Structural differences between the human and mouse 52-kD Ro autoantigens associated with poorly conserved autoantibody activity across species.
Anti-nuclear autoantibodies found in human autoimmune diseases frequently cross-react with homologous autoantigens in distant species, supporting the notion that autoantibodies target conserved functional domains. However, the 52-kD Ro(SS-A) protein is an exception, in that human autoantibodies are not known to recognize any equivalent antigen in the cells of rodents and other non-primate species. To understand this lack of cross-reactivity we have isolated cDNAs encoding the mouse 52-kD Ro molecule. The cDNA encoding mouse 52-kD Ro revealed an open reading frame of 470 amino acids, with 70% sequence identity to the human 52-kD Ro antigen. The putative leucine-zipper and zinc-finger motifs present in human Ro52 were conserved in the mouse protein. Recombinant mouse 52-kD Ro protein reacted with human autoantibodies by ELISA and immunoblot, but with approximately 10-fold lower reactivity than recombinant human 52-kD Ro protein under the same conditions. Detection of both human and mouse 52-kD Ro by immunoblot was dependent on antigen concentration which was limiting in the cell equivalents generally used in immunoblot assays. Differential chaotropic disruption of antibody binding suggested a lower avidity of human autoantibody binding to the mouse 52-kD Ro protein compared with the human antigen. Thus the poor reactivity of native mouse 52-kD Ro with human autoantibodies is associated with species divergence diffusely distributed throughout the primary structure of the 52-kD Ro molecule.
Keech
C L
CL
Centre for Transfusion Medicine and Immunology, Flinders Medical Centre, Bedford Park, Australia.
Gordon
T P
TP
McCluskey
J
J
D000595:Amino Acid Sequence; D000818:Animals; D000915:Antibody Affinity; D000937:Antigen-Antibody Reactions; D001323:Autoantibodies / Q000737:chemistry*; D001324:Autoantigens / Q000737:chemistry* / Q000235:genetics / Q000276:immunology*; D001483:Base Sequence; D003001:Cloning, Molecular; D003429:Cross Reactions; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D008970:Molecular Weight; D020733:RNA, Small Cytoplasmic; D012261:Ribonucleoproteins / Q000737:chemistry* / Q000235:genetics / Q000276:immunology*; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity; D000099207:SS-A Antigen
D001323:Autoantibodies; D001324:Autoantigens; D020733:RNA, Small Cytoplasmic; D012261:Ribonucleoproteins; D000099207:SS-A Antigen; C116006:RO60 protein, human