Detect antibodies associated with SLE and mixed connective tissue disease. Sm antibodies are highly specific for SLE. RNP antibodies are found with a variety of rheumatoid diseases. RNP, Sm, SS-A, SS-B, Scl-70, and Jo-1 are extractable nucleoprotein complexes found in the nucleus and/or cytoplasm of substrate cells. Autoantibodies to the ribosomal P protein represent a highly specific marker for the diagnosis of SLE, where they have been associated with certain clinical manifestations. The native protein SmRNP contains two different regions: Sm and RNP that are different regions of the same macromolecule. SmRNP is the best antigen for detection of antibodies to either Sm or RNP but cannot discriminate between the antibody specificities. Inclusion of SmRNP increases sensitivity while inclusion of Sm and RNP increases specificity.