Targets of Antibodies to Soluble Liver Antigen in Patients with Autoimmune Hepatitis

Antibodies to a cytosolic soluble liver antigen (SLA), originally detected by an inhibition ELISA using cytosolic liver fractions and proposed as marker of a third type of autoimmune hepatitis (AIH) negative for other autoantibodies, have been also reported in anti-nuclear and/or -smooth muscle antibody type 1 AIH, liver kidney microsomal-type 2 AIH, and autoimmune sclerosing cholangitis (1)(2)(3). Anti-SLA is specific for these autoimmune liver diseases, in which it is associated with a more severe disease course, whereas it is virtually absent in nonhepatic autoimmune disorders (1)(2)(3). The target of anti-SLA has recently been identified by several groups as a UGA serine tRNA-associated protein complex [tRNP(Ser)Sec], through the screening of cDNA libraries (4)(5)(6). On the basis that not all of the anti-SLA-positive sera identified by inhibition ELISA react with tRNP(Ser)Sec and referring to studies indicating that SLA is a mixture of distinct antigens, Ballot et al. (7) questioned the identity of tRNP(Ser)Sec as the molecular target of anti-SLA antibodies. These investigators set out to reassess the matter, using anti-SLA-positive sera against rat liver cytosolic fraction in one- and two-dimensional immunoblotting analyses. Through peptide mass fingerprint analysis after matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, the authors identified four isoforms of α-enolase, a cytosolic enzyme of 50 kDa, as the major target of … [↵][1]aAuthor for correspondence. Fax 33-1-49283046; e-mail catherine.johanet{at}sat.ap-hop-paris.fr. [1]: #xref-corresp-2-1