We recently identified a new protein, pituitary gland specific factor 1a (PGSF1a), that is specifically transcribed in the pituitary gland. In our investigation of anti-PGSF1a antibody for pituitary diseases, we examined it in patients with RA and other autoimmune diseases. We unexpectedly discovered the frequent existence of anti-PGSF1a antibody in patients with RA. We therefore examined the prevalence of this antibody to understand its clinical significance in RA.
Anti-PGSF1a antibody was detected by radioligand assay using recombinant (35)S-labelled PGSF1a protein. Antibody activity is expressed as an index that was obtained by comparison with normal pooled serum.
RA patients had a significantly higher mean anti-PGSF1a antibody index (n=46, 1.28+/-0.38, P < 0.001) than healthy controls (n=36, 1.04+/-0.13). Indices greater than the cut-off value (mean+2 S.D. of healthy controls) were found in 43.5% (20/46) and 10.0% (2/20) of patients with RA and osteoarthritis, respectively. There was no correlation between the activities of anti-PGSF1a antibodies and titres of rheumatoid factor (RF) or serum C-reactive protein concentrations, but RA patients with more erosive disease had a higher mean anti-PGSF1a antibody index. Four of eight sera samples obtained from RF-negative RA patients were positive for anti-PGSF1a antibodies.
Anti-PGSF1a antibody is a useful new marker for the diagnosis of RA, especially for RF-negative RA, and may relate to clinical manifestations of RA.