Although the Yale lupus sera did not immunoprecipitate BtRo60, the Western blots showing patient sera binding to BtRo60 may be biologically relevant, because binding of hRo60 antibodies to the human protein can occur in the absence of Y RNAs (35, 36). Thus, Ro60 antibodies may exist that cross-react with only the YrlA RNA-free form of the BtRo60..