The plasma protein which inhibits complement-mediated prevention of immune precipitation is an Fc binding protein

A glycoprotein (gp60) that inhibits complement-mediated prevention of immune precipitation (PIP) has been purified from normal serum. [125I]gp60 binds to IgG but not to IgA or IgM. The binding site has been shown to be localized on the Fc piece. The binding of radiolabelled gp60 to IgG has been anal...

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Bibliographic Details
Published in:Immunology 1989, Vol.66 (1), p.20-25
Main Authors: AHMED, A. E. E, BIRD, P, MCKAY, I. C, WHALEY, K
Format: Article
Language:English
Subjects:
Antigen-antibody reactions, antigen-antibody complexes, antibody-complement and others. Study of affinity. Antigen presentation
Binding Sites
Binding, Competitive
Biological and medical sciences
Complement C1q - metabolism
Fundamental and applied biological sciences. Psychology
Fundamental immunology
Humans
Immunoglobulin Fc Fragments - metabolism
Immunoprecipitation
Molecular immunology
Protein Binding
Rheumatoid Factor - metabolism
Sialoglycoproteins - metabolism
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Summary:A glycoprotein (gp60) that inhibits complement-mediated prevention of immune precipitation (PIP) has been purified from normal serum. [125I]gp60 binds to IgG but not to IgA or IgM. The binding site has been shown to be localized on the Fc piece. The binding of radiolabelled gp60 to IgG has been analysed by direct binding and Scatchard, double-reciprocal and Hill plots. The mean affinity constant of gp60 for IgG is 1.56 x 10(8) l/mol and there appears to be a single class of binding sites for gp60 on IgG. Saturation was achieved when one molecule of gp60 was bound to each molecule of IgG. In competition inhibition assays, gp60 was shown to compete with C1q and IgM and IgG rheumatoid factors. The ability to inhibit C1q binding suggests that gp60 inhibits PIP by preventing binding and activation of C1. The possibility that gp60 is a fluid-phase Fc gamma receptor is discussed. See also the note added in proof.
ISSN:0019-2805
1365-2567