Kinetics of Severe Acute Respiratory Syndrome (SARS) Coronavirus-Specific Antibodies in 271 Laboratory-Confirmed Cases of SARS

The sensitivities and specificities of an immunofluorescence assay and an enzyme immunoassay for detection of antibodies specific for severe acute respiratory syndrome coronavirus (SARS-CoV) were compared for 148 laboratory-confirmed SARS cases. The appearance and persistence of SARS-CoV-specific antibodies were assessed, with immunoglobulin G detected in 59% of samples collected within 14 days and persisting for 60 to 95 days after the onset of illness.     

Profile of Antibodies to the Nucleocapsid Protein of the Severe Acute Respiratory Syndrome (SARS)-Associated Coronavirus in Probable SARS Patients

Profiles of antibodies to the nucleocapsid protein of the severe acute respiratory syndrome (SARS)-associated coronavirus in 445 probable SARS patients and 3,749 healthy people or non-SARS patients were analyzed by antigen-capturing enzyme-linked immunosorbent assay. Antinucleocapsid antibodies were elucidated in 17.5% of the probable SARS patients 1 to 7 days after the onset of symptoms and in 80% of the patients 8 to 14 days after the onset. About 90% of the probable SARS patients were positive 15 or more days after illness. Antibody titers increased up to 70 days, and high antibody titers were maintained at least for another 3 months. Of the healthy people and non-SARS patients, only seven (0.187%) were weakly positive.     

Profile of antibodies to the nucleocapsid protein of the severe acute respiratory syndrome (SARS)-associated coronavirus in probable SARS patients

Profiles of antibodies to the nucleocapsid protein of the severe acute respiratory syndrome (SARS)-associated coronavirus in 445 probable SARS patients and 3,749 healthy people or non-SARS patients were analyzed by antigen-capturing enzyme-linked immunosorbent assay. Antinucleocapsid antibodies were elucidated in 17.5% of the probable SARS patients 1 to 7 days after the onset of symptoms and in 80% of the patients 8 to 14 days after the onset. About 90% of the probable SARS patients were positive 15 or more days after illness. Antibody titers increased up to 70 days, and high antibody titers were maintained at least for another 3 months. Of the healthy people and non-SARS patients, only seven (0.187%) were weakly positive.     

Antibody responses against SARS-coronavirus and its nucleocaspid in SARS patients.

BACKGROUND: SARS-Cov is the etiologic agent of severe acute respiratory syndrome. An understanding of the antibody responses to the viral components is very important for diagnosis and vaccine development. OBJECTIVE: The spectrum of SARS-specific antibody profiles in SARS patients was investigated from 7 to 210 days after the onset of the symptoms. STUDY DESIGN: Serial serum samples from 14 SARS patients were isolated from 7 to 210 days after the onset of the symptoms, and were tested for anti-viral IgG and IgM by indirect immunofluorescence tests (IFA), anti-nucleocaspid antibody by ELISA tests and viral neutralization. RESULTS: Anti-viral (IgG) and anti-nucleocaspid antibodies were observed in 13 of 14 patients at 14 days after the onset of symptoms, and in all 14 patients at 30-210 days thereafter. Anti-viral antibody (IgM) was detected maximally at 30 days, later than that for the IgG class. IgM antibody declined and became undetectable between 60 to 180 days after the onset of the symptoms. Neutralizing viral antibodies were demonstrated in the sera from all of the patients with SARS symptoms. CONCLUSIONS: Anti-viral IgG, IgM, and anti-nucleocaspid antibodies were detected 7-30 days in patients after the onset of SARS symptoms. Anti-viral IgM antibodies disappeared earlier than IgG. Viral neutralization was demonstrated in the sera from the convalescent patients.     

