Constitutive macropinocytosis allows TAP-dependent major histocompatibility complex class I presentation of exogenous soluble antigen by bone marrow-derived dendritic cells.
Dendritic cells expanded from mouse bone marrow (BMDC) with granulocyte/macrophage-colony-stimulating factor have potent T cell-stimulatory properties both in vitro and in vivo. This has been well documented for major histocompatibility complex (MHC) class II-restricted responses, and more recently using peptide-loaded and protein-pulsed DC for CD8 responses following adoptive transfer in mice. An unresolved question concerns the capacity of BMDC to present exogenous antigen on MHC class I molecules, an unconventional mode of MHC class I loading for which there is now considerable evidence, particularly in macrophages. Here, we show that BMDC exhibit high levels of macropinocytosis driven by constitutive membrane ruffling activity. Up to one-third of actively ruffling and macropinocytosing BMDC transferred pinocytosed horseradish peroxidase into the cytosol following a 15-min pulse, suggesting that they might be capable of presenting exogenous soluble antigen on MHC class I molecules. We show that BMDC presented exogenous ovalbumin to a T cell hybridoma more effectively, more rapidly, and at lower exogenous antigen concentrations than BM macrophages on a cell-for-cell basis. Presentation was TAP dependent, brefeldin A sensitive, and blocked by inhibitors of proteasomal processing, demonstrating use of the classical MHC class I pathway. Although effective presentation of exogenous antigen by BMDC occurred in the absence of agents which stimulate macropinocytosis, treatment with phorbol myristate acetate (PMA) enhanced both pinocytosis and MHC class I presentation by BMDC. Finally, PMA-stimulated BMDC exposed to exogenous ovalbumin in vitro were able to prime an antigen-specific cytotoxic T lymphocyte response following adoptive transfer in vivo.
Norbury
C C
CC
Department of Biochemistry, Medical Sciences Institute, University of Dundee, Scotland.
Chambers
B J
BJ
Prescott
A R
AR
Ljunggren
H G
HG
Watts
C
C
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters / Q000502:physiology*; D000818:Animals; D000938:Antigen-Presenting Cells / Q000276:immunology*; D000941:Antigens / Q000737:chemistry / Q000276:immunology*; D001853:Bone Marrow / Q000276:immunology*; D001854:Bone Marrow Cells; D003713:Dendritic Cells / Q000276:immunology*; D015395:Histocompatibility Antigens Class I / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010873:Pinocytosis; D012995:Solubility
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters; D000941:Antigens; D015395:Histocompatibility Antigens Class I; C073119:TAP1 protein, human; C486171:Tap1 protein, mouse