Autoantibodies to the Ro (SSA) antigen are one of the most frequent serological autoimmune markers in rheumatic diseases. Anti-Ro-positive sera may contain two different types of autoantibody; those directed to a 60 kDa and those directed to a 52 kDa polypeptide component (referred to as Ro60 and Ro52 respectively). While the vast majority of Ro(SSA) positive sera react with both of these components, anti-Ro60 antibody has been reported to occur without anti-Ro52 antibody only in SLE sera whereas anti-Ro52 antibody has been reported to occur in the absence of anti-Ro60 antibody in idiopathic inflammatory myopathy, dermatomyositis and scleroderma.
Antibodies to Ro52 have been observed to occur not only monospecifically or with Ro(SSA)/La(SSB), but also concurrently with antibodies to Jo-1 and to other aminoacyl transferases, with anti-SRP, anti-PMScl, anti-CENP-B, anti-RNP and antihistones. The differing serological and clinical associations of anti-Ro52 and anti-Ro60 suggest that anti-Ro52 should be considered as an additional connective tissue disease serum marker, independent of anti-Ro60(SSA).
Ro52 is a member of the tripartite motif (TRIM) family of proteins. The TRIM motif includes three zinc-binding domains, a RING finger, a B-box type 1 and a B-box type 2, and a centre coiled-coil region (leucine zipper). TRIM proteins are believed to identify specific cell compartments through a process of homo-multimerisation. Other functional studies have suggested a role for a putative leucine zipper domain of Ro52 in protein dimer formation and inhibition of transcription activity, and involvement of Ro52 in the ubiquitin pathway.
Although autoantibodies are known to bind to multiple epitopes on the Ro52 protein, the leucine zipper domain and an area on the N-terminal side of it have been shown to constitute a prominent linear epitope.
Systemic Lupus Erythematosus
Neonatal Lupus Syndrome
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