IMMUNOLOGICALLY RESTRICTED AND INHIBITORY ANTI-RO SSA IN MONOZYGOTIC TWINS/

A pair of monozygotic twins with Sjogren's syndrome are described who both have large amounts of anti-Ro/SSA in their sera by ELISA, but no precipitin in double immunodiffusion. Unique among previously encounte red specimens, sera from the twins inhibit the formation of Ro/SSA-pre cipitins in double immunodiffusion by known anti-Ro/SSA positive SLE p atients. The twins have near identical, clonally restricted anti-Ro/SS A autoantibodies as evaluated by isoelectric focusing and bind the sam e 60 kD Ro/SSA peptides. Thus, this pair of monozygotic twins has an i dentical fine specificity in their immune response to 60 kD Ro/SSA, de spite potential differences in their immune response generated by rand om processes in the formation of immunoglobulin molecules and T cell r eceptors. These data imply that the anti-Ro/SSA found in these sera bi nds less than three epitopes such that soluble antigen/antibody comple xes are formed instead of an insoluble complex that precipitates.