Immunity
Volume 36, Issue 5, 25 May 2012, Pages 782-794
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Article
Adaptor Protein-3 in Dendritic Cells Facilitates Phagosomal Toll-like Receptor Signaling and Antigen Presentation to CD4+ T Cells

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Summary

Effective major histocompatibility complex-II (MHC-II) antigen presentation from phagocytosed particles requires phagosome-intrinsic Toll-like receptor (TLR) signaling, but the molecular mechanisms underlying TLR delivery to phagosomes and how signaling regulates antigen presentation are incompletely understood. We show a requirement in dendritic cells (DCs) for adaptor protein-3 (AP-3) in efficient TLR recruitment to phagosomes and MHC-II presentation of antigens internalized by phagocytosis but not receptor-mediated endocytosis. DCs from AP-3-deficient pearl mice elicited impaired CD4+ T cell activation and Th1 effector cell function to particulate antigen in vitro and to recombinant Listeria monocytogenes infection in vivo. Whereas phagolysosome maturation and peptide:MHC-II complex assembly proceeded normally in pearl DCs, peptide:MHC-II export to the cell surface was impeded. This correlated with reduced TLR4 recruitment and proinflammatory signaling from phagosomes by particulate TLR ligands. We propose that AP-3-dependent TLR delivery from endosomes to phagosomes and subsequent signaling mobilize peptide:MHC-II export from intracellular stores.

Highlights

► AP-3 is selectively required for optimal MHC-II presentation of phagocytosed antigen ► AP-3-deficient dendritic cells induce impaired CD4+ T cell inflammatory responses ► AP-3 regulates TLR4 delivery to phagosomes and subsequent inflammatory signaling ► AP-3 regulates phagosomal peptide:MHC-II complex delivery to the cell surface

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