SUMMARYMice rendered completely deficient of the complement components C3 or C4 were used to determine the influence of complement activation in the heterologous phase of the anti-GBM disease model. In wildtype animals the disease is characterized by a neutrophil infiltrate, capillary thrombosis, proteinuria and C3 and C4 deposited within the glomerulus. The early infiltration of neutrophils into the glomeruli is greater in wild-type mice (2 . 8 Ϯ 0 . 3) compared with C3-deficient (1 . 4 Ϯ 0 . 2) and C4-deficient (1 . 2 Ϯ 0 . 003) mice. Deficiency also protects against the subsequent development of proteinuria (2 . 99 Ϯ 1 . 11 mg/24 h, 0 . 059 mg/24 h and 0 . 327 Ϯ 0 . 14 mg/24 h in wild-type, C3-deficient and C4-deficient mice, respectively) and decreases glomerular capillary thrombosis in both C3-and C4-deficient mice. The degree of protection is greater in the C3-deficient than the C4-deficient animals, suggesting both classical and alternative pathway involvement. These studies support a critical role for complement in the development of anti-GBM disease. However, the protective effect of complement deficiency can be broken if the dose of nephritogenic antibody is increased.

Using thin Plexiglass sections stained with silver, the peritubular capillary area and number of capillary cross-sections can predict both interstitial damage and plasma creatinine concentrations. This technique is both difficult to perform and time-consuming. We have restudied this topic using conventional cryostat sections from 46 biopsies with chronic glomerulonephritis and tubulointerstitial nephritis and two monoclonal antibodies (MoAb) recognising capillary endothelium. Seven pretransplant biopsies acted as controls. The number of capillary cross-sections/mm2 was counted, and the degree of tubular atrophy, interstitial fibrosis and cell infiltration of the interstitium independently assessed on a semiquantitative scale using paraffin sections. These results were correlated with the plasma creatinine or 51Cr-EDTA glomerular filtration rate. Mean number of capillary cross-sections in normal interstitium was 373 +/- 50/mm2, and in the 46 biopsies studied 242 +/- 57/mm2. The number of capillary cross-sections reflected the plasma creatinine (r = 0.82, P less than or equal to 0.0001) and the glomerular filtration rate (r = 0.64, P less than or equal to 0.0001) at the time of biopsy with greater accuracy than any of the conventional gradings of interstitial damage on paraffin sections. We conclude that the use of anti-endothelial cell monoclonal antibodies makes counting capillary cross-sections easy and reliable, and that this technique can be employed to assess the extent of interstitial damage in conventional cryostat sections.

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Persistent fibrin deposition has been observed in kidneys undergoing chronic rejection, and has been suggested to contribute to the obliteration of the vasculature in these grafts. The mechanisms leading to it are not clear. Fibrinolysis, the process to remove fibrin in tissues, is initiated by tissue type plasminogen activator (tPA) and suppressed by type 1 plasminogen activator inhibitor (PAI-1). To investigate their roles in chronic rejection and fibrin deposition, we serially examined the expression of tPA and PAI-1 in an unmodified chronic rejection model, using a Fisher 344 to Lewis rat renal transplant, at 0, 2, 4, 6, 10, 12, 16 and 20 weeks post-transplantation (N = 4 rats/time point in each group). We also analyzed fibrin deposition and the development of chronic changes in the grafts. Our results show that tPA was up-regulated only in the acute phase of rejection (P < 0.05), whereas PAI-1 was induced and persistently expressed during the progressive phase of chronic rejection, together with persistent fibrin deposition in the grafts. Immunohistochemistry showed PAI-1 was mainly localized to the damaged/proliferative vascular intima. The results suggest that persistent induction of PAI-1 may be responsible for the continuance of fibrin deposition, which is associated with irreversible damage and chronic graft loss.