Respiratory tract protection upon challenge of pigs vaccinated with attenuated porcine reproductive and respiratory syndrome virus vaccines

In this study, the efficacy of two attenuated porcine reproductive and respiratory syndrome virus (PRRSV) vaccines was assessed. The virological protection in the lungs of vaccinated pigs upon challenge was studied. Also, challenged pigs were exposed to lipopolysaccharide (LPS) to evaluate clinical protection. Six-week-old pigs were immunized intramuscularly with commercial vaccines based on either an attenuated American or an attenuated European virus strain. Non-immunized pigs and pigs intramuscularly inoculated with the virulent Lelystad strain were included as controls. Six weeks after immunization, pigs were challenged either intratracheally or intranasally with the Lelystad strain, and 3 and 6 days later intratracheally exposed to Escherichia coli LPS. After LPS administration, pigs were monitored for clinical signs. At 4 and 7 days after challenge, pigs were euthanized to determine virus quantities in broncho-alveolar lavage (BAL) fluids and in lungs. Challenge virus was recovered from three out of eight pigs that had been primo-inoculated with the Lelystad strain with titers ranging between 0.3 and 3.1 log(10). Fifteen out of sixteen pigs vaccinated with the attenuated American strain were positive for challenge virus and their mean virus titers were similar to those of non-immunized challenge controls. Eleven out of 16 pigs vaccinated with the attenuated European strain were positive for challenge virus and their mean virus titers were 2.0-2.5 log(10) lower than those of non-immunized challenge controls. Thus, the virological protection in the lungs of vaccinated pigs upon challenge was incomplete, but was more pronounced in the homologous situation. Clinical signs upon LPS exposure in both vaccinated groups were not reproducible in two experiments.     

黄芪多糖和白花蛇舌草多糖对猪高致病性繁殖与呼吸综合征灭活疫苗免疫的影响

以黄芪多糖和白花蛇舌草多糖作为免疫增强剂联合猪高致病性繁殖与呼吸综合征灭活疫苗免疫26日龄断奶仔猪,免疫后7,14,24,34,44,54,69 d前腔静脉采血,检测外周血淋巴细胞增殖,并用ELISA法检测血清中抗猪繁殖与呼吸综合征病毒抗体及IL-2水平.结果表明,与生理盐水组比较,黄芪多糖和白花蛇舌草多糖均能极显著促进外周血淋巴细胞的增殖,使抗体提早产生并提高抗体滴度和IL-2表达水平;因此,黄芪多糖和白花蛇舌草多糖能增强猪对高致病性繁殖与呼吸综合征灭活疫苗的免疫应答能力.     

Efficacy of Fostera PRRS modified live virus vaccine against a Canadian heterologous virulent field strain of porcine reproductive and respiratory syndrome virus

Vaccination is a useful option to control infection with porcine reproductive and respiratory syndrome virus (PRRSV), and several modified live-PRRSV vaccines have been developed. These vaccines have shown some efficacy in reducing the incidence and severity of clinical disease as well as the duration of viremia and virus shedding but have failed to provide sterilizing immunity. The efficacy of modified live-virus (MLV) vaccines is greater against a homologous strain compared with heterologous PRRSV strains. The objective of this study was to evaluate the efficacy of Fostera PRRS MLV vaccine in protecting against challenge with a heterologous field strain widely circulating in the swine herds of eastern Canada. Forty-six piglets were divided into 4 groups: nonvaccinated-nonchallenged; nonvaccinated-challenged; vaccinated-challenged; and vaccinated-nonchallenged. The animals were vaccinated at 23 d of age with Fostera PRRS and challenged 23 d later with a heterologous field strain of PRRSV (FMV12-1425619). Overall, the vaccine showed some beneficial effects in the challenged animals by reducing the severity of clinical signs and the viral load. A significant difference between nonvaccinated and vaccinated animals was detected for some parameters starting 11 to 13 d after challenge, which suggested that the cell-mediated immune response or other delayed responses could be more important than pre-existing PRRSV antibodies in vaccinated animals within the context of protection against heterologous strains.     

猪繁殖与呼吸综合征病毒弱毒株活疫苗抗体应答水平的观察

用本厂生产的猪繁殖与呼吸综合征(PRRS)活疫苗及病毒液分别以不同剂量给PRRS阴性猪注射，并在不同时间采血测其相应的抗体水平，比较不同剂量抗体水平维持时间。结果表明，猪注射该疫苗后14d即可产生较高的抗体水平，并在21—35d达到高峰，42d略有下降，70d时抗体水平仍为阳性，104d仍有85％以上的猪抗体水平阳性。     

An attenuated live vaccine based on highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) protects piglets against HP-PRRS

Porcine infections with highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) cause significant morbidity and mortality and currently there are no effective vaccines for disease prevention. An attenuated strain, HuN4-F112, was obtained by passaging the HP-PRRSV HuN4 on Marc-145 cells (112th-passage). PRRSV-free pigs were inoculated intramuscularly with HuN4-F112 (10^2.0, 10^3.0, 10^4.0, 10^5.0 and 10^6.0 TCID₅₀ for groups 1–5, respectively). The groups 3–5 could resist the lethal challenge and did not show any obvious changes in body temperature nor clinical signs throughout the experiment, the pathological lesions were milder and the gained weight at a greater rate (P < 0.05), compared to group 1 and control. Sequence analysis of the HuN4 passages showed a conserved epitope in GP5 protein was mutated (¹⁹⁶QWGRL/P²⁰⁰ → ¹⁹⁶RWGRL/P²⁰⁰), as a result the monoclonal antibody could not recognize the HuN4-F112 any more. These results suggested that the HuN4-F112 could protect piglets from lethal challenge and might be a candidate vaccine against the HP-PRRSV.     

猪繁殖与呼吸综合征弱毒疫苗研究进展

<正>经典的猪繁殖与呼吸综合征(PRRS)是一种主要表现为母猪繁殖障碍与新生仔猪呼吸道症状的传染病。近年来,国内新暴发和流行的高致病性PRRS,则以高热、高     

不同猪繁殖与呼吸综合征减毒活疫苗在猪体内的动态学及临床免疫效果比较

为了比较国内不同猪繁殖与呼吸综合征(porcine reproductive and respiratory syndrome,PRRS)弱毒疫苗的安全性和有效性,本研究将17头PRRSV抗原和抗体双阴性的28日龄仔猪随机分为4组,TJM-F92株弱毒疫苗组,JXA1-R株弱毒疫苗组,经典株弱毒疫苗(VR2332来源)组和注射生理盐水对照组。免疫后7,14,21,28d分别采血,ELISA抗体检测试剂盒检测PRRSV抗体,结果从免疫后14d起PRRSV抗体开始转阳,但各试验组的抗体水平无明显差异。对免疫后14d所采血样进行病毒分离,TJM-F92株免疫组未分离到PRRSV疫苗毒,JXA1-R株免疫组2头猪分离到PRRSV疫苗毒,经典株免疫组只1头猪分离到PRRSV疫苗毒。免疫后28d,所有猪接种PRRSV强毒株TJ株进行攻毒试验,观察各组猪的体温、临床症状;攻毒后21d,所有猪安乐死,剖检观察肺部病理变化。结果显示,TJM-F92株和JXA1-R株免疫组均未出现临床发病猪,经典株免疫组2头猪出现临床发病,对照组全部临床发病,死亡1头。经典株免疫组临床发病猪出现典型PRRSV感染肺部病理变化,而TJM-F92株和JXA1-R株免疫组均未发现典型PRRSV感染肺部病理变化。本研究证实TJM-F92株和JXA1-R株对高致病性PRRSV的免疫效果优于经典株弱毒疫苗,TJM-F92疫苗株与JXA1-R疫苗株相比,疫苗毒在体内带毒时间更短,安全性更高。     

Effect of the host cell line on the vaccine efficacy of an attenuated porcine reproductive and respiratory syndrome virus

The abilities of the modified-live Prime Pac (PP) strain of porcine reproductive and respiratory syndrome virus (PRRSV), propagated in either traditional simian cells (MARC-145) or in a novel porcine alveolar macrophage cell line (ZMAC), to confer pigs protection against subsequent PRRSV challenge were compared. Eight week-old pigs were injected with PP virus grown in one of the two cell types and then exposed 4 weeks later to the "atypical" PRRSV isolate NADC-20. Control animals were similarly challenged or remained PRRSV-na?ve. While the average adjusted body weight (aabw) of the strict control group increased 22% by 10 days post challenge (pc), this value for the non-vaccinated, challenged group dropped 4%. In contrast, prior immunization with PP virus, regardless of its host cell source, ameliorated this effect by affording a >9% rise in aabw. Likewise, nearly equivalent protection was extended to both groups of vaccinates in regards to the temporal elimination of their pc clinical distress and viremia. However, the PP virus propagated in ZMAC cells appeared to be more efficacious since four of the six pigs receiving this biologic cleared the challenge virus from the their lungs by 10 days pc as compared to only one member of the other vaccinated group. Notably, the predominant quasispecies in the ZMAC cell-prepared PP virus stock contained a highly conserved N-glycosylation site at position 184 in its glycoprotein 2 while this entity was underrepresented in the MARC-145 cell grown biologic. Since glycoprotein 2 is involved in infectivity, such additional glycosylation may enhance virus replication in porcine alveolar macrophages.     

