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Immunobiology 209 (2004) 559–568

0171-2985/$ - se

doi:10.1016/j.im

�Correspond

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E-mail addr

www.elsevier.de/imbio

Molecular basis for complement component 6 (C6) deficiency in rats

and mice

Deepak Bhole, Gregory L. Stahl�

Center for Experimental Therapeutics and Reperfusion Injury, Department of Anesthesiology, Perioperative and Pain Medicine,

Brigham & Women’s Hospital, Harvard Medical School, 75 Francis Street, Boston, MA 02115, USA

Received 27 July 2004; accepted 4 August 2004

Summary

Complement component C6 is a part of the lytic membrane attack complex formed during complement activation.Animal modeling to define the role of C5a vs. C5b-9 in human disease has used rodents deficient in C6, yet themolecular basis for the deficiencies has not been ascertained. Oligonucleotides derived from a 493 bp EST sequence ofthe rat C6 gene were used to isolate full-length transcripts of rat C6 mRNA. Sequence analysis confirmed that thederived amino acid sequence for rat C6 is highly homologous to human and mouse. We identified a 31 bp deletion inexon 10 of the C6 gene that leads to C6 deficiency in a strain of PVG rats (PVG/c-) and developed a PCR-basedgenotyping test. In addition, we identified four point mutations in the mouse C6 gene that may result in C6 deficiencyobserved in the Peru-Coppock mouse strain. A serendipitous finding from this study was a coagulation defect in the C6deficient mice and rats. C6 deficient mice or rats demonstrated prolonged tail bleeding times that was reversed bytreatment with purified rat C6 protein. Further, adenosine diphosphate induced platelet aggregation were markedlyreduced in C6 deficient rats. The molecular basis for these coagulations defects is unknown at present.r 2004 Elsevier GmbH. All rights reserved.

Keywords: Cloning; C5b-9; Membrane attack complex

Introduction

The complement system forms an activation cascadeof proteins with similar organization and complexity asthe blood clotting system. Complement may be acti-vated via three distinct pathways; classical, lectin andalternative pathway. Following activation and subse-quent formation of enzymatic complexes called C3 andC5 convertases, the pathways enter a common terminalcytolytic pathway which results in the interaction of five

e front matter r 2004 Elsevier GmbH. All rights reserved.

bio.2004.08.001

ing author. Tel.: +1-617-278-0690; fax: +1-617-730-

ess: gstahl@zeus.bwh.harvard.edu (G.L. Stahl).

complement proteins (i.e., C5b, C6, C7, C8 and C9) toform the membrane attack complex (MAC), C5b-9.

Various animal models and inhibitory studies havedemonstrated the importance of the terminal comple-ment components in models of human disease. Chanceobservations led to the discovery of a strain of PVG rats(PVG/c-) that were deficient in the complement compo-nent C6 and unable to form the C5b-9 complex(Leenaerts et al., 1994; van Dixhoorn et al., 1997). Amutation-prone Peru-Coppock mouse strain deficient incomplement component C6 also is unable to form theC5b-9 complex and apparently does not produce C6protein (Orren et al., 1989). These C6 deficient rodentshave been used extensively to study the role ofcomplement in various disease models (Brandt et al.,

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Table 1. Primers used in this study

WT Rat primers

50 GSP (50-CTCGATGGGCCAGCAACAACAAAGC-30)

30 GSP (50-CCGAGTGCCTCAAACCAGTCGTTCA-30)

C6 50 (50-AAGGCATGACCAGACATCTCAC-30)

C6 30 (50-CACTTTCCTCACTTCCTGTCCG-30)

PVG/c- Rat primers

internal 1 (50-CCTGGAGCGCATGCAATGCTGC-30)

internal 2 (50-AGCCGCCAGGAGCTACAGAACT-30)

internal 3 (50-GAGTGGTTAGAGTCGGTGAAGG-30)

internal 4 (50-TTTCTGGCAGGAGAGCCCAGAG-30)

internal 11 (50-TCCTCGCTGTGGCTCAGGGTTA-30)

internal 12 (50-CTGAGGTGAAATAGTGGGTCCC-30)

Rat C6 genotyping primers0 0

D. Bhole, G.L. Stahl / Immunobiology 209 (2004) 559–568560

1996; Leenaerts et al., 1995; Nakashima et al., 2002;Schmiedt et al., 1998; Tran et al., 2002; Wu et al., 2003;Zhou et al., 2000).

