Anti-Ro fine specificity defined by multiple antigenic peptides identifies components of tertiary epitopes

Anti-Ro (or SSA) is a clinically important autoantibody that is found in 25-40% of patients with systemic lupus erythematosus as well as an even greater proportion of patients with Sjögren's syndrome or subacute cutaneous lupus. We have studied the binding of anti-Ro sera to multiple antigenic peptides constructed from the sequence of the 60-kD Ro molecule. The results demonstrate that sera bind these peptides in solid-phase assay. Surprisingly, some of these peptides also form a precipitin line in double immunodiffusion with anti-Ro sera. Formation of lines of identity in double immunodiffusion as well as absorption studies indicate that peptides distant in the primary amino acid sequence and without shared sequence are bound by the same antibody. In addition, data from surface plasmon resonance demonstrate that peptides identified in this manner have protein-protein interactions. Thus, these techniques may identify the components of conformational epitopes.