Selectively in CD8+ Dendritic Cells

Abstract

A unique subpopulation of spleen dendritic cells (DCs) that express the CD8 surface marker efficiently present phagocytosed antigens to CD8(+) T lymphocytes in a process called "crosspresentation," which initiates cytotoxic immune responses. We now show that the small GTPase Rac2 plays a critical role in antigen crosspresentation selectively in this DC subpopulation. In CD8(+) DCs, Rac2 determines the subcellular assembly of the NADPH oxidase complex (NOX2) to phagosomes, whereas in CD8(-) DCs, Rac1 mediates the assembly of NOX2 at the plasma membrane. In the absence of Rac2, the production of reactive oxygen species (ROS) in DC-phagosomes was abolished, the phagosomal pH dropped, and the efficiency of antigen crosspresentation was reduced. We conclude that the activity of Rac1 and 2 control crosspresentation in DC subpopulations through the regulation of phagosomal oxidation and pH.

CD81 Controls Immunity to Listeria Infection through Rac-Dependent Inhibition of Proinflammatory Mediator Release and Activation of Cytotoxic T Cells

“…Thus, Batf3 proteolytic activity in endosomes. This efficient cross-presentation relies on Rac, because in the absence of Rac, CD8a + cDCs behave like other phagocytes in terms of phagosomal acidification and crosspresentation (23,25). Contrasting observations that Rac activity is impaired in CD81 2/2 DCs (54), our data show that CD81 2/2 DCs exhibit persistent Rac activation, which could account for the high capacity of these cells to present bacterial Ags to specific CD8 + T cells during Listeria infection in vivo.…”

“…The recruitment of NOX2 to the phagosomes leads to the generation of ROS in CD8a + cDCs, which are also dependent on Rac2 (25). Our data revealing that CD81 inhibits Rac activation through direct association prompted us to investigate whether CD81 deficiency interferes with the production of ROS in DCs during Listeria infection.…”

“…Another splenic DC subset, namely CD8a + conventional DCs (cDCs), is responsible for the final resolution of infection against Listeria through the cross-priming of bacterial-derived Ags to specific CD8 + T cells and the subsequent induction of the cytotoxic T cell response (21,22). Interestingly, Ag cross-presentation in DCs requires endosomal alkalinization through reactive oxygen species (ROS) production resulting from NADPH oxidase (NOX) 2 recruitment, a process dependent on the small GTPase Rac (23)(24)(25). Additionally, a direct interaction between CD81 and Rac was revealed by proteomics analysis (26), suggesting that CD81 could modulate the cross-priming capacity of DCs.…”

RNAi screen for kinases and phosphatases that play a role in antigen presentation by dendritic cells

“…To identify genes involved in cross-presentation, we applied an shRNA-based genetic screening approach [4][5][6] Immunol. 2012Immunol.…”

Induction of respiratory immune responses in the chicken; implications for development of mucosal avian influenza virus vaccines

“…In chicken, it is not known which cell type is responsible for priming of naive T cells and whether a functional distinction between MPh and DC in priming capacity exists. In mouse, the endosomal compartment of DC has a near neutral pH (Savina et al 2006;Savina et al 2009), while MPh have much lower phagosomal pH (Yates and Russell 2005). In mouse, the decreased phagosomal acidification in DC reduces Ag proteolysis to a level that allows processing but does not fully destroy antigenic peptides.…”