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DNA AND CELL BIOLOGY
Volume 24, Number 8, 2005
© Mary Ann Liebert, Inc.
Pp. 521–527
Profiles of IgG Antibodies to Nucleocapsid and Spike Proteins
of the SARS-Associated Coronavirus in SARS Patients
YANBIN WANG,
1
ZHAORUI CHANG,
1
JING OUYANG,
1
HAIYAN WEI,
1,2
RENQUAN YANG,
1,3
YANGONG CHAO,
4
JIANGUO QU,
1
JIANWEI WANG,
1
and TAO HUNG
1
ABSTRACT
To evaluate humoral immunity against the SARS-associated coronavirus (SARS-CoV), we studied the pro-
files of IgG antibodies to the nucleocapsid (N) and spike (S) proteins of SARS-CoV. Serum specimens from
10 SARS patients were analyzed by Western blotting and an enzyme-linked immunosorbent assay (ELISA)
using purified recombinant N and truncated S (S1, S2, and S3) proteins as antigens. Western blotting results
demonstrated that 100% of the SARS patients tested positive for N protein-specific antibodies, 50% for S1
protein-specific antibodies, 30% for S2 protein-specific antibodies, and 70% for S3 protein-specific antibod-
ies. The ELISA results, which showed positive rates of IgG reactivity against recombinant proteins N, S1, S2,
and S3, were, respectively, 28.57, 14.29, 14.29, and 14.29% at week 1, 77.78, 55.56, 44.44, and 66.67% at week
2, 100, 75, 75, and 87.5% at week 3, and 100, 77.78, 77.78, and 88.89% after 3 weeks. The average titers of
IgG against recombinant proteins N, S1, S2, and S3 were, respectively, 691, 56, 38, and 84 after 3 weeks. These
results suggest that the recombinant proteins N and S3 are potentially useful antigens for a serological diag-
nosis of SARS. In consideration of possible cross-reactivity among N proteins of SARS-CoV and other coro-
naviruses, immunoassays using recombinant N protein in combination with S3 as antigens might improve the
specificity of SARS diagnoses.
521
INTRODUCTION
C
ORONAVIRUSES ARE LARGE
, enveloped, RNA viruses that
cause respiratory and enteric diseases in humans and ani-
mals. Based on amino acid sequence analysis, known coron-
aviruses have been divided into three groups: groups 1 and 2
infects various mammals and group 3 infects birds. A newly
emerging coronavirus, severe acute respiratory syndrome-asso-
ciated coronavirus (SARS-CoV) was identified as the causative
agent of SARS in 2003 (Drosten et al., 2003; Peiris et al., 2003).
SARS-CoV is not closely related to any of the previously char-
acterized coronaviruses, and does not belong to any of the
known groups of coronaviruses (Marra et al., 2003). The two
previously identified human coronaviruses, HCoV-229E and
HCoV-OC43, cause only mild upper respiratory infections (Lai
and Holmes, 2001). However, SARS-CoV causes severe respi-
ratory infection with a high mortality rate (10%). It is therefore
imperative to understand the differences between SARS-CoV
and other coronaviruses in terms of immune response to ex-
plore the pathogenesis of SARS-CoV as well as to develop ef-
fective diagnostic procedures.
The SARS-CoV genome is 29,727 nucleotides in length and
encodes 23 putative proteins, including four major structural
proteins: nucleocapsid (N), spike (S), membrane (M), and small
envelope (E). S is a large glycoprotein of approximately 150
kDa containing 1255 amino acids (Marra et al., 2003; Rota et
al., 2003). It may mediate membrane fusion and induce neu-
tralizing antibody production (Gallagher and Buchmeier, 2001).
Recent studies indicated that full-length S, expressed by an at-
tenuated vaccinia virus vector, induces binding and neutraliz-
ing antibody production and protects immunized mice from sub-
sequent infection with SARS-CoV (Bisht et al., 2004). N is a
phosphoprotein containing 422 amino acids. The biological
function of the coronavirus N protein is thought to be the bind-
1
National Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, People’s Republic
of China.
2
School of Medicine, Shandong University, Jinan, People’s Republic of China.
3
School of Animal Health Sciences, Nanjing Agricultural University, Nanjing, People’s Republic of China.
