title: The extracellular domains of MHC class II molecules determine their processing requirements for antigen presentation.
abstract: We have evaluated the relative contributions of the extracellular and cytoplasmic domains of MHC class II molecules in determining the Ag-processing requirements for class II-restricted Ag presentation to T cells. Hybrid genes were constructed to encode a heterodimeric I-Ak molecule in which the extracellular portion of the molecule resembled wild type I-Ak but where the connecting stalk, transmembrane and cytoplasmic domains of both the alpha- and beta-chain were derived from the class I molecule H-2Dd. Mutant I-Ak molecules were expressed as heterodimeric membrane glycoproteins reactive with mAb specific for wild type I-Ak. Fibroblast and B lymphoma cells expressing either wild type or mutant I-Ak molecules were able to process and present hen egg lysozyme (HEL) and conalbumin to Ag-specific, I-Ak-restricted, T cell hybridomas or clones. The mutant-expressing cells presented native and peptide Ag less efficiently than the wild type-expressing cells, suggesting that the disparity in presentation efficiency was not due to a difference in Ag processing. CD4 interaction was intact on the mutant I-Ak molecules. Presentation of native Ag by mutant and wild type-I-Ak-expressing cells was abolished by preincubation with chloroquine, or after paraformaldehyde fixation. After transfection of a cDNA encoding the gene for HEL, neither mutant nor wild type-I-Ak-expressing cells presented endogenously synthesized HEL to a specific T hybrid. Newly synthesized mutant I-Ak molecules were associated with invariant chain. These data demonstrate the ability of hybrid class II molecules to associate intracellularly with invariant chain and degraded foreign Ag in a conventional class II-restricted processing pathway indicating that the extracellular domains of class II molecules play a dominant role in controlling these Ag-processing requirements.
authors.affiliation: Department of Pathology and Immunology, Monash Medical School, Melbourne, Australia.
authors.forename: L
authors.initials: L
authors.lastname: Kjer-Nielsen
authors.forename: J D
authors.initials: JD
authors.lastname: Perera
authors.forename: L F
authors.initials: LF
authors.lastname: Boyd
authors.forename: D H
authors.initials: DH
authors.lastname: Margulies
authors.forename: J
authors.initials: J
authors.lastname: McCluskey
mesh_terms: D000818:Animals; D000938:Antigen-Presenting Cells / Q000276:immunology*; D015152:Blotting, Northern; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D015180:Electrophoresis, Gel, Two-Dimensional; D005110:Extracellular Space / Q000276:immunology; D015870:Gene Expression; D006183:H-2 Antigens / Q000235:genetics / Q000276:immunology; D000949:Histocompatibility Antigens Class II / Q000235:genetics / Q000276:immunology*; D008562:Membrane Glycoproteins / Q000276:immunology / Q000648:ultrastructure; D051379:Mice; D009113:Muramidase / Q000276:immunology; D012333:RNA, Messenger / Q000235:genetics; D011948:Receptors, Antigen, T-Cell / Q000276:immunology; D011994:Recombinant Proteins / Q000276:immunology; D013329:Structure-Activity Relationship; D014162:Transfection
chemical_list: D006183:H-2 Antigens; D000949:Histocompatibility Antigens Class II; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D011948:Receptors, Antigen, T-Cell; D011994:Recombinant Proteins; D009113:Muramidase