Clinical significance of anti-multiple nuclear dots/Sp100 autoantibodies

Autoantibodies against discrete variable-sized dots observed in HEp2 cells by indirect immunofluorescence (IIF) test, called multiple nuclear dots (MND), have been closely associated with primary biliary cirrhosis (PBC). Some authors have argued that this antibody is also present in connective tissue diseases or liver diseases other than PBC as autoimmune chronic active hepatitis, particularly of the cholestatic type. We studied an unselected group of patients routinely tested for autoantibodies and positive for the MND pattern and tried to establish the correlation between the presence of this antibody and their diagnosis.

A commercial ELISA test, using a recombinant 26 kD truncated sequence of the Sp100 protein, corresponding to an immunodominant molecular region, was used to assess the clinical correlation of these autoantibodies in 110 patients showing an anti-MND immunofluorescence pattern.

One-hundred-and-ten patients were MND positive by IIF. Of these, 100 were Sp100 positive by ELISA. In the Sp100 positive group, 34 had a diagnosis of PBC (30 definite and 4 suspected) while 15 patients had a non-PBC hepatopathy. Unexpectedly, 13 of the MND/Sp100 positive pattern corresponded to systemic lupus erythematosus (SLE) patients and 5 cases to collagen diseases. Another divergence with previous reports was that 34 of the positive patients showed very heterogeneous clinical pictures, different from hepatopathies or collagen diseases.

Anti-Sp100 antibodies can be found in many clinical conditions. Testing for MND/Sp100 positivity is useful for the diagnosis of PBC, but only when the right clinical context is present. Other diseases cannot be excluded in first line SLE.