4
Beijing Jiuxianqiao Hospital, Tsinghua University, Beijing, People’s Republic of China.
ing of the viral genome to form a helical nucleocapsid that par-
ticipates in viral replication (Baric et al., 1988). It is a major
viral antigen in several known coronaviruses, such as murine
(Liu et al., 2001) and turkey (Wage et al., 1993). Previous stud-
ies with animal coronaviruses have shown that N is abundantly
expressed during infection (Narayanan et al., 2003) and is the
most abundant protein in purified SARS-CoV virions (Rota et
al., 2003). These features imply that S and N proteins are prob-
ably useful in the early diagnosis of SARS.
Today, acute SARS outbreaks have, at least temporarily,
ceased. However, with a wide range of animal reservoirs of the
virus in nature, it is believed that SARS will likely resurface in
the future (Guan et al., 2003; Martina et al., 2003). In the ab-
sence of antiviral drugs or vaccines available against SARS-
CoV, early detection of virus-infected patients is critical for bet-
ter control or prevention of future epidemics. In this paper, we
studied the profiles of IgG antibodies against the S and N pro-
teins by Western blotting and ELISA to evaluate the humoral
immunity features of SARS-CoV and to select ideal antigens
for early diagnosis and/or vaccine development.
MATERIALS AND METHODS
Serum specimens
A total of 50 specimens from 10 patients with SARS were
collected during different stages of illness, including acute and
convalescent sera. These patients fit the World Health Organi-
zation (WHO) definition for probable SARS infection (WHO,
2003)—fever of 38°C or higher, respiratory symptoms (e.g.,
cough, shortness of breath, and difficulty in breathing), hypoxia,
and chest radiograph changes of pneumonia, and history of
close contact with other SARS patients. Serum samples from
healthy donors were collected as negative controls.
Cloning of cDNAs encoding N and truncated S
proteins
Viral RNA was extracted with the TRIZOL
®
Reagent (In-
vitrogen, Carlsbad, CA) from SARS-CoV in a biosafety level
3 laboratory. The SARS-CoV genomic RNA was converted to
cDNA by reverse transcription using random primers (Promega,
Madison, WI). The coding regions for SARS-CoV N and trun-
cated S proteins (S1, S2, and S3) were amplified by PCR us-
ing the resulting cDNA and Pfu polymerase (Stratagene, La
Jolla, CA). The sequence-specific primers were designed ac-
cording to the published cDNA sequences for SARS coron-
avirus strain BJ01 (GenBank accession No. AY278488). The
oligonucleotide primers for nucleocapsid protein were NF: 5-
gaagatcttatgtctgataatggaccccaatc-3and NR: 5-cggaattcttatgc-
ctgagttgaatcag-3. Primers for truncated S [S1 (amino acids
14–403), S2 (amino acids 370–770), S3 (amino acids
738–1196)] were S1F: 5-ggggtaccgaccttgaccggtgcaccac-3and
S1R: 5-cggaattctcatcctggcgctatttgtc-3; S2F: 5-ggggtaccg-
gcgtttctgccactaagttg-3and S2R: 5-cggaattcctagacttgagcgaa-
cacttc-3; S3F: 5-ggggtacccttctccaatatggtagcttttg-3and S3R:
5-cggaattcctattgctcatattttccc-3. The PCR products were then
cloned into the pcDNAII vector (Invitrogen) and confirmed by
DNA sequencing. For the expression of His-tagged proteins,
the open reading frames of these positive clones were cloned
into the pET-30a vector (Novagen) separately.
Protein expression and purification in E. coli
The pET-30a constructs were transformed into E. coli BL21
(DE3) cells (Novagen, Madison, WI), and the expression of re-
combinant proteins was induced by the addition of 0.1 mM iso-
propyl-l-thio-D-galactopyranoside (IPTG) at 37°C for 5 h. The
cells were harvested by centrifugation and the pellet was re-
suspended in binding buffer (20 mM Tris–HCl, pH 7.9, 500
mM NaCl, 5 mM imidazole, 1 mM NaF, and 1 mM PMSF),
sonicated, and centrifuged at 12,000 gat 4°C for 30 min. The
recombinant proteins were analyzed by 15% sodium dodecyl
sulfate–polyacrylamide gel electrophoresis (SDS–PAGE) and
purified using Ni-nitrilotriacetic acid (Ni-NTA) columns ac-
cording to the manufacturer’s instructions (Qiagen, Hilgen,
Germany). The purified protein concentration was determined
using a BCA kit (Pierce, Rockford, IL), aliquoted, and stored
at 80°C until use.