Characterization of the rat C6 deficiency concludedthat the loss of C6 was probably due to a hereditarypoint mutation in the C6 gene or the formation of anunstable transcript (van Dixhoorn et al., 1997). How-ever, the exact nature of the mutation was notdetermined. Identification of the mutation was furtherhampered by the fact that the rat C6 gene was notcloned. Similarly, the molecular characterization of C6deficiency in the mouse has not been characterized. Inthe present study, we have cloned rat C6 gene andidentified the molecular basis for C6 deficiencies in theserat and mouse strains.

C6 mut-1 (5 -GCCAATGTGCTCCATGTCCT-3 )

C6 mut-3 (50-GGTCCCCAGATTATAAATCG-30)

Mouse C6 primers

50 (50-GGACGCTTTGGATGCTCACACA-30)

30 (50-CTCAGGCACAGCTCATGTCCTT-30)

Human C6 cDNA

Mouse C6 cDNA

(Accession #J05064)

393 bpRat EST

(tAccession #AF184900)

Rat C6 cDNA(Accession #AY230250)

1 2 3 4

Start Codon

Stop Codon

1 C6 5’ Primer. Based on conserved human and mouse sequence.

C6 5’ GSP Primer. Based on rat EST sequence.

2 C6 3’ GSP Primer. Based on rat EST sequence.

4 UPM Primer. Clontech Smart RACE kit.

3

Fig. 1. Rat C6 cloning strategy. Rat C6 cDNA was cloned in

two fragments. Primers 2 and 4 were used in a RACE reaction

using the Clontech RACE kit to obtain a �1 kb fragment. The

cDNA template created with the RACE kit was then used as a

template in a PCR reaction using primers 1 and 3 to obtain a

�2.4 kb fragment. The fragments were sequenced to obtain the

complete cDNA sequence. See Table 1 for primer sequences.

Materials and methods

cDNA cloning and sequencing

Rat C6 study

Liver total RNA from PVG/c- or PVG rats wasisolated by TRIzol reagent (Invitrogen Corp, Carlsbad,CA). First strand cDNA was generated using SMARTRACE cDNA kit (BD Bioscience, Palo Alto, CA).Primers utilized for PCR reactions to obtain the wildtype rat C6 cDNA sequence were, UPM 30 RACE (BDBioscience) and the primers listed in Table 1 (WT Ratprimers). Primers utilized for PCR reactions to obtainthe C6 cDNA sequence from PVG/c- rats were the sameas for WT plus additional primers as outlined in Table 1(PVG/c- Rat primers). All PCR reactions (35 cycles)were performed using the Advantage 2 PCR system (BDBioscience) with annealing at 62 1C. All PCR productswere subcloned into PCR-4 TOPO vector (Invitrogen)and sequenced at the Core facility (MBCF, Dana FarberCancer Institute, Boston, MA).

Genomic DNA from rat tails was prepared byproteinase K degradation of tail biopsies. Genotypingwas performed by PCR (35 cycles) using primers listedin Table 1 (Rat C6 genotyping primers) with annealingat 55 1C.

Mouse C6 study

Mouse liver total RNA was prepared as describedabove. First strand cDNA was prepared using ReverseTranscription System (Promega, Madison, WI). PCR

Fig. 2. Nucleotide and amino acid sequence of rat C6. (A) The cDNA sequence of C6 includes the complete coding region,

complete 30 UTR and partial 50 UTR. Deduced amino acid sequence is shown by standard single letter symbols beneath the cDNA

sequence. The numbers on the left indicate the nucleotide bases and amino acid residues (italicized numbers). Peptide fragments in

boxes were confirmed by LC-MS/MS. (B) Comparison of the rat C6 cDNA sequence with the rat genome database (Ratmap)

reveals that the rat C6 gene is comprised of 17 exons and 16 introns spanning 71.7 kb of genomic DNA. The size of introns and

exons are shown in base pairs (bp).

