Cross-reaction between antibodies to the major epitope of Ro 60 kD autoantigen and a homologous peptide of Coxsackie virus 2 B protein

Coxsackie virus RNA has recently been detected in biopsy specimens of minor salivary glands from patients with primary Sjögren’s Syndrome (pSS). A peptide derived from Coxsackie virus 2B protein (pepCoxs) presents 87% sequence homology with the 222–229 region of the major linear B-cell epitope of Ro60 kD autoantigen (pep216–232). Synthetic peptides corresponding to pep216–232: ²¹⁶ KALSVETEKLLKYLEAV ²³² and pepCoxs: ³¹ MVTSTITEKL LKNLVKI ⁴⁷ , were prepared. Sera from 42 patients with pSS and 43 patients with systemic lupus erythematosus (SLE) as well as sera from 27 healthy individuals (normal controls) and sera from 30 patients with rheumatoid arthritis (disease controls) were tested against the two homologous peptides. Twenty-five percent of SLE sera and 33·3% of pSS sera reacted against pep216–232, whereas 28% of SLE sera and 37% of pSS sera recognized the pepCoxs. The sera reacting with pep216–232 were apparently the same as those reacting with pepCoxs. Normal sera and disease control sera presented only a limited reactivity against both peptides (ranging from 3·7% to 10%). Both peptides reacted more prominently with anti-Ro/La (+) sera from pSS patients. Thus, pep216–232 was recognized by 17% of the anti-Ro (+) sera and by 42% of the anti-Ro/La (+ ) sera, whereas pepCoxs was recognized by 28·5% and 38% of the a-Ro(+) and a-Ro/La(+) sera, respectively. Purified antipep216– 232 antibodies readily reacted with both peptides while inhibition experiments revealed the specificity of this reaction. These results suggest a possible cross-reaction between antibodies to the major linear B-cell epitope of Ro60 kD autoantigen and the homologous pepCoxs in pSS patients. This cross-reaction might potentially play a role in autoantibody formation and the perpetuation of the autoimmune response against Ro/SSA and La/SSB.