Western blotting
The recombinant SARS-CoV proteins S1, S2, S3, and N were
separated by SDS–PAGE as described above and transferred to
nitrocellulose membranes by electroblotting. The membranes
were blocked with a solution of 5% skim milk and 0.2% Tween
WANG ET AL.
522
FIG. 1. Expression and purification of recombinant N, S1, S2, and S3 proteins in E. coli. (A) Schematic diagram of three over-
lapping fragments within the S protein. (B) SDS-PAGE of the expressed and purified recombinant proteins. Recombinant pro-
teins were expressed in E. coli and purified using an Ni-NTA affinity column (Qiagen) and the purified recombinant proteins
were separated by 15% SDS–PAGE, followed by Coomassie blue staining. Lane M denotes the protein markers.
20 in 50 mM Tris–HCl-buffered saline (TBS, pH 7.4) for 2 h
at room temperature. Sera from convalescent patients with
SARS (used at a dilution of 1:100) and anti-His-antibody (used
at a dilution of 1:1000) (Sigma, St. Louis, MO) were allowed
to react for 2 h at room temperature with the membranes, fol-
lowed by incubation with an alkaline phosphatase-conjugated
secondary antibody (Pierce) according to the manufacturer’s in-
structions. Nitroblue tetrazolium and 5-bromo-4-chloro-3-in-
dolylphosphate (NBT/BCIP; Pierce) was used as the substrate
for membrane color development.
ELISA
Immulon-1 microtiter plates (Nunc, Naperville, IL) were
coated overnight at 4°C with purified recombinant S1, S2, S3,
or N protein (1 mg/ml) diluted in 0.05 M sodium carbonate
buffer (pH 9.6; 100 ng protein/well), and blocked with 1%
bovine serum albumin (BSA) for 2 h at 37°C . After the plates
were washed with TBS containing 0.05% Tween-20 (TBST),
the negative control sera and heat-inactivated sera from SARS
patients, diluted in 0.1% BSA from 1:10 to 1:1280 (100
l/well), were added to each well, and the plates were incu-
bated for 60 min at 37°C. After three washes, 100 l of horse-
radish peroxidase-conjugated goat antihuman IgG (Santa Cruz,
Santa Cruz, CA), diluted 1:5000 in 0.1% BSA, was added to
each well and the plates were incubated for 30 min at 37°C.
The plates were rinsed six times with TBST and 100 l of
3,3,5,5-tetramethylbenzidine (TMB; Sigma) solution was
added to each well and the plates were incubated for 15 min at
37°C . The reaction was stopped by the addition of 50 l of 2
M H
2
SO
4
to each well. Absorbance at 450 nm (A
450
) was mea-
sured using a microplate reader (Model 550, Bio-Rad, Hercules,
CA). The serum samples were examined in duplicate. The cut-
off value was defined as the mean A
450
of control samples plus
two standard deviations (SD).
RESULTS
Expression and purification of recombinant SARS-CoV
N, S1, S2, and S3 proteins in Escherichia coli
To acquire SARS-CoV recombinant proteins, the cDNAs en-
coding SARS-CoV structural proteins N and 3 truncated forms
of the different domains of the S protein (S1, S2, and S3) were
amplified by RT-PCR using total RNA from the lung tissue of
a dead SARS patient. The open reading frames of these posi-
tive clones were inserted into the pET-30a vector and trans-
formed into E. coli BL21 (DE3) cells for His-tagged recombi-
nant protein expression. After purification using a Ni-NTA
affinity column, as described in the Materials and Methods, the
recombinant proteins were examined by 15% SDS–PAGE. As
expected, the N, S1, S2, and S3 recombinant proteins were es-
timated to be approximately 53, 51, 51, and 57 kDa, respec-
tively (Fig. 1). The purities of the four recombinant proteins
were approximately 90%, and all reacted well with the anti-His
antibody (data not shown). These results indicated that the N
and truncated S proteins were expressed correctly and effi-
ciently in E. coli. The recombinant proteins were used as anti-
gens in subsequent studies, including Western blotting and
ELISA.
