Characterization Analysis of Human Anti-Ferritin Autoantibodies

Abstract

Anti-ferritin autoantibodies are found in many animals. Human ferritin-binding proteins (FBPs) were partially purified from human serum by ion-exchange chromatography and immobilized metal affinity chromatography with Zn 2+ . Crude FBPs were immunocoprecipitated with canine liver ferritin followed by the addition of anti-ferritin antibodies. Immunoglobulins in the immunocoprecipitate were detected with antibodies specific for human IgG, IgM or IgA heavy chains, and immunoglobulins IgG, IgM and IgA to bind to expressed recombinant human H and L chain homopolymers were also found. A portion of human serum proteins bound to zinc ions immobilized on beads were released upon the addition of canine liver ferritin, and the released protein was identified as IgM antibody. Additionally, the released proteins recognized peptide sequence (DPHLCDF) commonly found in amino acid sequences of mammalian ferritin H and L subunits. These results suggest that human serum contains anti-ferritin autoantibodies (IgG, IgM and IgA) which bind zinc ions and preferentially bind ferritin over both the H and L subunits, and that a portion of, but not all, the IgM antibodies bound to ferritin with higher affinity than to zinc ions and may recognize the common sequence found in mammalian ferritin H and L subunits.

Binding Analysis of Human Immunoglobulin G as a Zinc-Binding Protein

“…Human IgG Fab and F(c) fragments were detected by SDS-PAGE at very low levels in pelleted CB; in contrast, the F(c) fragments were strongly detected in a sample of pelleted Zn-beads but the Fab fragment was not, suggesting that the F(c) fragment is likely involved in the binding between IgG and zinc ions. Human anti-ferritin autoantibodies (IgG, IgM, IgA) bind with zinc ions [12], indicating that all classes of immunoglobulins bind zinc ions. Further studies are required to clarify the binding between zinc ions and the F(c) fragments of other mammalian IgGs, and the binding of zinc ions with other classes of human immunoglobulins.…”

“…Zinc functions as an antioxidant and anti-inflammatory agent through various mechanisms [1,2,3,4,18,19,20]. Many zinc-binding proteins are present in mammalian circulatory systems including albumin, α 2 -macroglobuin, haptoglobulin, ceruloplasmin, immunoglobulins (IgG, IgM and IgA), complement C 4 , prealbumin, C-reactive protein, and fibrinogen [9,10,11,12,13,14]. These proteins likely transport zinc ions to cells requiring zinc ions.…”

“…Homeostasis of the intracellular zinc level is strictly regulated by the zinc transporter [8]. There are many zinc-binding proteins in human blood such as albumin, α 2 -macroglobuin, haptoglobulin, ceruloplasmin, immunoglobulins (IgG, IgM and IgA), complement C 4 , prealbumin, C-reactive protein, and fibrinogen [9,10,11,12,13]. Zinc-binding proteins may act as zinc storage compounds for maintaining immunoregulatory and oxidative balance [10].…”

Metal-ligand forms of iron and zinc in the human body

“…Согласно данным Y. Yamanaka и соавт., IgG способен специфически связывать ионы цинка через домен Fc [68]. Полученные данные показывают, что молекула γ-глобулина содержит несколько сайтов связывания цинка [77,78]. Таким образом, при взаимодействии с ионами цинка, распределёнными в периглобулярном пространстве, образуются металлокомплексы, приобретающие новые эффекторные функции по сравнению с теми, которые проявляют γ-глобулины в нативной области [79].…”