ARTICLE IN PRESSD. Bhole, G.L. Stahl / Immunobiology 209 (2004) 559–568 561

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IntronsIntron 1 = 1531 bpIntron 2 = 1241 bpIntron 3 = 4464 bpIntron 4 = 8914 bpIntron 5 = 14047 bpIntron 6 = 4123 bpIntron 7 = 4246 bpIntron 8 = 7607 bpIntron 9 = 1280 bpIntron 10 = 1561 bpIntron 11 = 312 bpIntron 12 = 3397 bpIntron 13 = 995 bpIntron 14 = 6761 bpIntron 15 = 2288 bpIntron 16 = 6021 bp

ExonsExon 1 = 147 bpExon 2 = 161 bpExon 3 = 144 bpExon 4 = 140 bpExon 5 = 139 bpExon 6 = 203 bpExon 7 = 242 bpExon 8 = 123 bpExon 9 = 165 bpExon 10 = 226 bpExon 11 = 172 bpExon 12 = 112 bpExon 13 = 133 bpExon 14 = 189 bpExon 15 = 91 bpExon 16 = 242 bpExon 17 = 381 bp

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

(B)

Fig. 2. (Continued)

D. Bhole, G.L. Stahl / Immunobiology 209 (2004) 559–568562

was carried out using primers listed in Table 1 (MouseC6 primers).

Purification of rat C6 protein

Rat C6 was purified using a polyclonal immunoaffi-nity column. Rat serum was diluted 1:3 with PBS-EDTA-NaCl buffer (750 mM NaCl, 10 mM EDTA,1�PBS, 0.01% sodium azide, 50 mM benzamidine) andloaded on the column. The column was washed withPBS-EDTA-NaCl buffer. C6 protein was eluted with100 mM glycine (pH 3.0) and 1 ml fractions werecollected. Pooled protein fractions were dialyzed over-night in PBS at 4 1C and subsequently concentrated.Coomassie blue staining of this preparation run on aSDS-PAGE gel showed that the majority of elutedprotein was a single band at the appropriate molecularsize (100 kDa).

Hemolysis assay

Human serum, C6 depleted human serum (AdvancedResearch Technologies) and C6 depleted human serumsupplemented with purified rat C6 were serially diluted1:2 (20% serum to 0.156% serum) in GVB2+ buffer(gelatin veronal–buffered saline: 0.1% gelatin, 141 mMNaCl, 0.5 mM MgCl2, 0.15 mM CaCl2, 1.8 mM sodiumbarbital) and added in duplicate (100 ml/well) to a 96-well plate. The plate was then incubated at roomtemperature for 30 min. Chicken erythrocytes (RBC;5� 107/ml in 4 ml of GVB2+) were sensitized with anti-chicken RBC polyclonal antibody (Intercell Technolo-gies, 0.1% v:v) and incubated at 4 1C for 15 min. TheRBC were washed two times with GVB2+ andresuspended to a final volume of 2.4 ml in GVB2+.

The RBC (30 ml/well, 2.5� 106 cells) were added to theplate containing serum and rat C6, mixed well andincubated at 37 1C for 30 min. The plate was thencentrifuged at 1000g for 2 min, and 85 ml of thesupernatant was transferred to a new 96-well microtiterplate. The plate was read at 415 nm with a microplatereader, and the percent serum complement hemolyticactivity was determined by the following formula (whereOD is optical density): % hemolysis=100� [(ODsample�OD GVB2+ Control)/(OD 100% lysed con-trol�OD GVB2+ Control)], where 100% lysed controlis lysis obtained by addition of 100 ml GVB2+ containing1% Triton to the 30 ml of chicken RBC as preparedabove.

Tail bleeding times

Tail bleeding times were measured as previouslydescribed (Sambrano et al., 2001). Briefly, mice aged6–8 weeks were anesthetized with a mixture of ketamineand xylazine, and tails were transected 2 mm from thetip with a scalpel blade. The bleeding end was immersedin PBS maintained at 37 1C and the time required forstoppage of blood flow (stoppage for 60 s or more) wasrecorded. Assays were terminated at 15 min. Reconstitu-tion of C6 in C6 deficient mice was done by injection of60 mg of purified rat C6 via the penile vein.