Reactivity analysis of N and S proteins using sera
from SARS patients
To characterize serological responses during SARS-CoV in-
fection, a Western blotting assay was performed. We tested 50
serum specimens from 10 SARS patients using recombinant
HUMORAL IMMUNITY TO SARS-CoV PROTEINS 523
T
ABLE
1. R
ESULTS FOR
W
ESTERN
B
LOTTING FOR
A
NALYSIS
OF
I
G
G A
NTIBODIES
A
GAINST
SARS-C
O
V N
AND
S P
ROTEINS
IN
S
ERUM
S
PECIMENS FROM
SARS P
ATIENTS
Days after
Patient disease
no. onset NS1 S2 S3
17
9
12
16
18
23
27
12
18
25
39
12
15
17
22
49
13
15
17
22
59
12
16
20
24
67
12
14
17
24
712
14
17
19
25
86
7
9
11
14
97
14
18
20
22
10 7
14
17
19
22
proteins N, S1, S2, and S3 as antigens. After the purified pro-
teins were transferred to nitrocellulose membranes, the im-
munoblot assay was performed as described above. At a 1:100
dilution, all 10 patients tested positive for the N-specific anti-
body, while five tested positive for S1, three for S2, and seven
for S3 (Table 1). As shown in Figure 2, significant crossreac-
tivities were observed between the sera and the recombinant
antigens, although the patterns of reactivity were different
among the three patients. Taken together, these results imply
that: (1) the SARS-CoV N and S proteins are strong antigens
and able to elicit humoral immunity during infection; and (2)
the antigenicities of the recombinant proteins S1, S2, and S3
are different from one another. The antigenicity of the S3 pro-
tein was the highest, whereas that of S2 was the lowest among
the three truncated S proteins. Tests for the presence of IgG an-
tibody against S2 were negative in most cases, even in late clin-
ical stages, but in patient 7 (P7), the S2 protein gave the
strongest antigen signal among the 3 S proteins (Fig. 2). These
results suggest an imbalanced reactivity or immunogenicity be-
tween the different domains of the S protein.
ELISA kinetics of IgG antibodies against SARS-CoV
proteins N, S1, S2, and S3 in sera from SARS patients
To further characterize the immune response to SARS-CoV
N and S proteins and to confirm the conclusions drawn by the
results of the Western blotting assays, paired sera from the 10
SARS patients were also examined by ELISA. Using purified
recombinant SARS-CoV N, S1, S2, and S3 proteins as coated
antigens (1 mg/ml) separately, the 50 serum samples from the
SARS patients and serum samples from healthy donors were
serially diluted in 0.1% BSA from 1:10 to 1:1280 (100 l/well)
and were added to each well to measure the reactivity of the
relevant IgG antibody. The positive rates of IgG reactivity
against the four proteins at different time intervals after SARS
infection were analyzed first. The proportion of patients with
IgG reactivity against N, S1, S2, and S3 were, respectively,
28.57, 14.29, 14.29, and 14.29% at week 1, 77.78, 55.56, 44.44,
and 66.67% at week 2, 100, 75, 75, and 87.5% at week 3, and
100, 77.78, 77.78, and 88.89% after 3 weeks (Fig. 3). These
data demonstrated the stronger immunogenicity or antigenicity
of the N and S3 proteins.
To evaluate the extent of immune responses to the proteins,
the N, S1, S2, or S3 antigen-specific IgG titers from each pa-
tient’s serum at different time points after the onset of illness
were described as shown in Figure 3B–E. The data reveal that
the titers increased with time. The average titers of IgG against
recombinant proteins N, S1, S2, and S3 were, respectively,
3.50 9.92, 1.69 4.04, 1.69 5.24, and 1.87 5.24 at
week 1, 95.92 16.22, 18.82 16.85, 10.56 10.04, and
19.81 14.33 at week 2, 697.92 2.22, 66.44 14.37,
36.23 11.03, and 92.52 8.39 at week 3, and 691.24
2.24, 55.95 11.25, 38.06 10.04, and 84.29 6.56 after 3
weeks (Fig. 4A and B). These data showed that the titer of
antibody against antigen N is much higher than that against
the S proteins, while the titer and positive rates for antibod-
ies against the N and S3 proteins were higher than those
against S1 and S2 during SARS-CoV infection. The results
from the longitudinal dynamics analysis of the IgG antibod-
ies to the recombinant N and S proteins match those of the
Western blotting assay, implying that recombinant N and S3
might be ideal antigens for SARS-CoV antibody detection for
diagnosis.
