Intramolecular epitope spreading in Heymann nephritis

Area of Science:

• Nephrology
• Immunology
• Molecular Biology

Background:

• Active Heymann nephritis, induced by immunization with megalin, models human idiopathic membranous glomerulonephritis.
• Megalin, a protein target, has four ligand-binding domains (LBDs) that may harbor pathogenic epitopes.
• A specific N-terminal fragment (L6) of megalin induces autoantibodies and severe disease.

Purpose of the Study:

• To investigate the epitope-specific contributions to the pathogenesis of active Heymann nephritis.
• To understand the role of intramolecular epitope spreading in the development of autoimmune kidney disease.

Main Methods:

• Immunization of rats with the L6 megalin fragment.
• Western blot analysis of rat sera reactivity against megalin fragments (L6, LBD II, III, IV).
• Monitoring of proteinuria levels in vivo.

Main Results:

• Sera from rats initially showed reactivity only to the L6 fragment.
• After 8 weeks, sera reacted with all four megalin fragments (L6 and LBDs II, III, IV).
• The L6 immunogen did not contain epitopes causing reactivity to other LBD fragments, indicating intramolecular epitope spreading.
• Increased proteinuria temporally correlated with the appearance of antibodies to LBD fragments.

Conclusions:

• B cell epitope spreading is implicated in the antibody-mediated pathogenesis of active Heymann nephritis.
• This model is valuable for studying autoimmune dysregulation in kidney disease.