Anti-sp100 antibodies are found in association with primary biliary cirrhosis.[1] 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 with primary biliary cirrhosis have sp100 Abs. The sera of these patients exhibit a characteristic "nuclear dots" pattern in indirect immunofluorescence (IIF) on Hep-2 cells.