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.

Crude extracts of acidic nuclear proteins (extractable nuclear antigens; ENA) are routinely used as the coating antigens in hemagglutination assays for certain antinuclear antibodies. Sera of almost all patients with mixed connective tissue disease (MCTD)

The spatial organization of two rheumatic disease-associated epitopes and the RNA "cap" structure of the U1 small nuclear ribonucleoprotein (snRNP2) was analyzed both in situ and in vitro by two independent interference immuno-assays. Sm and RNP autoantibodies, associated with systemic lupus erythematosus and mixed connective tissue disease, respectively, were used to probe the epitope locations. The Sm epitope on the U1 snRNP structure was localized proximal to the RNP. Experiments with an anti-m7G (mRNA "cap") monoclonal antibody revealed that an in situ association of the Sm and RNP epitopes with the mRNA "cap" structure may exist. Our findings, together with previous observations by others, suggest a model for the spatial arrangement of these rheumatic disease-associated protein epitopes, and the U1 RNA within the U1 snRNP particle.

Autoantibody of an immortalized human lymphocyte cell line, Su-2E4, derived from peripheral lymphocytes of a patient with mixed connective tissue disease, showed specific binding of the 68K polypeptide of U1 small nuclear RNP (snRNP) and immunoprecipitation of U1 RNA. The reaction patterns of Su-2E4 and a murine monoclonal anti-(U1)snRNP line, 2.73, and results of a competition assay with the 2 antibodies suggest similar, but not necessarily identical, epitope recognition.Autoantibodies to nuclear and cytoplasmic components are frequently found in patients with systemic rheumatic diseases (1-3). The autoantigens are often nucleic acid-associated proteins, such as small nuclear RNP (snRNP) (4). Circulating autoantibodies to some of these antigens are characteristic of Presented by Jintao Chen in partial fulfillment of the requirements for a PhD degree,