DISCUSSION
Viral infection elicits neutralizing antibodies in immuno-
competent hosts (Holmes and Enjuanes, 2003). The detection
of antibodies against SARS-CoV has been used to confirm the
diagnosis of SARS. Presently, the most widely used methods
for serodiagnosis of SARS-CoV infection are SARS-CoV-
based ELISA and immunofluorescence assay (IFA), which re-
quire the preparation of viruses as a source of antigen. This re-
quirement may reduce their accessibility for most clinical
laboratories without a biosafety level 3 laboratory facilities
(Ksiazek et al., 2003). The recombinant protein-based ELISA
can be performed in general laboratories without containment
facilities and allows the analysis of the immunogenic viral pro-
WANG ET AL.
524
FIG. 2. Antigenic analysis of recombinant N, S1, S2, and S3 proteins by Western blotting. Partial typical reaction patterns be-
tween the recombinant antigens and the sera from different SARS convalescent patients are shown. The recombinant proteins
were separated by SDS–PAGE and transferred to a nitrocellulose membrane. Each membrane was incubated with serum from a
convalescent patient with SARS (used at a dilution of 1:100) followed by incubation with an alkaline phosphatase-conjugated
secondary antihuman IgG (1:3,000 dilution) antibody. BCIP/NBT was used as the substrate for membrane color development.
(A) Serum collected from patient 7 (P7) at day 25 after the onset of illness. (B) Serum collected from P10 at day 22. (C) Serum
collected from P4 at day 22.
teins of SARS-CoV instead of using the highly infectious
SARS-CoV itself.
In the present work, we expressed N and S proteins in an E.
coli system. Due to the difficulty of expressing full-length S in
E. coli, three overlapping fragments of S protein were ex-
pressed. We then assayed the antibodies against N and the 3
truncated fragments of the S protein in 50 serum samples from
10 SARS-infected patients by Western blotting and ELISA. Our
data suggest that all of the SARS patients were positive for N
protein-specific IgG. The IgG was detectable from day 7 after
the onset of symptoms and was 100% at day 14 by Western
blotting (Table 1). Most of the serum specimens showed in-
creasing antibody titers to the N protein, reaching 1:697.92
2.22 by week 3 (Fig. 4A). The positive rates and average titers
of IgG antibodies against the recombinant truncated S proteins
were lower than that of the N protein (Fig. 4A and B). Inter-
estingly, in three SARS patients (P3, P8, P9), IgG antibodies
against the S protein could not be detected, although they each
HUMORAL IMMUNITY TO SARS-CoV PROTEINS 525
FIG. 3. Variability of positive rates and titers of IgG antibodies to recombinant N, S1, S2, and S3 proteins in sera from SARS
patients. Using purified recombinant SARS-CoV N, S1, S2, and S3 proteins as coated antigens (1 mg/ml), 50 serum samples
from 10 SARS patients at different time points after the onset of illness, and serum samples from healthy people, were diluted
in 0.1% BSA from 1:10 to 1:1280 (100 l/well) and added to each well to assay antibody reactivity against recombinant SARS-
CoV proteins by ELISA. (A) Positive reactivity rates of IgG antibodies to recombinant N, S1, S2, and S3 proteins at different
time points after SARS infection. (B–E) Kinetic of titers of IgG antibodies to recombinant N (B), S1 (C), S2 (D), and S3 (E)
proteins in sera from SARS patients.
had anti-N protein IgG antibodies present (Table 1). One ex-
planation for this may be that the current serological tests were
unable to detect low antibody titers against the S protein and/or
truncated S proteins expressed in an E. coli system lacking the
correct posttranslational modifications, including complex fold-
ing, glycosylation, and oligomerization (Zeng et al., 2004). To
our knowledge, this is the first report on the variability of IgG
titers against the SARS-CoV S protein in SARS patients.
The antigenicity of the S1, S2, and S3 recombinant proteins
were notably different from one another: the antigenicity of the
S3 protein was higher than that of S1 or S2 in Western blotting
assays, and the positive rate and average titer of anti-S3 IgG
were also higher than the others. However, in patient 7, the S2
protein was the strongest antigen of the three truncated S pro-
teins. Five serum IgG samples at different time frames after the
onset of illness all recognized the S2 protein (Table 1) with a
stronger reactivity than against the other S proteins (Fig. 2).
These phenomena may be due to the different immune reactiv-
ities of SARS patients to S and/or the occurrence of noncon-
served amino acid variations that may help the virus evade pres-
sures from host immune responses. Further studies are needed
to understand whether the differences between the immune re-
sponses against the three truncated S proteins are associated with
the pathogenesis of SARS-CoV (Ruan et al., 2003).
Due to the strong antigenicity of the SARS-CoV N protein,
it has been utilized in the serodiagnosis of SARS and studies
on the seroprevalence of nonpneumonic SARS-CoV infections
(Woo et al., 2004a, 2004b). However, very recent studies
showed that the N protein IgG can be detected in some healthy
people (Liu et al., 2004) and antigenic crossreactivities between
the N protein of SARS-CoV and the polyclonal antisera of in-
fectious peritonitis virus (FIPV), porcine transmissible gas-
troenteritis virus (TGEV), and canine coronavirus (CCoV) have
been observed (Sun and Meng, 2004). The antibody against the
SARS-CoV N protein also could be detected in sera from con-
valescent persons infected by HCoV-OC43 or HCoV-229E
(Woo et al., 2004c). It has been reported that antibodies against
human 229E- or OC43-like coronaviruses are widespread in the
human population (McIntosh et al., 1970; Bradburne and Som-
erset, 1972). Therefore, it is possible that false positive cases
could be detected using SARS-CoV N protein, or whole virus,
as an antigen for SARS diagnosis and for identification of the
SASR-CoV animal reservoirs.
The similarity between the amino acid sequences of the
SARS-CoV S protein and other coronaviruses is quite low
(20–27%) (Rota et al., 2003), and SARS-CoV S protein has
specific T cell epitopes and a characteristic antigenicity com-
pared with other coronaviruses (Liu et al., 2003). Thus, the pos-
sibility is slight that SARS-CoV S protein is antigenically cross-
reactive to other known coronaviruses. Although the titer of
IgG antibodies against the S3 protein was much lower than
against the N protein, the positive rate of antibodies against the
S3 protein was similar to that of N, and in most cases, the an-
tibody against S3 was detected earlier than (P5 and P6) or at
least as early as (P2, P4, and P10) that of N (Table 1). Given
such features, the S3 protein may be an ideal antigen for diag-
nostics, and in addition to the N protein, could eliminate the
possible crossreactivity between SARS-CoV and other coron-
aviruses.
In conclusion, our studies suggest that using the recombinant
protein N in combination with recombinant protein S3 as anti-
gens may improve the specificity of SARS diagnosis and may
serve as an effective, safe method for the serological diagnosis
of SARS.
ACKNOWLEDGMENTS
The authors acknowledge Beijing Jiuxianqiao Hospital for
providing the sera of SARS patients. This work was supported
by grants from the SARS Special Project of National High-Tech
R&D Program of China (863 Project; Nos. 2003AA208403 and
2003AA208209), as well as National Nature Science Founda-
tion of China (Nos. 30340025 and 30340026).
REFERENCES
BARIC, R.S., NELSON, G.W., FLEMING, J.O., DEANS, R.J., KECK,
J.G., CASTEEL, N., and STOHLMAN, S.A. (1988). Interactions be-
tween coronavirus nucleocapsid protein and viral RNAs: Implica-
tions for viral transcription. J. Virol. 62, 4280–4287.
BISHT, H., ROBERTS, A., VOGEL, L., BUKREYEV, A., COLLINS,
PL., MURPHY, BR., SUBBARAO, K., and MOSS, B. (2004). Se-
WANG ET AL.
526
FIG. 4. Longitudinal profiles of IgG antibodies to recombi-
nant N, S1, S2, and S3 proteins in SARS patients. (A) Titer of
IgG antibodies to recombinant N; data are shown as the mean
standard deviation. (B) Titers of IgG antibodies to recombinant
S1, S2, and S3 proteins; data are shown as mean value stan-
dard deviation.
