A patient with systemic lupus erythematosus (SLE) has high-titre anti-dsDNA antibodies detected by Crithidia luciliae immunofluorescence. Which mechanism directly explains why anti-dsDNA antibodies are highly specific for SLE compared to other ANA-positive conditions?

• A Anti-dsDNA antibodies specifically arise from molecular mimicry with alpha-actinin in glomerular mesangial cells, and their production is driven by defective clearance of apoptotic bodies exposing nuclear antigens in a context of type I IFN amplification ✓
• B Anti-dsDNA antibodies result from Epstein-Barr virus EBNA-1 peptide cross-reactivity with RNP particles exclusive to SLE
• C Anti-dsDNA antibodies are exclusively produced by plasma cells in the germinal centre of lupus-affected lymph nodes, not found in other autoimmune disorders
• D Anti-dsDNA antibodies develop specifically because SLE patients have a germline deletion in the DNASE1L3 gene preventing extracellular dsDNA clearance

Explanation

Anti-dsDNA antibody specificity for SLE is explained by the unique constellation of defective apoptotic cell clearance (due to impaired DNase I, C1q deficiency, MFG-E8 deficiency) and type I interferon amplification driven by cytoplasmic nucleic acid sensors (cGAS-STING, TLR9). The exposed nuclear antigens during apoptosis are presented to autoreactive B cells that, in the context of T-cell help and type I IFN, undergo somatic hypermutation to generate high-affinity anti-dsDNA antibodies. Molecular mimicry with alpha-actinin contributes to their nephritogenicity. DNASE1L3 mutations are seen in familial SLE-like syndromes but are not the universal SLE mechanism. Anti-Sm antibodies (not anti-dsDNA) arise from EBNA-1 cross-reactivity (SRSF1 peptide).

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.