Definition of a discontinuous immunodominant epitope at the NH2 terminus of the La/SS-B ribonucleoprotein autoantigen

L J McNeilage, K Umapathysivam, Elizabeth Macmillan, A Guidolin, S Whittingham, T Gordon

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High-titer IgG autoantibodies to the La/SS-B ribonucleoprotein (RNP) are a hallmark of patients with primary Sjogren's syndrome. Anti-La/SS-B-positive human sera bind to multiple epitopes on recombinant La/SS-B, although the initial response is against an immunodominant epitope within the first 107 NH2-terminal amino acids (aa). Sequence analysis has identified a striking homology between aa 88-101 in this NH2-terminal region of La/SS-B and a feline retroviral gag polypeptide suggesting the anti-La/SS-B response may be initiated by cross-reactivity with an exogenous agent. In the present study, detailed mapping of this NH2-terminal epitope, using recombinant La/SS-B purified from the expression of overlapping DNA fragments spanning aa 1-107, has shown that this immunodominant epitope is a complex conformational or discontinuous epitope dependent upon both aa 12-28 and 82-99 for expression, even though these regions share no homology with each other. This requirement questions the significance of the homology between La/SS-B and a retroviral gag polypeptide in the generation of the B cell response to La/SS-B and is in accord with the general concept that B cells recognize conformational epitopes on antigens rather than small linear peptide sequences. The finding also reinforces the notion that native autoantigen could be the initiator of the autoimmune response.

Original languageEnglish
Pages (from-to)1652-1656
Number of pages5
JournalJournal of Clinical Investigation
Issue number5
Publication statusPublished - 1 May 1992
Externally publishedYes


  • Anti-La/SS-B
  • Autoanti-body
  • Epitope mapping
  • Molecular mimicry


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