title: Interference of immunoglobulins in the radioimmunoassay of human beta-endorphin.
abstract: The interference of immunoglobulins in the radioimmunoassay (RIA) of human beta-endorphin was investigated. Human IgM showed no cross-reactivity. Human IgA showed a weak cross-reaction, but the dilution curve of IgA did not show parallelism with the standard curve of beta-endorphin, thus indicating its antigenic difference. The dilution curves of human IgG showed 0.18% displacement with respect to the human beta-endorphin standard curve, with good parallelism. Moreover, five patients with multiple myeloma of the IgG type showed falsely elevated beta-endorphin levels. We investigated the possibility that certain IgGs may be responsible for the displacement of [125I]beta-endorphin in the beta-endorphin kit. The apparent beta-endorphin level of plasma from multiple myeloma patients was markedly decreased after affinity chromatography of the serum on protein A-Sepharose. In another 3 patients with multiple myeloma, we examined IgG interference by measuring the beta-endorphin levels in their lyophilized IgG diluted with saline. The results demonstrated high values of 20.2, 25.5 and 21.2 pmol/l respectively, also showing good parallelism. These immunological parallels to human beta-endorphin verify that a part of the amino acid sequence of human IgG is similar to that of human beta-endorphin. Consequently, in the measurement of beta-endorphin with polyclonal antibody, the results may sometimes be spuriously high due to cross-reaction with IgG, e.g., in patients with IgG myeloma. To avoid IgG interference, a specific monoclonal antibody to synthetic beta-endorphin should be used rather than polyclonal antibodies.
authors.affiliation: Department of Laboratory Medicine, Kanazawa University School of Medicine, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Hashimoto
authors.forename: S
authors.initials: S
authors.lastname: Miyabo
authors.forename: M
authors.initials: M
authors.lastname: Nishibu
authors.forename: F
authors.initials: F
authors.lastname: Matsubara
authors.forename: S
authors.initials: S
authors.lastname: Migita
mesh_terms: D001774:Blood Chemical Analysis / Q000379:methods; D003429:Cross Reactions; D006801:Humans; D007070:Immunoglobulin A / Q000032:analysis; D007074:Immunoglobulin G / Q000032:analysis; D007075:Immunoglobulin M / Q000032:analysis; D007136:Immunoglobulins / Q000032:analysis*; D011863:Radioimmunoassay / Q000379:methods*; D001615:beta-Endorphin / Q000097:blood*
chemical_list: D007070:Immunoglobulin A; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D007136:Immunoglobulins; D001615:beta-Endorphin