Sp100 nuclear antigen is an interferon stimulated antigen found in the bile duct of primary biliary cirrhosis. Histologically sp100 'dots' regions of the cell nucleus. Viral infection and mitogens affect the expression of the Sp100 autoantigen. Cells grown in the presence of interferons (α, β, and γ) revealed an increase both in size and number of the Sp100 protein-containing nuclear dots and increase the protein concentration. This raises "the question whether cytokine-mediated increase of Sp100 protein expression plays a role in induction of anti-Sp100 autoantibodies."

Anti-sp100 antibodies are found in association with primary biliary cirrhosis. The autoimmune target of anti-sp100 is the sp100 nuclear antigen which was identified by its association with primary biliary cirrhosis. 20-30% of patients suffering from primary biliary cirrhosis sp100 Abs.