Internalization of iscom-borne antigens and presentation under MHC class I or class II restriction.
Exogenous nonreplicating antigens (Ag) incorporated into immunostimulating complexes (iscoms) induce CTL responses under MHC class I restriction. A requirement for inducing CTL responses is that the Ag is delivered to the cytosol of antigen-presenting cells (APC), a route restricted to endogenously produced Ag. To investigate the mechanisms by which iscoms elicit MHC class I-restricted responses, the intracellular distribution of influenza virus envelope proteins incorporated in iscoms (flu-iscoms) or in micelles (flumicelles) was studied in vitro using murine peritoneal cells (PEC). Ultrathin sections of cells pulsed with biotinylated flu-iscoms or flu-micelles were analyzed by electron microscopy after detection of the biotin label by reaction with streptavidin-gold. PEC pulsed with flu-iscoms showed a pattern of scattered gold particles distributed in clear and dense vesicles as well as in the intracellular space but not associated with organelles. In cells pulsed with flu-micelles, Ag was also detected in most cellular compartments but at a considerably lower concentration. The intracellular distribution of particulate Ag in iscom or micelle form was confirmed by lysis and differential centrifugation of Ag-pulsed APC. Furthermore, P815 cells pulsed with flu-iscoms were lysed by specific immune effectors showing that the iscom-Ag was processed and presented by class I-expressing APC. Flu-iscoms were internalized about 50-fold more efficiently than ovalbumin iscoms (ovaiscoms) suggesting that the nature of the protein and/or the presence of cellular receptors are important factors influencing the capacity of APC to take up iscom-borne proteins. PEC accounted for the most active internalization of iscom-borne Ag, although splenic dendritic cells and B cells also took up fluiscoms with remarkable efficiency.
Villacres
M C
MC
Department of Veterinary Microbiology, Swedish University of Agricultural Sciences, Uppsala. villacre@hsc.usc.edu
Behboudi
S
S
Nikkila
T
T
Lovgren-Bengtsson
K
K
Morein
B
B
D000818:Animals; D017951:Antigen Presentation; D000938:Antigen-Presenting Cells / Q000276:immunology / Q000378:metabolism; D000956:Antigens, Viral / Q000378:metabolism*; D016175:B-Lymphocyte Subsets / Q000276:immunology / Q000378:metabolism; D019921:Biotinylation; D002458:Cell Fractionation; D002460:Cell Line; D002499:Centrifugation, Density Gradient; D003713:Dendritic Cells / Q000276:immunology / Q000378:metabolism; D005260:Female; D006183:H-2 Antigens / Q000502:physiology*; D000949:Histocompatibility Antigens Class II / Q000502:physiology*; D016882:ISCOMs / Q000276:immunology* / Q000378:metabolism; D007252:Influenza Vaccines / Q000276:immunology* / Q000378:metabolism; D007399:Interphase / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D008823:Micelles; D010047:Ovalbumin / Q000276:immunology; D010529:Peritoneal Cavity / Q000166:cytology
D000956:Antigens, Viral; D006183:H-2 Antigens; D000949:Histocompatibility Antigens Class II; D016882:ISCOMs; D007252:Influenza Vaccines; D008823:Micelles; D010047:Ovalbumin