STUDY OF EHS TYPE-IV COLLAGEN LACKING GOODPASTURES EPITOPE IN GLOMERULONEPHRITIS IN RATS

The Goodpasture's epitope has been mapped to the alpha(3) non-collagenous chain (NC1) of type (IV) collagen [alpha(3)col(IV)]. We have developed a model of experimental autoimmune glomerulonephritis (EAG) in rats immunized once with collagenase solubilized GBM (csGBM). Engelbreth-Holm-Swarm (EHS) tumor contains abundant col(IV) with little or no alpha(3)col(IV). To test the hypothesis that antigens related to Goodpasture epitope are required to produce EAG in our model, we immunized rats once with 40 mu g csEHS. Positive controls immunized with csGBM developed typical EAG with GBM bound antibody, proteinuria, and glomerulonephritis. EHS rats developed circulating and bound antibody to mesangium and tubular basement membrane with minimal GBM deposits, but did not develop proteinuria or glomerulonephritis. Although circulating antibody in EHS rats bound to csGBM by ELISA, there was no binding in ELISA to M2 antigen containing the Goodpasture epitope while EAG rat's serum did bind. By Western blot with antisera to Goodpasture epitope, EHS antigen was less complex than GBM in the monomer/dimer regions and appeared to lack NCI corresponding to alpha(3)col(IV). Blotting with sera from EHS rats demonstrated reactivity to various components of GBM but not to alpha(3)col(IV). EAG sera and renal eluates bound to alpha(3)col(IV). EAG rats evidenced cell mediated immunity while EHS rats did not (stimulation index EHS 1.1, EAG rats 8.0). These studies show that the development of antibody to col(nr) in a setting conducive to EAG does not cause EAG in the absence of alpha(3)col(TV) NC1, that the antibody response in EHS rats was not associated with a cellular response to the antigen and that an epitope on the same NC1 alpha(3)col(IV) which contains the Goodpasture epitope appears necessary to induce EAG in this model These studies further implicate the alpha(3)col(IV) as a pathogenetic factor in the development of Goodpasture syndrome in humans as well as a marker of disease.