Platelet aggregation

Platelet aggregation was performed as we havedescribed previously (Lefer et al., 1988). Briefly, bloodfrom rats was collected in a syringe containing sodiumcitrate (3.9% w/v, 9:1 v/v) and centrifuged at 200g for15 min. The top layer, platelet rich plasma (PRP), was

ARTICLE IN PRESSD. Bhole, G.L. Stahl / Immunobiology 209 (2004) 559–568 563

removed and the remaining sample was centrifuged at2000g for 20 min to obtain the platelet poor plasma(PPP). Platelet counts in PRP were adjusted to2� 108 cells/ml with PPP. Platelet aggregation wasmonitored using a turbidimetric aggregometer (Chron-olog Corp, Haverton, PA) with samples stirred con-stantly at 1000 rpm and 37 1C. Platelet aggregation wasinduced using ADP (Chronolog Corp, Haverton, PA).

Statistical methods

Data are represented as mean7SEM. Statisticalcomparisons of groups were made with one-wayANOVAs followed by posthoc analysis. Differenceswere considered statistically significant at a value ofpp0.05.

Results

Cloning of rat C6 cDNA

The rat C6 cDNA was cloned based on the homologybetween human and mouse C6 genes. BLAST searches

Fig. 3. Alignment of C6 amino acid sequences from human, mouse

mouse and rat indicates C6 amino acid sequences are highly conser

84% and 90% similar to human and mouse sequences, respectively

of Genbank using human and mouse C6 cDNAsequences identified a 393 bp expressed sequence tag(EST), UI-R-C1-kk-a-08-0-UI, from the University ofIowa rat EST project. Two gene specific oligonucleo-tides, 50 GSP and 30 GSP, were designed based on theEST sequence. RT-PCR reactions utilizing rat 30 GSPprimer, Clontech UPM 30 RACE primer, rat 50 GSPprimer and rat C6 50 primer (designed from conservedhuman and mouse C6 sequences) generated partiallyoverlapping 2.4 and 1.0 kb fragments, respectively(Fig. 1). The rat C6 cDNA sequence was assembledfrom the partially overlapping sequences of the twofragments. Full length rat C6 cDNA was then obtainedusing the rat C6 50 primer and the rat C6 30 primer(designed based on the sequence of the 1.0 kb fragment).

Nucleotide sequence of rat C6

The complete coding region of the rat cDNA iscontained within our full-length cDNA transcript of2805 nucleotides (Accession ]AY230250, Fig. 2A),which includes the previously described 492 bp cDNAfragment (Van Dixhoorn et al., 1997). The complete 30

untranslated region, which was obtained by 30 RACE,

and rat. Alignment of C6 amino acid sequences from human,

ved in human, mouse and rat. Rat C6 amino acid sequence is

.

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115

135

0% 1% 2% 3% 4% 5% 6% 7% 8% 9% 10% 11%

% Human Serum

% H

emo

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Normal HS C6 depleted HS

C6 depleted HS+Rat C6

After Before MW(kDa)−203

−118−86

−51.6

−34.1

−19.2

(A)

(B)

Fig. 4. Purification of functional rat C6 protein. (A) C6

protein was isolated from normal rat serum by affinity

chromatography and run on a 10% SDS-PAGE gel. ‘‘After’’

lane is purified rat C6 following removal of contaminating Ig

present in the ‘‘Before’’ lane. (B) Purified rat C6 was added to

C6 deficient human serum (HS) at physiological concentration

(final concentration of 60mg/ml in 100% C6 deficient HS).

Addition of purified rat C6 protein restored the CH50 activity

to a level observed in normal human serum. Symbols represent

the means of 3 experiments done in duplicate.

D. Bhole, G.L. Stahl / Immunobiology 209 (2004) 559–568564

extends for 201 bp after the stop codon. We were unableto obtain a distinct product using 50 RACE andtherefore were only able to amplify a part of the 50

untranslated region utilizing a consensus primer basedon the 50 untranslated region from the human andmouse C6 sequence. BLAST search of the rat genomeproject (RATMAP) using a fragment of the cDNAsequence, identified a genomic contig from chromosome2 which contained the entire genomic rat C6 sequence.Alignment of the cDNA sequence with the genomicsequence allowed us to identify the exon–intronboundaries. The rat C6 gene (Accession ]AY343914) iscomposed of 17 exons and 16 introns spanning �71.7 kbof genomic DNA (Fig. 2B). The exons range from 91 to381 bp in length, whereas the introns range from 312 to14047 bp in length. The cytogenetic location of the geneis 2q16.

Derived amino acid sequence of rat C6

The predicted amino acid sequence of rat C6 is highlyhomologous to the amino acid sequences of human andmouse C6 (Fig. 3). As expected for a secreted protein,the first 21 residues in the amino acid sequence have thetypical features of a signal peptide, a 13-residue stretchof mainly hydrophobic residues flanked by positivelycharged residues on either side, which is most likelycleaved after the alanine residue. The mature peptideafter cleavage of the signal sequence is composed of 913residues with a calculated molecular mass of 102 kDabefore any modifications. We purified rat C6 with anapparent molecular mass of approximately 80 kDaunder non-reduced conditions (118 kDa under reducedconditions; data not shown) by affinity chromatographyusing polyclonal antibody against human C6. This bandwas excised and sent for micro-sequencing by liquidchromatography tandem mass spectrometry (LC-MS/MS), which confirmed four regions of the derived aminoacid sequence (see Fig. 2A), and has a high degree ofhomology with human (84%) and mouse (90%)complement C6. After removal of contaminating ratIgGs (upper band in the ‘‘before’’ lane in Fig. 4A), weused the purified rat C6 (only band present in the‘‘after’’ lane in Fig. 4A) in a hemolytic assay using C6deficient human sera and sensitized chicken RBCs.Supplementation of C6 deficient human sera with theappropriate amount of rat C6 (i.e., 10% normal humansera contains 6 mg C6/ml) restored hemolytic activity(Fig. 4B).

Identification of mutation leading to C6 deficiency in

PVG/c- rats

A chance observation that a strain of PVG rats lackedCH50 activity led to the discovery of C6 deficient PVG/

c- rats (Leenaerts et al., 1994). It was postulated thatthese rats may carry a hereditary mutation which leadsto the loss of C6 protein and an approximately 100-folddecrease in C6 transcript levels (van Dixhoorn et al.,1997), but the exact nature of the mutation wasunknown. Quantitative real time RT-PCR demon-strated that the level of liver C6 transcript in C6deficient rats was reduced by 150-fold compared to wild

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Fig. 5. Exon 10 from C6 sufficient and C6 deficient rats. (A) Comparison of the exon 10 sequence from C6 sufficient (C6_SUF) and

C6 deficients (C6_DEF) rats revealed a 31 nucleotide deletion in C6 deficient rats. (B) PCR amplification of exon 10 from genomic

tail DNA of C6 sufficient and deficient rats.

D. Bhole, G.L. Stahl / Immunobiology 209 (2004) 559–568 565

type PVG rats (data not shown). Due to the extremelylow levels of C6 transcript we were unable to amplify thefull-length mutant C6 transcript from the PVG/c- ratsby RT-PCR. Therefore, five sets of internal primers (seeTable 1) were designed to obtain five partially over-lapping RT-PCR products, which were sequenced andassembled to obtain the complete C6 cDNA sequencefrom PVG/c- rats (Fig. 1). Alignment of the PVG/c- andPVG C6 cDNA sequences identified a 31 bp deletion inexon 10 in C6 PVG/c- cDNA (Fig. 5A). This deletionleads to a frame shift in the reading frame and causespremature termination of translation 194 bp down-stream of the deletion. Primers (Table 1) flanking the31 bp deletion site were designed to verify the deletion andprovide a rapid PCR test for genotyping PVG/c- rats usinggenomic DNA isolated from tails. As expected, the PCRproduct obtained using these primers is smaller fromPVG/c- rats compared to PVG rats (Fig. 5B).

Identification of mutations leading to C6 deficiency

in a strain of C3H/He mice

C6 deficient mice were derived from a Peruvian strainbackcrossed with C3H/He mice for 10 generations(Orren et al., 1989). These mice lack functional C6 andantigenic activity but the molecular basis of thedeficiency is unknown. A set of primers was designedbased on the mouse C6 cDNA sequence from Balb/cmice (Genbank NM_016704) to amplify full lengthcDNA from wild type C3H/He and C6 deficient mice byRT-PCR. The RT-PCR products were �2.2 kb in length

and of equal intensity indicating that there is noreduction in the level of C6 transcript in the deficientmice unlike that observed in the PVG/c- rats (data notshown and confirmed by quantitative real time RT-PCR). Alignment of the cDNA sequences from wildtype C3H/He and C6 deficient mice identified sevenindividual bp point mutations in C6 deficient mice(Fig. 6A). Four of these point mutations yield aminoacid substitutions, which may result in C6 deficiency(Fig. 6B).

