title: Characterization of immune complexes detected by the 125I-C1q binding assay in breast cancer.
abstract: The aim of the present study was to isolate and characterize immune complexes measured by the 125I-C1q binding assay in breast cancer sera. The C1q binding assay detects immune complexes by their binding to 125I-C1q and subsequent precipitation with PEG. We purified the C1q binding material from these precipitates by superose 6 gel filtration and cation exchange chromatography. The isolation steps were monitored by the C1q binding assay and the purified material was analyzed by SDS--PAGE and immunodiffusion. The C1q binding material isolated from two breast cancer sera contained complexes of IgM, C4b binding protein (C4-bp), and C1q. The C4-bp fraction showed significant C1q binding activity which increased after the addition of IgM. This C4-bp was not different from C4-bp isolated from normal serum. The IgM fraction, however, differed from normal IgM by its binding to C4-bp and C1q and its stronger affinity to the cation exchange column. These unique properties were not due to rheumatoid factor activity. They might be caused by a different glycosylation pattern or by complex formation with an as yet unknown polysaccharide antigen.
authors.affiliation: Department of Internal Medicine, University Göttingen, Federal Republic of Germany.
authors.forename: G
authors.initials: G
authors.lastname: Krieger
authors.forename: M
authors.initials: M
authors.lastname: Kneba
authors.forename: I
authors.initials: I
authors.lastname: Bolz
authors.forename: G A
authors.initials: GA
authors.lastname: Nagel
mesh_terms: D000912:Antibodies, Neoplasm / Q000276:immunology; D000936:Antigen-Antibody Complex / Q000032:analysis*; D000951:Antigens, Neoplasm / Q000032:analysis*; D001943:Breast Neoplasms / Q000276:immunology*; D002352:Carrier Proteins / Q000032:analysis; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D003166:Complement Activating Enzymes / Q000032:analysis*; D003172:Complement C1 / Q000032:analysis*; D015922:Complement C1q; D006801:Humans; D007075:Immunoglobulin M / Q000032:analysis; D016167:Integrin alphaXbeta2; D009363:Neoplasm Proteins / Q000032:analysis
chemical_list: D000912:Antibodies, Neoplasm; D000936:Antigen-Antibody Complex; D000951:Antigens, Neoplasm; D002352:Carrier Proteins; D003172:Complement C1; D007075:Immunoglobulin M; D016167:Integrin alphaXbeta2; D009363:Neoplasm Proteins; D015922:Complement C1q; D003166:Complement Activating Enzymes