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J. Exp. Med.,
Volume 188, Number 7, October 5, 1998 1321-1331
By
From the * Department of Medicine, Section of Nephrology, The University of Chicago, Chicago,
Illinois 60637; and the Complement receptor 1-related gene/protein y (Crry) is a potent murine membrane complement regulator that inhibits classical and alternative pathway C3 convertases. In nephrotoxic
serum (NTS) nephritis, injected antibodies (Abs) bind to glomeruli, leading to complement activation and subsequent glomerular injury and albuminuria. To study the phenotypic effects of
continuous complement pathway blockade, transgenic mice were created that express recombinant soluble (rs) Crry directed by the broadly active and heavy metal-inducible metallothionein-I promoter. One transgenic line expressing high levels of rsCrry was propagated. Serum
rsCrry levels were 18.7 ± 2.7 µg/ml (n = 5) at basal level and increased to 118.1 ± 20.6 µg/ml
4 d after addition of zinc to the drinking water. By reverse transcription polymerase chain reaction (RT-PCR), transgene messenger (m)RNA was present in liver, kidney, brain, lung, and
spleen, but not in heart. By in situ RT-PCR analysis of kidneys, transgene mRNA was widely
expressed both in renal glomeruli and tubules. Urinary excretion of rsCrry was 113.4 ± 22.4 µg/ml with a fractional excretion relative to creatinine of 13.2 ± 2.7%, consistent with local
renal production of rsCrry and secretion into urine. The founder and all transgene positive
adult animals have remained healthy with no mortality or apparent phenotypic abnormalities, including infection or immune complex disease. To determine whether rsCrry blocked complement-mediated injury, NTS nephritis was induced by injection of NTS immunoglobulin
(Ig)G, followed by an 18-h urine collection to quantitate the excretion of albumin as a measure of glomerular injury. In transgene-negative littermates (n = 15), transgene-positive animals (n = 10), and transgene-positive animals fed zinc (n = 10), albuminuria was 4,393 ± 948, 1,783 ± 454, and 1,057 ± 277 µg/mg creatinine, respectively (P < 0.01 by ANOVA). Glomerular C3
was evident by immunofluorescence staining in 12/15 transgene-negative animals, but in none
of the transgene-positive animals fed zinc. Thus, we have produced the first transgenic animals
that overexpress a soluble C3 convertase inhibitor. rsCrry expression markedly ameliorates an
Ab-induced disease model in vivo. These results support the hypothesis that continuous complement inhibition at the C3 convertase step is feasible and effective in complement-mediated
injury states.
Department of Medicine, Division of Rheumatology, University of Colorado
Health Sciences Center, Denver, Colorado 80262
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