MHC class II compartments and the kinetics of antigen presentation in activated mouse spleen dendritic cells.
MHC class II (MHC-II) molecules bind fragments of exogenous Ags in an intracellular endocytotic compartment. In view of divergent data on the MHC-II distribution in different cell lines, it was of interest to localize MHC-II molecules in a natural and the most potent APC type, the dendritic cell (DC). By using immunogold labeling of ultrathin cryosections of cultured mouse spleen DC, we found that MHC-II molecules were present abundantly at the plasma membrane and in intracellular compartments containing internal membrane vesicles and/or membrane sheets. The majority of these compartments was situated late in the endocytotic route, as demonstrated by the late appearance (after a lag of 30 min) of internalized exogenous tracer. These compartments contained the lysosomal enzymes cathepsin D and beta-hexosaminidase, but lacked the late endosomal marker cation-dependent mannose-6-phosphate receptor. We conclude that most of the intracellular MHC-II molecules in cultured spleen DC reside in a compartment with (pre)lysosomal characteristics, resembling the so-called MHC-II-enriched compartments (MIIC), originally described in B cells. We also investigated whether the presence of MHC-II molecules in endocytotic compartments was related to the kinetics of Ag processing and presentation by these cells. Pulse-chase endocytosis experiments with hen egg lysozyme (HEL) as a model Ag showed that activated spleen DC were able to efficiently process and present this Ag to an HEL-specific T hybridoma cell line. However, presentation started only after a lag of 2 h and was maximal after 6 h. The difference in time between the arrival of Ag in proteolytic endocytotic compartments, in particular MIIC, and effective Ag presentation is discussed in the context of DC maturation.
Kleijmeer
M J
MJ
Department of Cell Biology, School of Medicine, Utrecht University, The Netherlands.
Ossevoort
M A
MA
van Veen
C J
CJ
van Hellemond
J J
JJ
Neefjes
J J
JJ
Kast
W M
WM
Melief
C J
CJ
Geuze
H J
HJ
D000818:Animals; D017951:Antigen Presentation / Q000276:immunology*; D002460:Cell Line; D003713:Dendritic Cells / Q000276:immunology* / Q000648:ultrastructure*; D004527:Egg Proteins / Q000276:immunology; D000949:Histocompatibility Antigens Class II / Q000276:immunology*; D051379:Mice; D008806:Mice, Inbred AKR; D016253:Microscopy, Immunoelectron; D009113:Muramidase / Q000276:immunology; D012710:Serum Albumin, Bovine / Q000276:immunology; D013154:Spleen / Q000166:cytology; D013601:T-Lymphocytes / Q000276:immunology
D004527:Egg Proteins; D000949:Histocompatibility Antigens Class II; D012710:Serum Albumin, Bovine; D009113:Muramidase