title: Binding of tumor necrosis factor alpha to activated forms of human plasma alpha 2 macroglobulin.
abstract: We tested the hypothesis that human plasma alpha 2 macroglobulin (alpha 2M) is a latent binding glycoprotein for human tumor necrosis factor alpha (TNF-alpha). Human recombinant 125I-TNF-alpha was incubated for 2 hours (37 degrees C) with purified native alpha 2M and with alpha 2M that was modified by reaction with methylamine or various proteinases. 125I-TNF-alpha/alpha 2M complexes were detected by nondenaturing polyacrylamide gel electrophoresis after autoradiography or by liquid chromatography on Superose-6. 125I-TNF-alpha bound strongly but noncovalently to alpha 2M-plasmin and alpha 2M-methylamine. There was minimal binding of 125I-TNF-alpha to native alpha 2M, alpha 2M-trypsin, or alpha 2M-thrombin. A 10(6) molar excess of porcine heparin did not reduce the binding of 125I-TNF-alpha to alpha 2M-methylamine or alpha 2M-plasmin. alpha 2M-plasmin or alpha 2M-methylamine added to human plasma or serum preferentially bound 125I-TNF-alpha in the presence of native alpha 2M. 125I-TNF-alpha also bound to 'fast' alpha-macroglobulins in methylamine-reacted human, rat, mouse, swine, equine, and bovine plasma. However, TNF-alpha, preincubated with either alpha 2M-plasmin or alpha 2M-methylamine, remained a potent necrogen for cultured L929 cells. Purified 125I-TNF-alpha/alpha 2M-plasmin complex injected intravenously in CD-1 mice rapidly cleared from the circulation, unless the alpha 2M-receptor pathway was blocked by coinjection of excess alpha 2M-trypsin. These findings demonstrate that alpha 2M is a latent plasmin-activated binding glycoprotein for TNF-alpha and that TNF-alpha/alpha 2M-plasmin complexes can be removed from the circulation by the alpha 2M-receptor pathway. This suggests that alpha 2M may be an important regulator of the activity and distribution of TNF-alpha in vivo.
authors.affiliation: Department of Pathology, University of Guelph, Ontario, Canada.
authors.forename: G K
authors.initials: GK
authors.lastname: Wollenberg
authors.forename: J
authors.initials: J
authors.lastname: LaMarre
authors.forename: S
authors.initials: S
authors.lastname: Rosendal
authors.forename: S L
authors.initials: SL
authors.lastname: Gonias
authors.forename: M A
authors.initials: MA
authors.lastname: Hayes
mesh_terms: D000818:Animals; D001769:Blood / Q000378:metabolism; D002417:Cattle; D002460:Cell Line; D010450:Endopeptidases / Q000494:pharmacology; D006801:Humans; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008744:Methylamines / Q000494:pharmacology; D011971:Receptors, Immunologic / Q000502:physiology; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*; D000511:alpha-Macroglobulins / Q000378:metabolism*
chemical_list: D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008744:Methylamines; D011971:Receptors, Immunologic; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D000511:alpha-Macroglobulins; C027451:methylamine; D010450:Endopeptidases