[Epitope mapping of anti-glomerular basement membrane antibodies]

To map the epitopes of anti-glomerular basement membrane (GBM) antibodies and to study their clinical relevance.

33 sera from patients with anti-GBM antibody mediated diseases were applied to inhibit monoclonal antibody against alpha 3 (IV) NC1 (Mab3), monoclonal antibody against alpha 5 (IV) NC1 (Mab5) and affinity purified, horseradish peroxidase conjugated, human anti-GBM antibodies (APab-HRP) in competitive inhibitory ELISA system using soluble human GBM proteins as solid phase ligands. The inhibition rates were evaluated in epitope mapping and used in comparison for patients with different clinical manifestations.

All 33 sera inhibited Mab3, 30/33 sera inhibited APab-HRP, and 11/33 inhibited Mab5. However, the inhibition rates were not parallel. The mean inhibition rate for APab-HRP was 55% in 27 patients with anti-GBM antibody only and was 32% in 6 patients with both anti-GBM antibody and ANCA with a significant difference (P = 0.01). For patients with or without pulmonary hemorrhage, no significant differences could be found in the mean inhibition rates for Mab3, Mab5 or APab-HRP (P < 0.05).

The anti-GBM antibodies from all patients in the present study recognize the common major epitopes on alpha 3 (IV) NC1, however, the epitopes recognized by different anti-GBM antibodies were not exactly the same. Only a small number of anti-GBM antibody positive sera recognizes alpha 5 (IV) NC1. The epitopes recognized by sera from patients with or without ANCA might be different.