title: Evidence for the binding of human serum amyloid P component to Clq and Fab gamma.
abstract: In order to clarify the mechanism of interaction of serum amyloid P component (SAP) with complement, the interaction of SAP with C1q and with IgG was studied. It is known that SAP binds Sepharose in the presence of calcium. When purified 125I-C1q was incubated with SAP prior to Sepharose affinity chromatography, 125I-C1q was retained. However, in the absence of SAP, the 125I-C1q was not retained. To further examine the interaction of SAP with C1q, isolated SAP was incubated at varying ratios with C1q in the presence of 1.5 mM Ca2+. These mixtures were subsequently examined via crossed immunoelectrophoresis against goat anti-SAP. A change in the electrophoretic behavior of SAP was observed in the presence of C1q. In other studies, it was observed that SAP might interact with the collagen-like stem of C1q. In these latter studies, 125I-SAP was incubated with pepsin digests of C1q in a microtitre solid-phase binding assay. In addition, a microtitre solid-phase binding assay was utilized in order to investigate the possible binding of isolated 125I-SAP with IgG. Interestingly in the presence of Ca2+, human IgG and Fab gamma, but not Fc gamma, were found to bind 125I-SAP.
mesh_terms: D000937:Antigen-Antibody Reactions; D003166:Complement Activating Enzymes / Q000276:immunology*; D015922:Complement C1q; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000276:immunology*; D007074:Immunoglobulin G / Q000276:immunology; D007143:Immunoglobulin Heavy Chains / Q000276:immunology*; D007142:Immunoglobulin gamma-Chains / Q000276:immunology*; D000683:Serum Amyloid P-Component / Q000276:immunology*
chemical_list: D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G; D007143:Immunoglobulin Heavy Chains; D007142:Immunoglobulin gamma-Chains; D000683:Serum Amyloid P-Component; D015922:Complement C1q; D003166:Complement Activating Enzymes