A
vere acute respiratory syndrome coronavirus spike protein expressed
by attenuated vaccinia virus protectively immunizes mice. Proc. Natl.
Acad. Sci. USA. 101, 6641–6646.
BRADBURNE, A.F., and SOMERSET, B.A. (1972). Coronative anti-
body tires in sera of healthy adults and experimentally infected vol-
unteers. J. Hyg. (Lond.). 70, 235–244.
DROSTEN, C., GUNTHER, S., PREISER, W., VAN DER WERF, S.,
BRODT, H.R., BECKER, S., RABENAU, H., PANNING, M.,
KOLESNIKOVA, L., FOUCHIER, R.A., et al. (2003). Identifica-
tion of a novel coronavirus in patients with severe acute respiratory
syndrome. N. Engl. J. Med. 348, 1967–1976.
GALLAGHER, T.M., and BUCHMEIER, M.J. (2001). Coronavirus
spike proteins in viral entry and pathogenesis. Virology 279, 371–374.
GUAN, Y., ZHENG, B.J., HE, Y.Q., LIU, X.L., ZHUANG, Z.X., CHE-
UNG, C.L., LUO, S.W., LI, P.H., ZHANG, L.J., GUAN, Y.J., et al.
(2003). Isolation and characterization of viruses related to the SARS
coronavirus from animals in southern China. Science 302, 276–278.
HOLMES, K.V., and ENJUANES, L. (2003). The SARS coronavirus:
A postgenomic era. Science 300, 1377–1378.
KSIAZEK, T.G., ERDMAN, D., GOLDSMITH, C.S., ZAKI, S.R.,
PERET, T., EMERY, S., TONG, S., URBANI, C., COMER, J.A.,
LIM, W., et al. (2003). A novel coronavirus associated with severe
acute respiratory syndrome. N. Engl. J. Med. 348, 1953–1966.
LAI, M.M.C., and HOLMES, K.V. (2001). Coronaviridae: The viruses
and their replication. Fields Virology. (D. Knipe, ed. Lippincott
Williams & Wilkins, Philadelphia, PA) pp. 1163–1185.
LIU, C., KOKUHO, T., KUBOTA, T., WATANABE, S., INUMARU,
S., YOKOMIZO, Y., and ONODERA, T. (2001). DNA mediated im-
munization with encoding the nucleoprotein gene of porcine trans-
missible gastroenteritis virus. Virus Res. 80, 75–82.
LIU, L.D., DONG, S.Z., LI, J.F., and LI, Q.H. (2003). Analysis of struc-
ture basis of immunology characters of SARS coronavirus. J. Chin.
Biotech. 23, 5–11.
LIU, X., SHI, Y., LI, P., LI, L., YI, Y., MA, Q., and CAO, C. (2004).
Profile of antibodies to the nucleocapsid protein of the severe acute
respiratory syndrome (SARS)-associated coronavirus in probable
SARS patients. Clin. Diag. Lab. Immunol. 11, 227–228.
MARRA, M.A., JONES, S.J., ASTELL, C.R., HOLT, R.A., BROOKS-
WILSON, A., BUTTERFIELD, Y.S., KHATTRA, J., ASANO, J.K.,
BARBER, S.A., CHAN, S.Y., et al. (2003). The genome sequence
of the SARS-associated coronavirus. Science 300, 1399–1404.
MARTINA, B.E., HAAGMANS, B.L., KUIKEN, T., FOUCHIER,
R.A., RIMMELZWAAN, G.F., VAN AMERONGEN, G., PEIRIS,
J.S., LIM, W., and OSTERHAUS, A.D. (2003). Virology: SARS
virus infection of cats and ferrets. Nature 425, 915.
MCINTOSH, K., KAPIKIAN, A.Z., TURNER, H.C., HARTLEY,
J.W., PARROTT, R.H., and CHANOCK, R.M. (1970). Seroepide-
miologic studies of coronavirus infection in adults and children. Am.
J. Epidemiol. 91, 585–592.
NARAYANAN, K., CHEN, C.J., MAEDA, J., and MAKINO, S.
