Alpha-actinin is a cross-reactive renal target for pathogenic anti-DNA antibodies.
Anti-DNA Abs commonly found in patients with systemic lupus erythematosus are thought to play an important pathogenic role in lupus nephritis. Anti-DNA Abs may contribute to renal disease by cross-reactivity with renal Ags, the identity of which remain elusive. To identify a target Ag for pathogenic anti-DNA Abs, we performed Western blotting and immunoprecipitations of mesangial cell lysates from the lupus-prone MRL-lpr/lpr mouse and a nonautoimmune BALB/c mouse with the pathogenic anti-DNA Ab R4A. We found that R4A (but not a nonpathogenic Ab mutant of R4A) binds to and immunoprecipitates a 100-kDa protein expressed on the cell surface and in lysates of MRL-lpr/lpr mesangial cells. DNase treatment of the lysate and of the R4A Ab did not effect binding, indicating that the binding of R4A to the 100-kDa protein was direct and not mediated by an antigenic bridge containing DNA. Binding was greatly diminished in BALB/c lysates, suggesting that Ag expression or availability at the level of the target organ may be a factor in determining susceptibility to lupus nephritis. Following identification of this 100-kDa protein as nonmuscle alpha-actinin, binding of R4A to alpha-actinin was confirmed by Western blot, ELISA, inhibition studies, and immunofluorescence. High titers of anti-alpha-actinin Abs were present in sera and kidney eluates of lupus mice with active nephritis. These results indicate that the nephritogenicity of some anti-DNA Abs may be mediated via cross-reactivity with alpha-actinin. Furthermore, variations in target Ag display between individuals may underlie differential susceptibility to anti-DNA Ab-induced renal disease.
Deocharan
Bisram
B
Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
Qing
Xiaoping
X
Lichauco
Juan
J
Putterman
Chaim
C
D000185:Actinin / Q000096:biosynthesis / Q000276:immunology* / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D000974:Antibodies, Antinuclear / Q000378:metabolism*; D001324:Autoantigens / Q000276:immunology / Q000302:isolation & purification / Q000378:metabolism; D001666:Binding Sites, Antibody; D001667:Binding, Competitive / Q000276:immunology; D002460:Cell Line; D002461:Cell Line, Transformed; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism; D003429:Cross Reactions; D005260:Female; D005920:Glomerular Mesangium / Q000166:cytology / Q000276:immunology* / Q000378:metabolism*; D008181:Lupus Nephritis / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008807:Mice, Inbred BALB C; D019463:Mice, Inbred MRL lpr; D008814:Mice, Inbred NZB; D008970:Molecular Weight; D011233:Precipitin Tests; D013045:Species Specificity
D000974:Antibodies, Antinuclear; D001324:Autoantigens; D000185:Actinin