Tissue-specific distribution of the Goodpasture antigen demonstrated by 2-D electrophoresis and Western blotting

The target of autoantibodies in Goodpasture's disease, the Goodpasture antigen has recently been characterized as the NC1 domain of the α3 chain of type IV collagen. In order to study the Goodpasture antigen in different organs, NC1 domains were isolated from basement membranes (BM) of human glomeruli (GBM), tubules (TBM), alveoli (ABM), placenta (PBM) and aorta (VBM). NC1 preparations were separated by 2-D electrophoresis, and silver stained or immunoblotted to determine the subunit structure and antigenicity of different basement membranes. All basement membranes contained monomeric components of MW 26 kDa and 24 kDa, and associated dimers, corresponding to the 2-D location of α1(IV) and cc2(IV) chains respectively. However, GBM, ABM, and to a lesser extent TBM possessed an extra set of monomeric components of MW 28 kDa and associated dimers corresponding to the proposed location of α3(IV) and α4(IV) chains. 2-D-separated polypeptides were Western blotted with autoantibodies from patients with Goodpasture's disease, a monoclonal antibody to the Goodpasture antigen (P1) and a monoclonal antibody to the bovine α3(IV) chain. The predominant binding of all these reagents was to cationic 28 kDa monomers of GBM, ABM and TBM, corresponding to the 3(IV) chain, although autoantibodies and P1 also bound to neutral 28 kDa monomers, corresponding to the α4(IV) chain. Autoantibodies bound weakly to more neutral components of PBM and VBM, but neither monoclonal antibody bound to these basement membranes. This study suggests that there are two separate type IV collagen networks: one containing the αl(IV) and α2(IV) chains appears to be present in all basement membranes, and the other containing the α3(IV) and α4(IV) chains has a tissue specific distribution. The latter network bearing the Goodpasture antigen is expressed in the basement membranes of both kidney and lung, the organs involved in Goodpasture's disease.