SARS患者特异性SARS-CoV抗体变化的观察

目的　研究SARS患者特异性SARS CoV抗体IgG、IgM动态变化规律 ,探讨机体感染SARS CoV后免疫应答的可能模式及流行病学意义 ,为科学的防治SARS提供理论依据。方法　ELISA测定北京地区最早感染SARS CoV的 3条传播链的SARS患者 4 7例 ,12 4份血清中SARS CoV特异性抗体IgG、IgM。其中 ,山西链 9人 ,13份血清 ;香港链 31人 ,84份血清 ;北京链 7人 ,2 7份血清。结果　 3条传播链SARS患者IgM阳性率 73% ,IgG阳性率 86 %。IgM最早于发病第 6天出现 ,阳性率高峰在病程 2～ 3周 ;持续时间短 ,1月后 6 0 %患者IgM逐渐阴转。IgG最早也可在发病第 6天出现 ,阳性率高峰在病程 3～ 4周 ,3月后IgG抗体阳性率减少。机体感染SARS CoV后 ,抗体出现有 3种模式。结论　机体感染SARS CoV后 ,近 90 %患者可出现特异性IgG ,病程 3～ 4周阳性率最高 ;特异性IgM抗体在病程2～ 3周阳性率最高 ,但多数只持续 2 0～ 30d。特异性IgG抗体表现 3种免疫应答模式。     

Diagnosis of severe acute respiratory syndrome (SARS) by detection of SARS coronavirus nucleocapsid antibodies in an antigen-capturing enzyme-linked immunosorbent assay

Recombinant severe acute respiratory syndrome (SARS) coronavirus nucleocapsid protein was employed to establish an antigen-capturing enzyme-linked immunosorbent assay (ELISA). Antinucleocapsid protein antibodies could be detected in 68.4% of probable SARS patients 6 to 10 days after illness and in 89.6% of the patients 11 to 61 days after illness. No false-positive results were observed in 20 non-SARS fever patients, 24 non-SARS respiratory illness patients, and 20 health care workers. Among 940 other non-SARS clinical serum samples, only 1 was found to be weakly positive. This method provides a new, sensitive, and specific approach for SARS diagnosis.     

Longitudinal profile of immunoglobulin G (IgG), IgM, and IgA antibodies against the severe acute respiratory syndrome (SARS) coronavirus nucleocapsid protein in patients with pneumonia due to the SARS coronavirus

By using a recombinant severe acute respiratory syndrome coronavirus (SARS-CoV) nucleocapsid protein-based enzyme-linked immunosorbent assay (ELISA) and serum specimens serially collected (from day 0 to day 240 after symptom onset) from patients with pneumonia due to SARS-CoV, we analyzed the longitudinal profiles of immunoglobulin G (IgG), IgM, and IgA antibodies against the SARS-CoV nucleocapsid protein in patients with pneumonia due to SARS-CoV. For IgG, the median optical density at 450 nm (OD450) turned positive at day 17 and a biphasic response was observed. At day 240, all patients were still positive for anti-nucleocapsid protein IgG antibody. For IgM, the median OD450 turned positive at day 20.5, peaked at about day 80, and fell to below the baseline level at about day 180. At day 240, 36% of the patients were still positive for anti-nucleocapsid protein IgM antibody. For IgA, the median OD450 turned positive at day 17, peaked at about day 50, and fell to below the baseline level at about day 180. At day 240, 36% of the patients were still positive for anti-nucleocapsid protein IgA antibody. The time of seroconversion detected by the recombinant SARS-CoV nucleocapsid protein-based ELISA and that detected by indirect immunofluorescence assay were similar. The median times of seroconversion for IgG, IgM, and IgA detected by the indirect immunofluorescence assay were 17 days (17 days by ELISA), 16.5 days (20.5 days by ELISA), and 17.5 days (17 days by ELISA), respectively, after disease onset. One, four, and one of the six patients who died did not produce any IgG, IgM, and IgA antibodies against the nucleocapsid protein of SARS-CoV, respectively, although these antibodies were detected in all six patients by the indirect immunofluorescence assay. Further studies should be performed to see whether SARS-CoV nucleocapsid protein antibody positivity has any prognostic significance.     

Longitudinal Profile of Immunoglobulin G (IgG), IgM, and IgA Antibodies against the Severe Acute Respiratory Syndrome (SARS) Coronavirus Nucleocapsid Protein in Patients with Pneumonia Due to the SARS Coronavirus

By using a recombinant severe acute respiratory syndrome coronavirus (SARS-CoV) nucleocapsid protein-based enzyme-linked immunosorbent assay (ELISA) and serum specimens serially collected (from day 0 to day 240 after symptom onset) from patients with pneumonia due to SARS-CoV, we analyzed the longitudinal profiles of immunoglobulin G (IgG), IgM, and IgA antibodies against the SARS-CoV nucleocapsid protein in patients with pneumonia due to SARS-CoV. For IgG, the median optical density at 450 nm (OD₄₅₀) turned positive at day 17 and a biphasic response was observed. At day 240, all patients were still positive for anti-nucleocapsid protein IgG antibody. For IgM, the median OD₄₅₀ turned positive at day 20.5, peaked at about day 80, and fell to below the baseline level at about day 180. At day 240, 36% of the patients were still positive for anti-nucleocapsid protein IgM antibody. For IgA, the median OD₄₅₀ turned positive at day 17, peaked at about day 50, and fell to below the baseline level at about day 180. At day 240, 36% of the patients were still positive for anti-nucleocapsid protein IgA antibody. The time of seroconversion detected by the recombinant SARS-CoV nucleocapsid protein-based ELISA and that detected by indirect immunofluorescence assay were similar. The median times of seroconversion for IgG, IgM, and IgA detected by the indirect immunofluorescence assay were 17 days (17 days by ELISA), 16.5 days (20.5 days by ELISA), and 17.5 days (17 days by ELISA), respectively, after disease onset. One, four, and one of the six patients who died did not produce any IgG, IgM, and IgA antibodies against the nucleocapsid protein of SARS-CoV, respectively, although these antibodies were detected in all six patients by the indirect immunofluorescence assay. Further studies should be performed to see whether SARS-CoV nucleocapsid protein antibody positivity has any prognostic significance.     

A serological survey on neutralizing antibody titer of SARS convalescent sera

A seroepidemiologic study was conducted in North China in 2003 to determine the neutralizing antibody titer of severe acute respiratory syndrome (SARS) convalescent sera. A total of 99 SARS convalescent serum samples were collected from patients from the Inner Mongolia Autonomous Region, Hebei Province, and Beijing 35-180 days after the onset of symptoms. The anti-SARS antibodies were detected by enzyme-linked immunosorbent assay (ELISA), neutralization assay, and Western blot. Eighty-seven serum samples were confirmed to be positive for SARS antibodies. The neutralizing antibody titer of the 87 positive sera was analyzed quantitatively by neutralization assay. The geometric mean titer (GMT) of the 87 convalescent sera was 1:61. The Kolmogorov-Smirnov test showed that the neutralizing antibody titers conform to normal distribution, which suggests that the average anti-SARS antibody level in this study was representative of the convalescent antibody level of the SARS population. This result could be useful for the development and quality control of SARS vaccines.     

Evaluation of antibody responses against SARS coronaviral nucleocapsid or spike proteins by immunoblotting or ELISA

Severe acute respiratory syndrome (SARS)-CoV is a newly emerging virus that causes SARS with high mortality rate in infected people. To study the humoral responses against SARS-CoV, we evaluated nucleocapsid (N) and spike (S) proteins-specific antibodies in patients' sera by Western blotting and enzyme-linked immunosorbent assay (ELISA). Recombinant N and S proteins of SARS-CoV were purified from transformed E. coli. Serum specimens from 40 SARS-CoV-infected patients in the convalescent phase were analyzed by Western blotting using the purified antigens. Serial serum specimens from 12 RT-PCR-confirmed SARS patients were assayed by ELISA using the recombinant N protein as coated antigen. By Western blotting, 97.5% of the SARS patients were positive for N protein-specific antibodies whereas only 47.5% of the samples were positive for S protein-specific antibodies. Using N protein-based ELISA, 10 out of the 12 patients were positive for N protein-specific antibodies and 6 of them showed seroconversion at mean of 16 days after onset of fever. Immunoblotting was useful for detecting the humoral immune response after SARS-CoV infection. Antibodies against SARS-CoV N protein appear at the early stage of infection, therefore, N protein-based ELISA could serve as a simple, sensitive, and specific test for diagnosing SARS-CoV infection.     

