Autoimmune response to proteasome activator 28alpha in patients with connective tissue diseases.
OBJECTIVE
To determine the autoimmune response against proteasome activator 28alpha (PA28alpha) in patients with various connective tissue diseases, and to compare the immunoreactivity between anti-PA28alpha and anti-Ki antibodies.


METHODS
Serum samples were obtained from 219 patients with various connective tissue diseases. cDNA encoding full-length human PA28alpha and Ki were produced by polymerase chain reaction. Antigens were expressed as glutathione S-transferase (GST) fusion proteins. The immunoreactivity of serum for PA28alpha and Ki was studied by Western blotting. An inhibition test was performed by ELISA using purified Ki antigen.


RESULTS
Anti-PA28alpha> antibody was detected in serum from 23% of patients with systemic lupus erythematosus (SLE) and 24% with Sjögren's syndrome (SS). These rates were significantly higher than those for the other rheumatic diseases. Since both PA28alpha and Ki are elements of the PA28 complex and their amino acid sequences share 40.2% homology, immunoreactivity to PA28alpha was studied further. Among 27 anti-Ki positive serum samples, 13 samples (48%) also reacted with PA28alpha, suggesting a relationship between anti-PA28alpha and anti-Ki antibodies. To investigate whether this finding was due to the presence of cross-reacting epitopes for PA28alpha and Ki antigens, an inhibition test was performed by ELISA. The reactivity to purified Ki antigen was not inhibited by preincubation with recombinant PA28alpha.


CONCLUSIONS
Detection of anti-PA28alpha antibody was significantly higher in serum from patients with SLE and SS. The relationship between anti-PA28alpha and Ki antibodies suggests the importance of an antigen-driven system in the induction of an autoimmune response to PA28 complex.
Matsushita
Masakazu
M
Department of Internal Medicine and Rheumatology, Juntendo University School of Medicine, Tokyo, Japan. m-matsu@fa2.so-net.ne.jp
Takasaki
Yoshinari
Y
Takeuchi
Ken
K
Yamada
Hirofumi
H
Matsudaira
Ran
R
Hashimoto
Hiroshi
H
D000918:Antibody Specificity; D001323:Autoantibodies / Q000097:blood; D001324:Autoantigens / Q000276:immunology; D003546:Cysteine Endopeptidases / Q000276:immunology*; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000276:immunology*; D009097:Multienzyme Complexes / Q000276:immunology*; D009124:Muscle Proteins / Q000276:immunology*; D009687:Nuclear Proteins / Q000276:immunology; D046988:Proteasome Endopeptidase Complex; D011506:Proteins / Q000276:immunology*; D011994:Recombinant Proteins / Q000276:immunology; D012859:Sjogren's Syndrome / Q000276:immunology*
D001323:Autoantibodies; D001324:Autoantigens; C099558:Ki antigen; D009097:Multienzyme Complexes; D009124:Muscle Proteins; D009687:Nuclear Proteins; C085047:PSME1 protein, human; D011506:Proteins; D011994:Recombinant Proteins; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex