Transplantation of renal allografts into recipients with circulating anti-HLA antibodies results in hyperacute rejection. In some cases, however, antibodies return without causing harm; this phenomenon has been termed 'accommodation'. We have investigated this process in human allotransplantation. We removed anti-HLA antibodies by immunoadsorption in seven highly sensitized dialysis patients who subsequently underwent renal transplantation. Immunohistochemistry of renal biopsies for IgG and antiapoptotic proteins was performed. We also developed a model of 'accommodation' using anti-HLA antibodies eluted from sensitized patients and incubated with human umbilical vein endothelial cells (HUVECs) at different concentrations. Their effect on HUVEC phenotype was then analysed. Anti-donor antibody returned in 4/7 patients, without evidence of hyperacute rejection. Three out of four of these 'accommodated' grafts showed specific endothelial up-regulation of Bcl-xL and 2/2 tested positive for endothelial IgG deposition. HUVECs incubated with subsaturating concentrations of anti-HLA antibody showed increased expression of Bcl-xL, were rendered refractory to endothelial cell activation and became resistant to complement-mediated lysis. In contrast, HUVECs incubated with saturating concentrations underwent activation and expressed low levels of Bcl-xL. In conclusion, endothelial Bcl-xL expression defines the accommodation process in human allografts and this phenotype may be initiated by exposure of endothelium to low concentrations of anti-donor HLA antibodies.

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ANCA with specificity for proteinase 3 (PR3), a neutrophil primary granule enzyme, are of diagnostic value in Wegener's granulomatosis (WG) and certain other forms of systemic vasculitis. There is evidence to suggest that they play a pathogenic role in disease, and that the interaction of ANCA with PR3 is likely to be important. We showed, using a resonant mirror biosensor, that C-ANCA from different patients recognized the same or closely related epitopes on PR3. Studies using linear peptides in the SPOT system confirmed the highly restricted nature of this interaction and identified five linear epitopes. Fluid-phase inhibition studies, using a different set of peptides, validated the sequences involved. Using a computer-generated model of the structure of PR3, four of five epitopes were shown to be intimately linked with the catalytic site. The restricted number of epitopes, and their location at the catalytic site, has important implications for the role of C-ANCA in the pathogenesis of vasculitis.

In order to study disease mechanisms and potential forms of therapy in glomerulonephritis, a model of experimental autoimmune glomerulonephritis (EAG) has been developed in the rat. We have examined the response of Brown-Norway (BN) rats to a single i.m. injection of collagenase-solubilised homologous (Sprague-Dawley, SD) or isologous (BN) glomerular basement membrane (GBM), with and without complete Freund's adjuvant (CFA). There was a dose-dependent circulating anti-GBM antibody response to all preparations of rat GBM. Animals given either antigen alone at a dose of 2 mg/kg developed circulating anti-GBM antibodies, which reached peak values by 6 weeks (63 +/- 5% following SD GBM; 53 +/- 8% following BN GBM), but did not develop glomerular deposits of IgG or nephritis. Animals given 2 mg/kg SD GBM in CFA developed greater concentrations of anti-GBM antibody by 6 weeks (122 +/- 20%) together with linear deposits of IgG on glomerular and tubular basement membranes (TBM), albuminuria (mean 7 mg/24 h), and variable focal segmental necrotising glomerulonephritis with mild interstitial nephritis. The same dose of BN GBM in CFA produced similar concentrations of circulating antibody (144 +/- 26%), with linear deposits of IgG on GBM but rarely TBM, little albuminuria, and variable mild focal glomerulonephritis. Other strains injected with SD GBM in CFA showed a variable circulating anti-GBM antibody response, which was similar to that of BN rats in PVG and DA rats but lower in LEW and WAG rats. Linear deposits of IgG on the GBM were detected in a proportion of PVG and DA rats, but not in LEW or WAG rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental autoimmune glomerulonephritis (EAG), an animal model of Goodpasture’s disease, can be induced in Wistar-Kyoto (WKY) rats (RT1-l) by immunization with rat glomerular basement membrane (GBM) in adjuvant. The model in this rat strain is characterized by anti-GBM antibody production accompanied by focal necrotizing glomerulonephritis with crescent formation. The main autoantigen in humans and rats has been identified as the non-collagenous domain of the α3 chain of type IV collagen (α3(IV)NC1). By contrast, Lewis (LEW) rats with the same MHC background (RT1-l), immunized with the same antigen, develop similar levels of circulating anti-GBM antibodies, but no histological evidence of nephritis. In order to investigate the genetic basis of susceptibility to EAG, we examined the response of both F1 (WKY × LEW) and backcross (BC1; WKY × F1) rats to immunization with rat GBM. F1 animals were completely resistant to the development of EAG, while BC1 animals showed a range of responses from severe crescentic glomerulonephritis to no histological evidence of disease. The results indicate that EAG is inherited as a complex trait under the control of WKY genes unlinked to the MHC. cDNA sequence analysis of α3(IV)NC1 in the two parental strains was identical, indicating no predicted amino acid sequence variation in the α3(IV)NC1 domain between these strains. Radiation hybrid mapping, using two separate PCR amplicons from rat α3(IV)NC1, localized rat Col4a3 to a region of chromosome 9. Since Col4a3 (encoding the autoantigen) is a candidate for susceptibility to EAG, we screened the region of rat chromosome 9 where Col4a3 is localized, using polymorphic microsatellite markers in segregating BC1 progeny. No significant linkage was detected. These results exclude Col4a3 as a recessive susceptibility gene for EAG in the BC1 progeny.