Abstract
Complement fixation activity of anti-U1 RNP and Sm antibodies was studied by immunoblotting using sera from patients with mixed conective tissue disease (MCTD) and systemic lupus erythematosus (SLE). U1 RNP antigens were purified from rabbit thymus extract by affinity column. The purified U1 RNP antigen consisted of 65 KD, 36 KD, 32 KD, 26 KD, 16 KD and 11-14 KD polypeptides in SDS-PAGE. Anti-U1 RNP antibodies from patients with MCTD and SLE reacted with 65 KD, 36 KD, 32 KD, and 26 KD in immunoblotting.
When the complement fixation activity of antibodies to those polypeptides was tested in MCTD, the antibodies to 32 KD polypeptide showed the significantly stronger reaction compared with the antibodies to 65 KD and 36 KD polypeptides (p<0.01). In SLE patients, antibodies to 32 KD polypeptide showed the same reactivity, moreover complement fixation activity of antibodies to 26 KD and 16 KD polypeptides showed significantly higher (p<0.01) than those to 65 KD polypeptide. In comparison with complement fixation activity of antibodies to U1 RNP polypeptides between MCTD and SLE, the antibodies to 36 KD polypeptide from SLE patients showed higher activity than that from MCTD patients (p<0.05).
Those results suggest that anti-U1 RNP antibodies from MCTD and SLE patients may have different pathogenetic roles in relation to its complement fixation activity.
