Biochemical complexity of serum HLA class I molecules.
Human serum was found to contain a variety of class I-like molecules by Western blotting with anti-class I heavy chain reagents: major bands usually are observed around Mr 44,000, 40,000, and 35,000-37,000. HLA-A24-positive individuals are distinguished by higher serum levels of Mr 44,000 and 40,000 class I-like molecules than those found in HLA-A24-negative individuals. The Mr 44,000 serum molecules are probably intact class I molecules that have been shed from the cell membrane, because they contain both a transmembrane segment (TM), as deduced from detergent-binding experiments, and a cytoplasmic tail (CT), as inferred from reactivity with an antipeptide serum specific for the cytoplasmic domain of class I antigens (RaCT). The Mr 35,000 and 37,000 molecules contain neither a TM nor a CT region and therefore are probably proteolytic breakdown products of cellular and/or serum Mr 44,000 molecules, although the existence of Q10-like molecules in man cannot be ruled out. The Mr 40,000 molecules do not contain a TM region. Mr 40,000 molecules reactive with the RaCT serum were found in the minority (2/13) of sera tested. We conclude that alternative splicing resulting in a precise excision of the TM exon plays a minor role in the generation of serum HLA class I antigens.
Dobbe
L M
LM
Department of Immunohaematology, University Hospital, Leiden, The Netherlands.
Stam
N J
NJ
Neefjes
J J
JJ
Giphart
M J
MJ
D000818:Animals; D000937:Antigen-Antibody Reactions; D000954:Antigens, Surface / Q000276:immunology / Q000302:isolation & purification; D002478:Cells, Cultured; D003101:Collodion; D004591:Electrophoresis, Polyacrylamide Gel; D006680:HLA Antigens / Q000276:immunology / Q000302:isolation & purification*; D015789:HLA-A2 Antigen; D006649:Histocompatibility Antigens / Q000276:immunology / Q000302:isolation & purification; D015395:Histocompatibility Antigens Class I; D006801:Humans; D007163:Immunosorbent Techniques; D051379:Mice; D008970:Molecular Weight; D011817:Rabbits; D012995:Solubility; D001613:beta 2-Microglobulin / Q000276:immunology / Q000302:isolation & purification
D000954:Antigens, Surface; D006680:HLA Antigens; D015789:HLA-A2 Antigen; D006649:Histocompatibility Antigens; D015395:Histocompatibility Antigens Class I; C032907:Q surface antigens; D001613:beta 2-Microglobulin; D003101:Collodion