Heterogeneity of Goodpasture's antigen

Epitope mapping of homologous and cross-reactive antigens by monoclonal antibodies to streptococcal cell membrane (mAb to SCM)

An approach to epitope mapping of a series of anti-streptococcal cell membrane (SCM) mAbs is described. Evaluations by enzyme-linked immunosorbent assay (ELISA) of one control mAb HB-35 and 13 different anti-SCM mAbs were made on homologous SCM antigen and human basement membrane antigens isolated from glomeruli (GBM) and lung (LBM). These anti-SCM mAbs were previously shown to be cross-reactive in a variety of systems with both GBM and LBM. The binding capacities were measured for all 14 mAbs on ELISA plates sensitized with SCM antigen or the cross-reactive GBM or LBM antigens, at 5 micrograms/ml or approximately 20 pM/well. From the 50% binding capacity dilution the pM of mAb bound/pM antigen-well was calculated which translated into an estimate of the ratio-number of epitopes bound. Observations with the homologous and cross-reactive antigens showed multiple reactive epitope ratios to eight mAbs whereas the other five yielded a ratio value of one or two on the tested antigens. Plates blocked with a specific dilution of one mAb evaluated the binding by a second mAb providing both binding and specificity data. One mAb (I-F-3) blocked all the other anti-SCM mAbs on all three antigen plates. An additive effect was noted by three mAbs, I-G-8, II-C-4 and II-D-8 with most of the other mAbs. The order of placement, however, made distinctive differences; II-F-4 showed an additive or enhancement effect on I-B-5 but no reciprocal effect was seen. A similar effect was made with I-G-8 and II-C-4 or I-F-7. Possible interpretations are that each mAb is binding different epitopes each fully exposed, and the order of placement of the mAbs makes no difference. Where an enhanced effect was observed it is suggested that the binding of the first mAb changed the conformation of the antigen, thereby opening and exposing additional epitope(s) to the second antibody. Or, in contrast, where the second mAb was blocked by the first, a fixing of the protein conformation is suggested thereby occluding the other epitope, as seen with I-F-3 and II-C-4. These epitope mapping procedures confirmed that all 13 anti-SCM mAbs were binding at different epitopes. The nature of basement membrane collagens and how this relates to post-streptococcal sequelae will be discussed.

Localization of [14C] labeled anti-streptococcal cell membrane monoclonal antibodies (anti-SCM mAb) in mice

Six different hybridomas secreting anti-SCM mAb and one control mAb were placed into adult mice along with [14C] amino acids for biosynthetically labeling. After sacrifice, the 14C mAb ascites along with serum, heart, kidney, lung and skeletal muscle were recovered. Tissue associated specific radio-activity (SpAc) and microscopic structural analyses were performed. Confirmation of mAb specificity was by both immunodot blots as well as Western blot analysis. Peritoneal injection of measured doses of anti-SCM mAb yielded tissue SpAc confirming their in vitro specificities. Two of the mAb showed strong reactivity to both renal (GBM) and lung basement membrane (LBM), two were mainly GBM reactive and two showed polyreactivity with a marked reactivity to a Z-line antigen. Autoradiographic light microscopy confirmed that the anti-SCM mAbs bound to both GBM and LBM and to Z-line antigen. Titrated doses of the mAb yielded autoradiographic confirmation in which the grain number on the GBM and LBM increased with increasing dose of mAb for all mAb except the control. This effect was not seen in the muscle tissues but anatomical localization at the Z-line was consistent. The major significance of these studies is the demonstration that circulating antibodies to SCM can react in vivo with normal mammalian antigens adding confirmation to the in vitro specificity of these cross-reactive anti-SCM mAbs.

Hybridomas to specific streptococcal antigen induce tissue pathology in vivo; autoimmune mechanisms for post-streptococcal sequelae

A gross examination of organs from approximately 100 mice which were producing ascites fluids toward a series of streptococcal reactive monoclonal hybridomas showed, in some animals, what appeared to be autoimmune-like findings. A pattern of major lung pathology was associated with specific clones. These specific hybridomas led to the development of an experimental autoimmune animal model mimicking a Goodpasture's syndrome. Tissue injury was induced in mice, on a dose dependent basis, by the injection of monoclonal antibody generated against streptococcal cell membrane (SCM) antigens. A more severe onset of the pathology, also on a dose dependent bases, was induced by placement of the anti-SCM mAb secreting hybridoma cells into the peritoneal cavity of the host. Severity of observed lesions was dependent upon the number of cells injected (10(5), 5 x 10(5), 10(6) or 10(7], as well as the animals' sex. Severe and total hemorrhagic lungs were seen in animals challenged with 1 x 10(6) hybridomas cells when sacrificed on the tenth day. In all cases the lesions were greater in the female litter mate than the male. Gross and histologic observations were confirmed by lung/body weight ratios. Pulmonary hemorrhage ranged from slight, when mAb was injected at a low dose of 24 micrograms/g, to severe when 96 micrograms/g was injected. Reported findings were based on the review of approximately 300 mice. Immunochemical evaluations and ELISAs confirmed the ability of these anti-SCM mAb to react with glomerular basement membrane (GBM) antigens as well as lung basement membrane (LBM). Mitogenic experiments indicated that the parent immunogen (SCM) used to generate immunocytes was non-stimulatory to lymphocytes.

The development of anti-glomerular basement membrane nephritis in two children with Alport's syndrome after renal transplantation: characterization of the antibody target

Two children with Alport's syndrome are described, who developed anti-glomerular basement membrane (GMB) antibody-mediated nephritis after renal transplantation. The reactivity of antibodies in their serum with collagenase-solubilized normal GBM was examined by SDS-PAGE with one- and two-dimensional immunoblotting. The specificity was compared with that of antibodies present in serum from a patient with Goodpasture's syndrome, and a mouse monoclonal antibody (MCA-P1), directed against the Goodpasture antigen. All reacted in a similar way with collagenase-solubilized GBM. Since abnormalities in the composition of the GBM are present in Alport's syndrome, it is proposed that differing antigen composition of GBM in the host compared with the donor kidney, together with transplant rejection, may have provoked the development of post-transplant anti-GBM antibodies.