Nuclear protein antigens in autoimmune rheumatic and connective tissue diseases

Two nuclear antigens, Sm and RNP, that act as markers in Systemic Rheumatic (SRD) and Connective Tissue Diseases (CTD) have been studied with regard to their composition and biochemical properties. RNP antigen appears to be a 10S nuclear RNP particle containing SnRNA. Sm antigen, formerly considered to be a protein, may also contain RNA. Although both antigens are considered to be saline soluble, evidence suggests that they are part of a nuclear structure that is only slowly dissociated under isotonic conditions.