Persistent shedding of viable SARS-CoV in urine and stool of SARS patients during the convalescent phase

In order to further the present knowledge of the emerging severe acute respiratory syndrome-associated coronavirus (SARS-CoV), 486 different specimens from 54 patients with a clinical diagnosis of SARS were investigated for the presence of viral RNA, and 314 plasma specimens of 73 patients were examined for IgM and IgG antibodies specific against SARS-CoV using an indirect ELISA. Viral RNA was detectable in 28 of the 54 patients tested. Cumulative data showed that 67 of the 73 SARS patients demonstrated seroconversion by week 5 of illness. In contrast, only 1 of 278 healthy subjects enrolled in the study was found to be positive for the IgG antibody. Coexistence of viral RNA in plasma and specific antibodies was simultaneously observed over three consecutive weeks in two critical cases. In three convalescent patients in particular, cultivable SARS-CoV was detected in stool or urine specimens for longer than 4 weeks (29–36 days). These findings suggest that SARS-CoV may remain viable in the excretions of convalescent patients.     

SARS相关冠状病毒M蛋白基因重组核酸疫苗的实验研究

目的：构建针对SAILS相关冠状病毒M蛋白基因的重组核酸疫苗，观察其免疫小鼠后肌体的抗体产生情况，探讨其作为抗SAILS病毒疫苗的可能性。方法：通过分子生物学的方法构建SARS相关冠状病毒M蛋白基因真核表达质粒pcDNA3．1／M。经肌注免疫健康BALB／c小鼠，在免疫后的2．4、6周取小鼠血清，用ELISA法检测其中的抗体。结果：接种含M基因的真核表达质粒pcDNA3．1／M的低剂量组和高剂量组的小鼠血清在接种2周后就可检测出SARS-CoV特异性IgG，第4周时，这种特异性IgG水平有升高趋势，第6周时，血清中的抗体含量与4周时无大的差异。高剂量组产生抗体与低剂量组产生抗体无显著差异。pcDNA3．1空载体接种的对照组未检测出特异性抗体（其OD值低于0．18）。结论：构建的真核表达质粒pcDNA3．1／M能诱导小鼠产生了针对SARS的抗体。     

An animal model of SARS produced by infection of Macaca mulatta with SARS coronavirus

A new SARS animal model was established by inoculating SARS coronavirus (SARS-CoV) into rhesus macaques (Macaca mulatta) through the nasal cavity. Pathological pulmonary changes were successively detected on days 5-60 after virus inoculation. All eight animals showed a transient fever 2-3 days after inoculation. Immunological, molecular biological, and pathological studies support the establishment of this SARS animal model. Firstly, SARS-CoV-specific IgGs were detected in the sera of macaques from 11 to 60 days after inoculation. Secondly, SARS-CoV RNA could be detected in pharyngeal swab samples using nested RT-PCR in all infected animals from 5 days after virus inoculation. Finally, histopathological changes of interstitial pneumonia were found in the lungs during the 60 days after viral inoculation: these changes were less marked at later time points, indicating that an active healing process together with resolution of an acute inflammatory response was taking place in these animals. This animal model should provide insight into the mechanisms of SARS-CoV-related pulmonary disease and greatly facilitate the development of vaccines and therapeutics against SARS.     

