Immunoblotting profiles in 55 systemic lupus erythematosus sera lacking precipitating antibodies to extractable nuclear antigens.

Serum samples from 55 patients with systemic lupus erythematosus (SLE) were selected for the absence of anti-extractable nuclear antigen antibodies after routine immunodiffusion tests. These sera were immunoblotted for anti-Sm and anti-RNP antibodies on a HeLa cell nuclear extract. Ten (18%) were negative and 45 (82%) produced complex patterns: 10 (18%) suggestive of anti-Sm, three (5%) anti-RNP, and 32 (58%) a combination of anti-Sm and anti-RNP antibodies. These data were very similar to those obtained from sera from a control group of 28 SLE sera selected for positivity of anti-Sm and anti-RNP precipitins with the immunodiffusion test. IgM isotype antibodies to the D peptide were significantly more prevalent than IgG isotype antibodies, whereas antibodies to the 68 kD polypeptide were of both IgM and IgG isotypes. Sera with an anti-Sm/RNP immunoblotting pattern stemmed from a group of patients with SLE with a higher titre of anti-dsDNA antibodies. Among clinical symptoms, the incidence of haemolytic anaemia was higher in the group of patients with the anti-Sm immunoblotting profile. Patients with an anti-RNP immunoblotting profile showed a higher incidence of cutaneous symptoms. It is concluded that immunoblotting for anti-Sm or anti-RNP antibody determination is a very sensitive diagnostic tool in patients with SLE.