Specificity of kidney-bound antibodies in Goodpasture's syndrome

The specificity of kidney-bound antibodies in Goodpasture's syndrome was studied and compared with the specificity of circulating anti-glomerular basement membrane (GBM) antibodies. Antibodies were eluted from kidneys of two patients with Goodpasture's syndrome and from one normal human kidney. Their specificity was studied by indirect immunofluorescence microscopy, ELISA and immunoblotting using purified GBM components as antigens. It was shown that the reactivity of the eluted antibodies was very similar to those of the circulating anti-GBM antibodies. Both showed major reactivity against the M2 subunit of the globular domain of collagen IV. Competitive inhibition of the binding of 125I-labelled serum antibodies from a patient with Goodpasture's syndrome to the Goodpasture antigen by the eluted antibodies and those from their respective sera further supported that the circulating and the kidney-bound anti-GBM antibodies have similar specificity. These observations extend the support to the clinical usage of plasmapheresis and more recently, immunoadsorption using staphylococcal protein A as the effective therapeutic measure for the removal of circulating anti-GBM antibodies in the management of Goodpasture's syndrome.