1321 J. Exp. Med.  The R ockefeller University Press • 0022-1007/ 98/ 10/ 1321/ 11 $2.00 Volume 188, Number 7, October 5, 1998 1321–1331 http:/ / www.jem.org Transgenic Mice Overexpressing the Complement Inhibitor Crry as a Soluble Protein Are Protected from Antibody-induced Glomerular Injury By R ichard J. Q uigg,* Chun He,* Alice Lim,* Dawn Berthiaume, ‡ Jessy J. Alexander,* Damian Kraus, ‡ and V. Michael Holers ‡ From the *Department of Medicine, Section of N ephrology, T he University of Chicago, Chicago, Illinois 60637; and the ‡ Department of Medicine, Division of R heumatology, University of Colorado Health Sciences Center, Denver, Colorado 80262 Summary Complement receptor 1–related gene/ protein y (Crry) is a potent murine membrane comple- ment regulator that inhibits classical and alternative pathway C3 convertases. In nephrotoxic serum (NTS) nephritis, injected antibodies (Abs) bind to glomeruli, leading to complement ac- tivation and subsequent glomerular injury and albuminuria. To study the phenotypic effects of continuous complement pathway blockade, transgenic mice were created that express recom- binant soluble (rs) Crry directed by the broadly active and heavy metal-inducible metallothio- nein-I promoter. One transgenic line expressing high levels of rsCrry was propagated. Serum rsCrry levels were 18.7  2.7 g/ ml ( n = 5) at basal level and increased to 118.1  20.6 g/ ml 4 d after addition of zinc to the drinking water. By reverse transcription polymerase chain reac- tion (R T-PCR ), transgene messenger (m)R NA 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 g/ 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 comple- ment-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 g/ 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 com- plement inhibition at the C3 convertase step is feasible and effective in complement-mediated injury states. Key words: Crry • mice, transgenic • anti-glomerular basement membrane disease • complement inactivators • complement A ctivation of the complement pathway occurs after the binding of Ab to local tissue Ags. Products of comple- ment activation can lead to varied inflammatory events, such as recruitment and activation of leukocytes by C3 and C5 cleavage fragments, as well as a number of cellular events mediated by C5b-9 (for reviews see references 1, 2). Using several experimental approaches, the complement system has been shown to play an important role in im- mune complex disease models. In early studies, this was done through systemic depletion of complement with co- bra venom factor (3). More recently, an mAb that blocks the cleavage of C5, as well as neutralizing polyclonal Ab to C5a, has been used successfully (4–6). R odents that are congenitally deficient in a single component such as C5 or C6, or that have been made deficient in a single compo- nent by homologous recombination, such as C3 or C4 (7), have also been studied. In these animals with complement deficiencies, complement activation is blocked distal to the on March 2, 2016 jem.rupress.org Downloaded from Published October 5, 1998