Human major histocompatibility complex class II invariant chain is expressed on the cell surface.
Class II major histocompatibility complex antigens are intracellularly associated with a nonpolymorphic polypeptide referred to as the invariant chain. Before the class II heterodimer appears on the cell surface, the invariant chain dissociates but it has so far been unclear as to whether or not a proportion of the invariant chain also appears on the plasma membrane. We describe a study with three monoclonal antibodies which recognize an extracytoplasmic determinant present on all forms of the invariant chain and use them to demonstrate its presence on the surface of the intact cells. The determinants recognized by two of the antibodies were found to be located within the 60 amino acids at the extreme C-terminal (extracytoplasmic) end of the invariant chain. The invariant chain-specific monoclonal antibody, VIC-Y1, was found to bind a determinant located between amino acids 1 and 73, which correspond to mainly cytoplasmic residues. Using the C-terminal specific antibodies, the number of antibody binding sites on the surface of two B lymphoma lines was estimated to be 10(5) per cell. The results of this study appear to resolve the highly disputed question of whether or not the invariant chain can appear as a plasma membrane protein. The results are discussed in the context of a possible role for the invariant chain in antigen processing and presentation.
Institute of Immunology and Genetics, German Cancer Research Centre, Heidelberg.
C J
CJ
Wraight
P
P
van Endert
P
P
Möller
J
J
Lipp
N R
NR
Ling
I C
IC
MacLennan
N
N
Koch
G
G
Moldenhauer
D000911:Antibodies, Monoclonal; D001402:B-Lymphocytes / Q000276:immunology; D001666:Binding Sites, Antibody; D015153:Blotting, Western; D002051:Burkitt Lymphoma; D002462:Cell Membrane / Q000276:immunology*; D004247:DNA / Q000235:genetics; D000939:Epitopes / Q000032:analysis; D004926:Escherichia coli / Q000235:genetics; D005434:Flow Cytometry; D015870:Gene Expression; D000949:Histocompatibility Antigens Class II / Q000032:analysis* / Q000235:genetics; D006801:Humans; D007163:Immunosorbent Techniques; D007943:Leukemia, Hairy Cell; D016403:Lymphoma, Large B-Cell, Diffuse; D011993:Recombinant Fusion Proteins / Q000276:immunology; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D000939:Epitopes; D000949:Histocompatibility Antigens Class II; D011993:Recombinant Fusion Proteins; D004247:DNA