In systemic lupus erythematosus, the autoantibody most frequently present is directed against which antigen?

• A. Surface antigens of bone marrow stem cells
• B. Surface antigens of renal cells
• C. Nuclear antigen
• D. Myelin

Answer: (C)

Systemic lupus erythematosus is driven by autoantibodies that target components inside cells, especially the nucleus. The most frequently detected antibodies are anti-nuclear antibodies, which bind nuclear antigens such as DNA, histones, and ribonucleoproteins. This is why the ANA test is commonly positive in SLE and reflects the characteristic humoral autoimmune response. While there are specific nuclear targets with particular associations (for example, anti-dsDNA with kidney involvement), the common and defining feature is antibodies against nuclear antigens. Antibodies against surface antigens of renal cells or bone marrow stem cells, or against myelin, are not typical features of SLE.