C6 deficiency affects coagulation in rats and mice

A serendipitous finding from these studies was acoagulation defect in C6 deficient rats and mice. Whileobtaining tail samples for our genomic studies weobserved that the deficient animals tended to haveprolonged bleeding compared to their wild type counter-parts. Our PRP study from C6 deficient rats revealedthat ADP induced platelet aggregation is markedlyreduced in PVG/c- rats compared to wild type PVG rats(Fig. 7A). There was no detectable difference inmaximum aggregation of platelets from PVG andPVG/c- rats upon stimulation with 10 mM ADP;however, stimulation with 5 or 2 mM ADP exhibited asignificant reduction in maximum aggregation. Plateletsfrom wild type PVG rats treated with an inhibitory anti-C5 monoclonal antibody (18A; 100 mg/ml) (Vakevaet al., 1998) reveal a similar significant reduction inmaximal aggregation compared to untreated platelets(Fig. 7B). However, treatment of human PRP with

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C6 SUF GGG AGA TCA AGG ACG TAC GGTC6 DEF GTG AAA TCG ATG ACT TAT GAT

Gly Arg Ser Arg Thr Tyr Gly

Val Lys Met Asp

(A)

(B)

Fig. 6. Point mutations in C6 deficient mice. (A) C6 cDNA was cloned from C6 deficient and C6 sufficient mice (C3H/He

background) and sequenced. The cDNA sequences were aligned with the C6 cDNA sequences from FVB and BALB/c mice from

Genbank. The alignment demonstrates that C6 deficient mice have seven point mutations in the C6 gene that may induce C6

deficiency. (B) Analysis of codons affected by the point mutations reveals that four out of seven point mutations yield amino acid

substitutions in C6 deficient mice.

D. Bhole, G.L. Stahl / Immunobiology 209 (2004) 559–568566

anti-C5 monoclonal antibody (5G1.1; 20 mg/ml) had noeffect on ADP induced aggregation (Fig. 7C).

We also assessed the effect of C6 deficiency on tailbleeding time in C6 deficient mice. C6 deficient mice hadprolonged bleeding times compared to wild type C3H/He mice (po0.05; Fig. 7D). The prolonged bleedingtime observed in C6 deficient mice was reversed bypretreatment with purified rat C6 (7 mg/g body weight)(po0.05 compared to C6 deficient).

Discussion

The C6 gene in the present study encodes the secondcomponent of the rat terminal complement activationroute that has been cloned and completely sequenced.The first terminal activation pathway component of therat complement system characterized was C9 (Accession]U52948). Rat C5, C7 and C8 genes remain to becloned; however, partial sequences of C5 (C5a) and C7

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C3H Wild Type (n=7) C6 Def (n=8) C6 Def + Rat C6 (180ug) (n=6)

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(A)

(C) (D)

(B)

Fig. 7. C6 deficiency affects blood coagulation. (A) Platelet aggregation in PRP from C6 deficient (Def) and C6 sufficient (Suf) rats.

(B) Platelet aggregation in PRP from C6 Suf rats pretreated with 100mg/ml of anti-rat C5 (18A) inhibitory monoclonal antibody or

PBS. (C) Platelet aggregation in human PRP pretreated with anti-human C5 monoclonal antibody (5G1.1, 20 mg/ml) and human

PRP pretreated with PBS. There was no difference in platelet aggregation in human PRP pretreated with anti-human C5. (D)

Measurement of bleeding times in C3H Wild type mice, C6 Def mice and C6 Def mice treated with rat C6 (180 mg). *po0.05 vs. C3H

Wild Type or C6 Def+rat C6.

