1. Department of Cell Biology and Section of Immunobiology, Ludwig Institute for Cancer Research, Yale University School of Medicine, 333 Cedar Street, PO Box 208002, New Haven, Connecticut 06520-8002, USA

Correspondence to: Ira Mellman¹ Correspondence and requests for materials should be addressed to I.M. (Email: ira.mellman@yale.edu).

Abstract

Dendritic cells have a unique function in the immune response owing to their ability to stimulate immunologically naive T lymphocytes¹. In response to microbial and inflammatory stimuli, dendritic cells enhance their capacity for antigen presentation by a process of terminal differentiation, termed maturation^{2, 3}. The conversion of immature to mature dendritic cells is accompanied by a marked cellular reorganization, including the redistribution of major histocompatibility complex class II molecules (MHC II) from late endosomal and lysosomal compartments to the plasma membrane^{4, 5, 6, 7} and the downregulation of some forms of endocytosis, which has been thought to slow the clearance of MHC II from the surface^{8, 9, 10, 11}. The relative extent to which these or other mechanisms contribute to the regulation of surface MHC II remains unclear, however. Here we find that the MHC II -chain cytoplasmic tail is ubiquitinated in mouse immature dendritic cells. Although only partly required for the sequestration of MHC II in multivesicular bodies, this modification is essential for endocytosis. Notably, ubiquitination of MHC II ceased upon maturation, resulting in the accumulation of MHC II at the cell surface. Dendritic cells thus exhibit a unique ability to regulate MHC II surface expression by selectively controlling MHC II ubiquitination.

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