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Immunity. 2009 Apr 17;30(4):544-55. doi: 10.1016/j.immuni.2009.01.013. Epub 2009 Mar 26.

The small GTPase Rac2 controls phagosomal alkalinization and antigen crosspresentation selectively in CD8(+) dendritic cells.

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Institut Curie, INSERM U653, Immunité et Cancer, 26 rue d'Ulm, 75248 Paris, Cedex 05, France.


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.

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