PCNA and autoimmune disease: In this study, we first screened for the 12 antigens specific to clinical autoimmune diseases, including MD1, SMD2, SMD3, proliferating cell nuclear antigen, acidic ribosomal phosphoprotein (P)-1, P2, SnRNP-B/B’, U1-snrnp A, U1-snrnp C, U1-SnRNP 68/70 KDa, DNA topoisomerase 1 (full length), and DNA topoisomerase 1 (truncated).