D. Bhole, G.L. Stahl / Immunobiology 209 (2004) 559–568 567

are already present within Genbank. In addition, therecent completion of the rat genome project (RatGenome Sequencing Project Consortium, 2004) simpli-fies the identification of the genomic structure of thesegenes. Availability of the complete sequences of allcomponents of rat MAC will facilitate expression ofrecombinant proteins allowing the development of novelinhibitory monoclonal antibodies against these proteinsand the study of structure and function interactionsbetween the C5b-9 components.

The discovery of PVG/c- rats, which are deficient inC6, has proven to be extremely important as this is theonly inbred complement deficient rat currently availablefor investigators to study the role of complement invarious disease models. A previous study undertaken tocharacterize this deficiency concluded that the PVG/c-rats showed an approximate 100-fold reduction in thelevel of C6 transcript and that the size of the C6 mRNA(e.g., northern blot) from PVG/c- rats was identical tothe C6 mRNA from control PVG rats (Van Dixhoorn etal., 1997). In this study, we have identified a small 31 bpdeletion in exon 10 of the C6 gene from PVG/c- rats,which leads to disruption of the open reading frame andconfirmed a 150-fold reduction in C6 mRNA levelsusing quantitative real time RT-PCR. It is possible thatthe deletion leads to formation of an unstable mRNA,which in combination with production of a truncatedpeptide that is likely rapidly degraded, induces C6deficiency. We have also developed a simple PCR testfor genotyping PVG/c- rats using tail DNA that will

allow the backcrossing of this deficiency onto othergenetic backgrounds. Further, use of C6 deficientanimals in conjunction with the inhibition of C5 witha monoclonal anti-rat C5 monoclonal antibody (Vakevaet al., 1998) will allow careful investigation of the role ofC5a vs. C5b-9 complex in a variety of disease models.The added ease of production of native or recombi-nant rat C6 will also allow restoration of the C5b-9pathway to confirm the roles of C5a and C5b-9 indisease models.

A C3H/He C6 deficient mouse strain was establishedmore than a decade ago (Orren et al., 1989). We haveidentified seven point mutations in the C6 gene fromthese animals, four of which lead to amino acidsubstitutions possibly disrupting the tertiary structureof the protein causing the deficiency. It is also probablethat, the amino acid substitutions interfere with thebinding of C6 with either C5b or C7 thus inhibiting theformation of C5b-9. We are currently developing a SNPtest for genotyping the C6 deficient mice in order to beable to cross the deficiency onto other genetic back-grounds. The use of anti-mouse C5 monoclonal anti-body (Zhao et al., 2002; Zhou et al., 2000) can be usedalong with the C6 deficient mice to delineate the role ofC5a vs. C5b-9 in disease models. The combined use ofthese C6 deficient rodents in similar models of humandisease and the inhibition of C5a with either monoclonalantibody or a peptide C5a receptor antagonist (Finch etal., 1999) will allow dissection of the roles of C5a vs.C5b-9 in two different species.

ARTICLE IN PRESSD. Bhole, G.L. Stahl / Immunobiology 209 (2004) 559–568568

We have also shown that the C6 deficiency in rats ormice leads to a defect in coagulation. PRP from C6deficient rats revealed decreased platelet aggregationupon stimulation with ADP. Treatment of WT PRPwith inhibitory anti-rat C5 antibody also induced asimilar significant reduction in platelet aggregation.Furthermore, C6 deficient mice exhibited increased tailbleeding times that could be reversed by restoration withpurified rat C6 protein. These data suggest a role for theMAC or a C5b-6 complex in coagulation. These studiesare similar in scope to observations revealed in alteredplatelet aggregation studies in C6 deficient rabbits(Christian and Gordon, 1975) and humans (Wautier etal., 1979). This would not be surprising since multiplecomponents of the coagulation and complement cas-cades interact with each other. However, our resultsindicate that inhibition of C5 does not alter aggregationof human PRP. Hence, it is possible that the dependenceof platelet aggregation on terminal complement compo-nents might be limited to rodents.

In summary, we have cloned and sequenced the rat C6gene. Identification of the molecular basis of the C6deficiencies observed in rats and mice may aid in thedevelopment of novel tools for the study of the C5b-9complex in models of disease. We observed alteredbleeding profiles in these C6 deficient strains, however,the molecular basis for this phenotypic effect, remains tobe elucidated.

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