严重急性呼吸综合征自身免疫指标的初步研究

目的　探讨严重急性呼吸综合征(SARS)患者是否存在着自身免疫现象,寻找患者体内异常出现的抗自身组织器官的抗体。方法　随机选取2 7例SARS患者及18例健康献血员对照血清同时应用免疫荧光法检测抗核抗体(ANA)、抗平滑肌抗体(SMA)、抗线粒体抗体(AMA)、抗胃壁细胞抗体(PCA)、抗心肌抗体(HRA) ,应用酶联免疫吸附试验(ELISA)检测抗肝肾微粒体抗体(LKM)及抗线粒体M2亚型抗体,同时利用猴肺组织基质片应用免疫荧光法定位血清中的SARS相关抗体的靶细胞。结果　2 7例SARS患者中有3例ANA阳性、1例SMA阳性、1例AMA阳性、1例LKM阳性、其余均为阴性;18例献血员中有1例ANA阳性、1例AMA阳性,其余均为阴性。统计分析表明SARS患者与献血员间各项自身抗体阳性率差异均不具有统计学意义。在2 7例SARS患者血清中有2 6例在肺组织细小支气管柱状上皮细胞的腔面尖端呈现强阳性荧光信号,献血员中有5例,统计分析表明两者阳性率差异有统计学意义。结论　SARS患者未出现抗肺外组织、器官的自身抗体。患者血清中出现了抗肺组织的自身抗体,定位于细小支气管柱状上皮细胞。     

重组冠状病毒核衣壳蛋白血清抗体检测

目的 SARS冠状病毒的核衣壳(Nucleocapsid)蛋白(N蛋白)是病毒的主要结构抗原，重组N蛋白可用作抗原检测患者血清中相应抗体。方法 以纯化的目的蛋白N-1，N-2分别包被96孔板，检测正常人群及患者血清中抗SAKS病毒抗体。结果 检测SAKS感染患者血清，N-1阳性检出率为55．68％，N-2阳性检出率为56．82％，与华大基因试剂盒相比符合率分别为90．12％和87．65％。结论 重组核衣壳蛋白可做为检测SARS抗体的抗原蛋白。     

严重急性呼吸综合征患者IgG抗体的研究

目的　探讨血清特异性IgG抗体检测对严重急性呼吸综合征 (SARS)临床诊断的意义及影响因素。方法　用华大公司研制的SARS冠状病毒抗体 (IgG)酶联免疫试剂盒 ,对部分住院SARS患者的血清进行IgG抗体检测 ,统计分析不同年龄、性别和激素使用患者的SARS特异性抗体的产生情况。结果　在确诊的 12 1例患者中 ,IgG抗体阳性率为 71 1% ,年龄 <15岁、15～ 5 9岁和 6 0岁以上的患者 ,阳性检测率分别为 6 0 0 %、70 2 %和 85 7% ,差异无显著意义 (P =0 76 6 ) ;使用激素和不使用激素的患者 ,阳性率分别为 70 6 %和 72 4 % (P =0 84 ) ;病重和病情较轻患者的阳性检测率分别为78 1%和 6 7 4 % (P =0 4 93) ;男性和女性患者检测率均为 71 1%。结论　SARS特异性IgG抗体检测的敏感性有待进一步提高 ,IgG抗体的产生与性别、年龄、病情轻重和激素的使用无显著性关系。     

