Antibodies to the constitutive 73-kd heat shock protein: a new marker of mixed connective tissue disease?

Purpose, Patients, And Methods: This report documents the finding of an elevated titer of IgG reacting with the constitutive bovine 73-kd heat shock protein (HSP) in the serum of patients with rheumatoid arthritis, scleroderma, and mixed connective tissue disease (MCTD).

Results And Conclusions: Further characterization of antibodies from patients with MCTD showed that the antibodies also recognize the human constitutive 73-kd HSP, but not the inducible 72-kd isoform. Very high levels of antibodies appeared to be specific for MCTD; the differences between levels in patients with MCTD and those in healthy subjects (blood donors) were highly significant (p < 10(-8)), with no values in this group of patients overlapping with those in the controls. This parameter might therefore represent a new diagnostic marker for this disease.