Anti-Sm autoantibodies of systemic lupus erythematosus cross react with dietary plant proteins.

Cross reactivity of patient lupus autoantibodies to the small nuclear ribonucleoprotein particles of many different types of animals is well documented. The aim of our research was to determine if any level of cross reactivity existed between proteins of common dietary plants and anti-Sm autoantibodies of lupus patient's sera, as has been found for scleroderma patient sera (Agris et al., Exptl. Cell Res. 189, 276-279, 1990). Protein extracts from soy bean, corn, spinach, and carrot were analyzed. At least one protein (molecular weight approximately 28,000 daltons) common to all the above protein extracts was recognized by most of the anti-Sm sera tested. Affinity purified antibody eluted from the 28 kilodalton plant protein specifically recognized the Sm proteins of a HeLa cell protein extract. Recognition of the 28 kilodalton dietary plant protein was found to be unique to anti-Sm lupus sera.