Mapping of a gene for the Mr 48,000 tubular basement membrane antigen in the rat

Molecular characterization of a major nephritogenic domain in the autoantigen of anti-tubular basement membrane disease

Anti-tubular basement membrane (alpha TBM) disease is a form of primary interstitial nephritis mediated by autoimmune T cells and alpha TBM antibodies. In mice and humans the nephritogenic immune response is directed to a glycoprotein (3M-1) found along the proximal tubule of the kidney. We have isolated cDNAs from an expression library that encodes for the common framework domain of the 3M-1 antigen. This common domain was once related evolutionarily to a family of intermediate filament-associated proteins. Northern hybridization revealed that all isoforms of 3M-1 range between 1700 and 1900 base pairs and in situ hybridization studies indicate that transcripts are found in tubular epithelium. Candidate peptide fragments were deduced and synthesized from the sequence encoding this common framework domain, and one of the peptide residues was able to bind a monoclonal 3M-1-reactive alpha TBM antibody, stimulate the growth of 3M-1-reactive helper T cells, and induce nephritogenic effector T cells capable of producing interstitial nephritis. Our results indicate that a unique, immunodominant region of the 3M-1 antigen is an informative participant in the emergence of autoimmune injury to certain basement membranes.

A spontaneous hybridoma producing autoanti-idiotypic antibodies that recognize a V kappa-associated idiotope in mercury-induced autoimmunity

Anti-idiotypic (Id) antibodies have been suggested to play a role in the self regulation process observed in Brown-Norway rats developing mercury-induced autoimmunity. However, the presence of such antibodies has not yet been directly demonstrated. For that purpose, spleen cells from a mercury-injected rat were fused and the resulting hybridomas tested for their anti-Id activity against monoclonal anti-glomerular basement membrane (GBM) antibodies produced in this model. A monoclonal antibody (mAb) was obtained that specifically reacted in an enzyme-linked immunosorbent assay with an anti-GBM mAb and to a much lesser extent with another one produced in the same fusion. In Western blot experiments this autoanti-Id mAb reacted under reducing conditions with the kappa L chains but not with the H chains of the two anti-GBM mAb. It did not react with the kappa L chains of eight other rat mAb. This mAb is therefore an autoanti-Id mAb that recognizes a V kappa-associated Id expressed on two anti-GBM mAb. These results demonstrate that anti-GBM antibodies and their corresponding autoanti-Id antibodies are simultaneously produced during this disease. Whether or not these autoanti-Id antibodies have a regulatory and/or a pathogenic role in this disease remains to be established.

Specificity and cross-reactive idiotypes of anti-glomerular basement membrane autoantibodies in HgCl2-induced autoimmune glomerulonephritis

Mercury-induced autoimmune glomerulonephritis in the Brown-Norway (BN) rat is characterized by the successive appearance of linear and granular glomerular IgG deposits. Anti-laminin autoantibodies represent the major part of the anti-glomerular basement membrane (GBM) antibodies produced in this model. Fusions were performed in this model and four anti-GBM monoclonal antibodies (mAb) were obtained. Three of them were laminin specific. Using rabbit anti-idiotype antibodies, cross-reactive idiotypes (CRId) were characterized on anti-laminin antibodies. They were expressed on the three anti-laminin mAb, on kidney-eluted and circulating anti-laminin antibodies. CRId-bearing immunoglobulins were detected transiently in the circulation and paralleled the anti-laminin antibody activity. By immunofluorescence studies on kidney cryostat sections two different CRId were defined. One was localized close to the antigen-combining site since it was not revealed on kidney-bound antibodies, in contrast with the second CRId. This latter CRId was also found deposited in a typical linear pattern in the early phase of the disease and in a granular pattern in the late phase, demonstrating that these CRId are components of immune deposits. Taken together, these results suggest that in this model of T-dependent polyclonal B cell activation, restricted sets of V genes encode for at least a part of the anti-GBM autoantibodies.