ANTIBODIES TO SMALL RIBONUCLEOPROTEIN AND TO 73-KD HEAT-SHOCK PROTEIN- 2 DISTINCT MARKERS OF MIXED CONNECTIVE-TISSUE DISEASE

We set out to discover whether antibodies to small ribonucleoprotein a ntigens (RNP) and to 73-kD heat shock protein (hsp 73) which have been proposed as markers of mixed connective tissue disease (MCTD) recogni ze different epitopes. MCTD serum was immunoadsorbed on hsp 73-coupled Sepharose and the affinity retained, and non-retained fractions were checked by immunoblotting for recognition of either purified bovine hs p 73 or calf thymus extract RNPs. The hsp 73 affinity-bound serum frac tion recognized hsp 73 but not RNP antigens, the reverse being true fo r the non-retained fraction. We conclude that anti-hsp 73 and anti-RNP s are distinct markers of MCTD.