Human autoantibody recognition of DNA

Area of Science:

• Immunology
• Molecular Biology
• Autoimmunity

Background:

• Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by autoantibodies, including those targeting DNA.
• The development of high-affinity autoantibodies is often associated with somatic hypermutation of antibody genes.

Purpose of the Study:

• To investigate the origin of high-affinity DNA-binding antibodies in SLE.
• To explore the role of antibody gene mutations and specific sequence features in DNA recognition.

Main Methods:

• Construction and screening of phage display libraries from SLE and healthy donors.
• Affinity selection against human placental DNA.
• Characterization of antibody fragments (Fabs) using surface plasmon resonance and DNA-binding assays.
• Analysis of antibody gene sequences, including somatic hypermutation and complementarity-determining region 3 (CDR3) sequences.
• Heavy-chain CDR3 (HCDR3) transplantation experiments.

Main Results:

• High-affinity DNA-binding Fabs were isolated from both SLE and healthy donor libraries, but predominantly from the SLE library.
• These high-affinity Fabs showed positive results in the Crithidia luciliae assay, a diagnostic marker for SLE.
• Antibody genes from high-affinity SLE Fabs exhibited minimal somatic hypermutation.
• A predominance of basic residues was observed at the N-terminus of the HCDR3 in SLE Fabs.
• HCDR3 transplantation successfully conferred DNA-binding ability to an unrelated antibody.

Conclusions:

• High-affinity DNA recognition in SLE can occur without extensive somatic hypermutation.
• The heavy-chain CDR3 (HCDR3) plays a critical role in high-affinity DNA binding.
• Specific HCDR3 sequences, potentially with basic residues, may drive autoreactivity in SLE.