(2003). Nucleocapsid independent specific viral RNA packaging via
viral envelope protein and viral RNA signal. J. Virol. 77, 2922–2927.
PEIRIS, J.S., LAI, S.T., POON, L.L., GUAN, Y., YAM, L.Y,, LIM,
W., NICHOLLS, J., YEE, W.K., YAN, W.W., CHEUNG, M.T., et
al. (2003). Coronavirus as a possible cause of severe acute respira-
tory syndrome. Lancet 361, 1319–1325.
ROTA, P.A., OBERSTE, M.S., MONROE, S.S., NIX, W.A., CAM-
PAGNOLI, R., ICENOGLE, J.P., PENARANDA, S., BANKAMP,
B., MAHER, K., CHEN, M.H., et al. (2003). Characterization of a
novel coronavirus associated with severe acute respiratory syndrome,
Science 300, 1394–1399.
RUAN, Y.J., WEI, C.L., EE, A.L., VEGA, V.B., THOREAU, H., SU,
S.T., CHIA, J.M., NG, P., CHIU, K.P., LIM, L., et al. (2003). Com-
parative full length genome sequence analysis of 14 SARS coron-
avirus isolates and common mutations associated with putative ori-
gins of infection. Lancet 361, 1779–1785.
SUN, Z.F., and MENG, X.J. (2004). Antigenic cross-reactivity between
the nucleocapsid protein of severe acute respiratory syndrome
(SARS) coronavirus and polyclonal antisera of antigenic group I an-
imal coronaviruses: Implication for SARS diagnosis. J. Clin. Micro-
biol. 42, 2351–2352.
WEGE, H., SCHLIEPHAKE, A., KORNER, H., FLORY, E., and
WEGE, H. (1993). An immunodominant CD4T cells site on the
nucleocapsid protein of murine coronavirus contributes to protection
against encephalomyelitis. J. Gen. Virol. 74, 1287–1294.
WOO, P.C., LAU, S.K., TSOI, H.W., CHAN, K.H., WONG, B.H.,
CHE, X.Y., TAM, V.K., TAM, S.C., CHENG, V.C., HUNG, I.F., et
al. (2004a). Relative rates of non-pneumonic SARS coronavirus in-
fection and SARS coronavirus pneumonia. Lancet 363, 841–845.
WOO, P.C., LAU, S.K., WONG, B.H., TSOI, H.W., FUNG, A.M.,
CHAN, K.H., TAM, V.K., PEIRIS, J.S., and YUEN, K.Y. (2004b).
Detection of specific antibodies to severe acute respiratory syndrome
(SARS) coronavirus nucleocapsid protein for serodiagnosis of SARS
coronavirus pneumonia. J. Clin. Microbiol. 42, 2306–2309.
WOO, P.C., LAU, S.K., WONG, B.H., CHAN, K.H., HUI, W.T.,
KWAN, G.S., PEIRIS, J.S., COUCH, R.B., and YUEN, K.Y.
(2004c). False-positive results in a recombinant severe acute respi-
ratory syndrome-associated coronavirus (SARS-CoV) nucleocapsid
enzyme-linked immunosorbent assay due to HCoV-OC43 and
HCoV-229E rectified by Western blotting with recombinant SARS-
CoV spike polypeptide. J. Clin. Microbiol. 42, 5885–5888.
WORLD HEALTH ORGANIZATION. (2003). Severe acute respira-
tory syndrome (SARS). Wkly. Epidemiol. Rec. 78, 86–87.
ZENG, F., CHOW, K.Y., HON, C.C., LAW, K.M., YIP, C.W., CHAN,
K.H., PEIRIS, J.S., and LEUNG, F.C. (2004). Characterization of
humoral responses in mice immunized with plasmid DNAs encod-
ing SARS-CoV spike gene fragments. Biochem. Biophys. Res. Com-
mun. 315, 1134–1139.
Address reprint requests to:
Jianwei Wang, M.D., Ph.D.
National Institute for Viral Disease Control and Prevention
Chinese Center for Disease Control and Prevention
100 Ying Xin Jie, Xuan Wu Qu
Beijing 100052, People’s Republic of China
E-mail: wangjw28@vip.sina.com
Received for publication March 23, 2005; accepted April 22,
2005.
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