Antibodies to soluble liver antigen and alpha-enolase in patients with autoimmune hepatitis.Report as inadecuate




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1 Institute of Liver Studies 2 Protéines de défense des réponses immune et inflammatoire : identification, régulation et rôles physiopathologiques

Abstract : BACKGROUND: Antibodies to a cytosolic soluble liver antigen SLA are specifically detected in patients with autoimmune hepatitis AIH. The target of anti-SLA has been identified as a ~50 kDa UGA serine tRNA-associated protein complex tRNPSerSec, through the screening of cDNA libraries. A recent report questioned the identity of tRNPSerSec as the real SLA antigen. The latter study identified alpha-enolase as a major anti-SLA target, through proteomic analysis. METHODS: In an attempt to explain the observed discrepancy we have investigated reactivity of SLA positive sera against alpha-enolase and tRNPSerSec using rat and primate liver homogenate and the recombinant antigens. Thirty-three serum samples, 11 from SLA-positive patients and 22 from SLA negative controls were investigated. SLA antibodies were detected by an inhibition ELISA and confirmed by immunoblot using human liver homogenate. Autoantibody reactivity was further evaluated using preparations of primate and rat liver homogenates. Anti-alpha-enolase antibody reactivity has been tested by immunoblot using recombinant alpha-enolase. An affinity purified goat polyclonal anti-alpha-enolase IgG antibody was used as reference serum sample. Anti-tRNPSerSec antibody reactivity was detected by ELISA or dot blot using recombinant tRNPSerSec antigen. RESULTS AND DISCUSSION: The affinity purified IgG antibody directed to human alpha-enolase gave a band of approximately 48 kDa in both human and rat liver homogenates. A high titre anti-tRNPSerSec antibody serum gave a single band of ~50 kDa in both liver preparations. All but one anti-SLA antibody positive sera reacted with a ~50 kDa but none immunofixed a 48 kDa band. All anti-SLA antibody positive sera reacted strongly with the recombinant full length tRNPSerSec protein. None of the anti-SLA negative sera reacted with tRNPSerSec. Anti-SLA positive, and anti-SLA negative sera reacted equally against recombinant alpha-enolase by immunoblot. Pre-incubation of anti-SLA positive sera with tRNPSerSec completely abolished the 50 kDa band. The findings of the present study indicate that alpha-enolase and tRNPSerSec are both expressed in primate and rat liver and have a respective MW of 48 and 50 kDa. They also show that anti-tRNPSerSec - but not anti-alpha-enolase - correlates with anti-SLA antibody reactivity. CONCLUSION: Our findings indicate that tRNPSerSec is the most likely target of anti-SLA.





Author: Dimitrios-Petrou Bogdanos - Daniele Gilbert - Ilaria Bianchi - Simona Leoni - Ragai Mitry - Yun Ma - Giorgina Mieli-Vergani - Die

Source: https://hal.archives-ouvertes.fr/



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