Unique epitopes in RNA helicase II/Gu protein recognized by serum from a watermelon stomach patient

RNA helicase II/Gu (RH II/Gu) is a nucleolar antigen originally identified using an autoimmune serum from a patient with watermelon stomach. A later r eport showed that anti-RH II/Gu autoantibodies were also present at low fre quency in connective tissue disease (CTD) patients who did not show any sym ptoms suggestive of a watermelon stomach lesion. In an attempt to understan d the relationship between watermelon stomach, also called gastric antral v ascular ectasia (GAVE), and autoimmune disorder, we identified the antigeni c sites recognized by these autoantibodies. Serum Gu uniquely recognized ep itopes at amino acids 646-748 of RH II/Gu and all four CTD patient sera rec ognized antigenic sites within amino acids 1-173. Anti-RH II/Gu serum produ ced by immunizing rabbit with recombinant human RH II/Gu protein bound to t he same antigenic sites recognized by the CTD patient sera, but it did not recognize the serum Cu epitopes. Results are also presented showing the use of these anti-RH II/Gu antibodies in the analysis of the evolutionary cons ervation of RH II/Gu in human, monkey and mouse. (C) 2000 Elsevier Science Ltd. All rights reserved.