传播链和非传播链SARS患者中SARS冠状病毒抗体的分布及变化规律

目的　探讨人体对SARS CoV血清抗体反应及分布规律。方法　对 30 1例临床诊断病例的血清标本 (其中传播链上的病例 15 8例 ,非传播链病例 14 3例 ) ;采用北京华大GBI生物技术有限公司生产的间接ELISA试剂 ,进行SARS CoVIgG抗体的检测 ,部分病例还进行了SARS CoVIgM的检测。结果　传播链涉及 15条 ,最多涉及 4代 ,各条链的SARSIgG抗体阳性率为 85 70 %～ 10 0 .0 0 % ,总阳性率为 94 30 % (14 9 15 8)。SARS病例数随代数增加而减少。但各代间IgG阳性率的差异无显著意义 ;χ2 =5 11,P >0 0 5。非传播链病例的血清抗体阳性率为 12 5 9% (18 14 3)。与传播链的阳性率比较 ,两者间的差异有显著意义 ;χ2 =199 6 4 ,P <0 0 0 1。在发病后的 0～ 7d、8～ 14d、15～ 2 1d、2 2～ 30d内 ,SARS CoVIgG的累计阳性率分别为 16 6 7%、4 0 0 0 %、70 0 0 %、93 10 % ;然后进入平台期 ,并可以维持 6个月以上。在发病 7d内 ,SARS CoVIgM的累计阳性率为 16 6 7% ,8～ 14d时 ,已有 5 5 17%的标本IgM抗体阳转 ,在 2 1～ 30d时 ,抗体阳性率达高峰 (86 96 % ) ,以后迅速下降。结论　SARS感染后 ,94 %的感染者可产生IgG抗体。检测该抗体可以作为临床核实诊断的依据。SARS CoVIgG抗体在 7d时可能检出 ,一般在 4周达     

Identification of a critical neutralization determinant of severe acute respiratory syndrome (SARS)-associated coronavirus: importance for designing SARS vaccines

The spike (S) protein of severe acute respiratory syndrome-associated coronavirus (SARS-CoV) is not only responsible for receptor binding, but also a major antigenic determinant capable of inducing protective immunity. In this study, we demonstrated that the receptor-binding domain (RBD) of S protein is an important immunogenic site in patients with SARS and rabbits immunized with inactivated SARS-CoV. Serum samples from convalescent SARS patients and immunized rabbits had potent neutralizing activities against infection by pseudovirus expressing SARS-CoV S protein. Depletion of RBD-specific antibodies from patient or rabbit immune sera by immunoadsorption significantly reduced serum-mediated neutralizing activity, while affinity-purified anti-RBD antibodies had relatively higher potency neutralizing infectivity of SARS pseudovirus, indicating that the RBD of S protein is a critical neutralization determinant of SARS-CoV during viral infection and immunization. Two monoclonal antibodies (1A5 and 2C5) targeting at the RBD of S protein were isolated from mice immunized with inactivated SARS-CoV. Both 1A5 and 2C5 possessed potent neutralizing activities, although they directed against distinct conformation-dependant epitopes as shown by ELISA and binding competition assay. We further demonstrated that 2C5, but not 1A5, was able to block binding of the RBD to angiotensin-converting enzyme 2 (ACE2), the functional receptor on targeted cells. These data provide important information for understanding the antigenicity and immunogenicity of SARS-CoV and for designing SARS vaccines.     

Longitudinal analysis of Severe Acute Respiratory Syndrome (SARS) coronavirus-specific antibody in SARS patients

The serum antibodies to severe acute respiratory syndrome (SARS) coronavirus of 18 SARS patients were checked at 1 month and every 3 months after disease onset. All of them except one, who missed blood sampling at 1 month, tested positive for the immunoglobulin G (IgG) antibody at 1 month. Fifteen out of 17 tested positive for the IgM antibody at 1 month. The serum IgM antibody of most patients became undetectable within 6 months after the onset of SARS. The IgG antibody of all 17 patients, whose serum was checked 1 year after disease onset, remained positive.     

Longitudinal Analysis of Severe Acute Respiratory Syndrome (SARS) Coronavirus-Specific Antibody in SARS Patients

The serum antibodies to severe acute respiratory syndrome (SARS) coronavirus of 18 SARS patients were checked at 1 month and every 3 months after disease onset. All of them except one, who missed blood sampling at 1 month, tested positive for the immunoglobulin G (IgG) antibody at 1 month. Fifteen out of 17 tested positive for the IgM antibody at 1 month. The serum IgM antibody of most patients became undetectable within 6 months after the onset of SARS. The IgG antibody of all 17 patients, whose serum was checked 1 year after disease onset, remained positive.