Immune responses and protection by vaccine and various vaccine adjuvant candidates to virulent porcine reproductive and respiratory syndrome virus

Various vaccine adjuvant candidates were assessed with the modified-live porcine reproductive and respiratory syndrome virus (MLV PRRSV) (Ingelvac PRRS MLV) vaccine. Their influence on humoral-mediated immune (HMI) and cell-mediated immune (CMI) responses as well as protection from virulent PRRSV challenge (MN-184) was evaluated. Ninety seronegative pigs were randomly divided into nine groups of 10 pigs. One group received MLV vaccine alone. Five groups received MLV vaccine with either bacterial endotoxin-derived adjuvant (ET), mixed open reading frame 5 (ORF5) peptides derived from various PRRSV isolates, porcine interferon alpha (IFNalpha), polyinosinic-polycytidylic acid stabilized with polylysine and carboxymethylcellulose (poly-ICLC), or porcine interleukin-12 (IL-12). One group did not receive MLV vaccine but was immunized with ORF5 peptides conjugated with cholera toxin (ORF5 peptide/CT). Two groups served as challenged and unchallenged non-vaccinated controls. Four-color flow cytometry was utilized to simultaneously identify three major porcine T-cell surface markers (CD4, CD8, and gammadelta TCR) and detect activation marker CD25 (alpha chain of IL-2 receptor) or intracellular IFNgamma. The MLV PRRSV vaccine alone successfully primed CD4(-)CD8(+)gammadelta- T-cells as demonstrated by a significant increase in %IFNgamma+ cells when live PRRSV was used as a recall antigen. Booster immunizations of mixed ORF5 peptides and co-administration of IL-12 with MLV PRRSV vaccine significantly enhanced IFNgamma expression by some T-cell subsets (CD4(-)CD8(+)gammadelta+ and CD4(-)CD8(-)gammadelta+ for mixed ORF5 peptides and CD4(+)CD8(+)gammadelta- and CD4(-)CD8(+)gammadelta+ for IL-12). All groups receiving MLV-vaccine with or without adjuvants had reduced lung lesions after challenge. The group immunized with only ORF5 peptide/CT did not have significant T-cell recall responses and was not protected from challenge. Expression of IFNgamma by several T-cell subsets correlated with reduced lung lesions and viremia, whereas expression of CD25 did not. Expression of surface CD25 did not correlate with IFNgamma production. PRRSV ELISA s/p ratio prior to challenge also correlated with reduced lung lesions and viremia. In conclusion, booster immunizations of the mixed ORF5 peptides and co-administration of IL-12 effectively enhanced the CMI response to MLV vaccine. However, neither adjuvant significantly contributed to reducing clinical effects when compared to MLV alone.     

猪繁殖与呼吸综合征病毒R98弱毒株的分离鉴定与ORFs3～7基因特性研究

应用特异性引物从猪血凝性脑脊髓炎病毒（HEV）中扩增出S1蛋白基因,PCR产物纯化后克隆入pGEM-T载体中,得到重组质粒pTS1。用EcoRI和Not I双酶切pTS1,回收目的基因S1片段将其定向克隆到pPICZαA中,构建重组质粒pPICZαAS1。用BstXI酶切pPICZαAS1使其线性化,并电转至感受态毕赤酵母细胞GS115。PCR法鉴定阳性重组子,用1%甲醇诱导表达后,进行SDS-PAGE及Western blot分析。结果显示,在酵母菌培养基上清中检测到相对分子质量为73000的重组蛋白,且该重组蛋白可与HEV多克隆抗体发生特异性血清学反应,表明HEV的S1蛋白片段在毕赤酵母中获得成功表达。     

