Potentiation of immune complex injury in rats by pretreatment with subnephrotoxic doses of guinea pig anti-glomerular basement membrane IgG1.

1. Female Wistar rats received a single subnephrotoxic dose of guinea pig anti-glomerular basement membrane (GBM) IgG1, 2.5 mg, followed by infusion of preformed immune complexes (BSA, 5.0 mg/rabbit anti-BSA, 6 mg), 10 X antigen excess. Control groups received guinea-pig IgG1 anti-GBM, or preformed immune complexes alone, or isotonic saline. Systemic reactions were observed clinically during the first 24 h, and 24 h urine was collected for the measurement of proteinuria and hematuria. 2. Blood was collected before and 2 h after the above treatment for the determination of complement (50% hemolytic assay), kininogen (isolated guinea pig assay of released bradykinin-like spasmogenic activity) and activated partial thromboplastin time (APTT). Kidney and lung tissue was examined by light microscopy, immunofluorescence and electron microscopy. 3. Rats treated with guinea pig anti-GBM IgG1 followed by BSA immune complex presented a severe systemic picture, with macroscopic hematuria (9/14), several deaths (8/14), slight proteinuria (24.6 +/- 5.2 mg/day), marked complement consumption (delta = 49.4 +/- 2.4 UCH50/ml), intravascular coagulation and severe diffuse interstitial pneumonia, obliteration of glomerular capillary walls by edema of endothelial cells, without deposition of immune complexes in kidneys or lungs. The control groups showed no signs of systemic reaction (isotonic saline alone) or slight dyspnea (guinea pig anti-GBM IgG1 or immune complexes alone), without proteinuria or macroscopic hematuria, and with foci of interstitial pneumonia. 4. Complement consumption was significant in rats receiving immune complexes alone (delta = 31.1 +/- 1.3 UCH50/ml) and even higher when associated with infusion of guinea pig anti-GBM IgG1 (delta = 49.3 +/- 2.4 UCH50/ml). APTT was significantly lengthened only for the group treated with guinea pig anti-GBM IgG1 plus immune complexes (delta = 18.5 +/- 1.9 s), with no alterations in the other groups. Kininogen consumption was demonstrable for all groups except the saline control and was more extensive in rats which received immune complexes alone or preceded by guinea pig IgG1. 5. These data show that previous infusion of a subnephrotoxic dose of guinea pig IgG1 anti-GBM aggravated the pathological effects of preformed immune complexes by promoting marked complement consumption and activation of the coagulation system, rather than by enhancing tissue deposition.