Characterization of a Soluble Nuclear Ribonucleoprotein Antigen Reactive with Sle Sera

Abstract A soluble nuclear ribonucleoprotein antigen reactive with SLE sera in precipitin and complement fixation reactions is described. The antigen was shown to be quite labile and was not recovered from human autopsy material (liver and spleen) but was easily demonstrated in extracts of surgically removed human thymoma and thymus, as well as in extracts of human chronic myeloid leukemia and normal bone marrow cells. It could also be extracted from calf thymus tissue and the thymus and spleen of the rabbit. It was characterized as ribonucleoprotein because the antigenic activity was destroyed by both ribonuclease and trypsin and the washed immune precipitate contained material which yielded an orcinol reaction product with an absorption spectrum indistinguishable from ribose. The antigen was found to be unstable at relatively moderate temperatures (40°C), at pH below 5.0 and above 9.0, and was destroyed by treatment with sodium metaperiodate. Antibodies to this antigen, designated Mo, were found in a high proportion of SLE sera and were absent from a variety of sera from patients with other connective tissue diseases as well as normal sera. The nuclear fluorescent pattern associated with this system was shown to be “speckled.”