Both the U1-specific proteins and the Sm core particle are targets of autoantibodies which classically have been called the RNP and RNP-Sm specificities, respectively. A clean diagnostic distinction of these specificities has been complicated by the biochemical difficulties of producing clean subparticle fractions from native sources. The use of single recombinant proteins as antigenic targets guarantees a much higher sensitivity and specificity and is the only way to determine RNP antibodies sensu stricto without the disturbing influence of Sm antigens; also with single U1 proteins antibodies will be detected which can be missed because of steric hindrance when using the RNP-Sm complex in an assay.
Autoantibodies to U1-snRNP are present in 95% of patients with Mixed Connective Tissue Disease (MCTD) and 30% of patients with SLE. Antibodies against the 68/70 kDa protein are known to have a high clinical significance in MCTD patients. The 68/70 kDa nomenclature of this protein refers to the fact that different splice variants of the protein are found in human cells.
The Calculated molecular weight is 44.8 kDa (U1-snRNP 68 displays aberrant electrophoretic mobility leading to an apparent discrepancy between calculated molecular weight and the 55-56 kDa molecular weight determined for this internally shortened molecule by SDS gel electrophoresis).
Store at 4°C if entire vial will be used within 2-4 weeks.
Store, frozen at -20°C for longer periods of time.
Avoid multiple freeze-thaw cycles.
0.3-0.6 µg/ml (depending on the type of ELISA plate and coating buffer). Suitable for labeling of functional groups.
Greater than 95% as determined by SDS-PAGE.
2. Standard ELISA test (checker-board analysis of positive/negative sera panels including CDC international reference sera).
Western-Blot with monoclonal anti-hexa-His-tag antibody & anti SNRP70 autoantibody positive sample.