猪繁殖-呼吸综合征活疫苗对仔猪的安全性试验

本试验用猪繁殖-呼吸综合征（PRRS）活疫苗和国内分离的PRRS强毒CH—1a株接种PRRS阴性的断奶仔猪，分别在接种后的3、7、14d各剖杀1头，取各脏器分别做冰冻切片和病理切片观察。用间接免疫荧光法检测各脏器PRRS病毒的分布。结果表明，PRRS活疫苗在免疫初期，抗原主要分布在脾脏、淋巴结，其次是肾脏和肺脏，少见于肝脏和心脏，第14d时在脾、淋巴结和肾脏有一定量的抗原，而肺脏相比则数量很少，肝脏和心脏未检到PRRS病毒抗原的存在，表明接种PRRS活疫苗随着时间的推移抗原分布呈下降趋势。而强毒抗原分布以脾脏最多，依次是肾脏、肺脏、淋巴结、肝脏、心脏，接种后第14d仍能在各脏器检到PRRS病毒抗原。病理组织学检测结果表明，活疫苗产生以下颌淋巴结、脾脏增生为特征的免疫应答，组织损伤轻微，对肺的病变较少，且仔猪生长良好。强毒则引起以大面积的肺泡隔增宽为特点的间质性肺炎和微循环障碍的病理变化，淋巴小结、脾脏滤泡发生崩解与周围界限不清，个别淋巴细胞核浓缩，组织损伤严重。本试验表明弱毒疫苗对仔猪是安全的。     

一株猪繁殖与呼吸综合征病毒的分离鉴定

为了对从湖南某发病猪场送检的血清中分离到的1株蓝耳病病毒进行鉴定,试验通过接种Marc-145细胞传代后产生明显而稳定的细胞病变,又经过RT-PCR及间接免疫荧光(IFA)检测成功验证;通过对分离株的ORF5基因的测序结果表明,ORF5核苷酸序列与欧洲型代表株LV株及北美经典毒株VR-2332、国内经典美洲株CH-1a的相似性分别为64.5%、87.4%、93.0%,说明其属于美洲型;而将NSP2高变区的测序结果与JXA1等高致病性变异株的Nsp2比较后发现,都在同一位置不连续缺失30个氨基酸。说明成功分离到1株北美型变异株,最终将其命名为PRRSV CZ-HN株。     

Immune responses in piglets infected with highly pathogenic porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) infection compromises the host's innate and adaptive immunity. The aim of this study was to investigate the immune responses of piglets infected with highly pathogenic (HP) PRRSV (HuN4 strain) with or without the immunization with CH-1R attenuated PRRSV vaccine. The response was evaluated for the clinical signs, pathological changes and virus load in immune organs, antibody responses and levels of serum IFN-γ, IL-4 and IL-10. The result showed that in comparison with the piglets received the immunization, the piglets infected with HP-PRRSV alone had the thymus atrophy, decreased serum levels of IL-4 and increased serum levels of IL-10 and INF-γ. These results suggest that elevated IL-10 levels at the early stage of the infection may enhance virus survival and delay the induction of protective immunity, while increased levels of IL-4 induce the effective immune responses and increase the animals' health status.     

Failure of an inactivated vaccine against porcine reproductive and respiratory syndrome to protect gilts against a heterologous challenge with PRRSV

This study was designed to evaluate the efficacy of an inactivated vaccine based on a European-type strain of porcine reproductive and respiratory syndrome virus (PRRSV) against the reproductive form of the syndrome in breeding gilts, and any congenital disease in their piglets. Five gilts were vaccinated twice, following the manufacturer's instructions, before they were inseminated. Nine additional gilts remained unvaccinated and served as positive (five gilts) and negative (four gilts) controls. A European wild-type strain genetically divergent from the vaccine strain was used to challenge the five vaccinated and five unvaccinated positive control gilts at 90 days' gestation. The vaccination of the five seronegative gilts did not produce any clinical signs or adverse reactions. However, the vaccine failed to prevent the clinical signs associated with PRRSV infection, viraemia after the challenge and transplacental infection of their piglets. The reproductive performance of the vaccinated gilts was similar to that of the unvaccinated positive controls, and there were no statistically significant differences in most of the parameters tested. However, the preweaning mortality of the piglets born to the vaccinated gilts was significantly lower than that of the piglets born to the positive control gilts.     

猪圆环病毒和猪繁殖与呼吸综合征病毒混合感染对仔猪致病性的评估

本研究通过猪圆环病毒2型(Porcine circovirus type 2,PCV2)和猪繁殖与呼吸综合征(Porcine reproductive and respiratory syndrome virus,PRRSV)强毒共感染3周龄健康仔猪来评价其致病性。试验动物随机分为3组,空白对照组(n=3头),PRRSV单独感染组(n=3头),PCV2和PRRSV共感染组(n=6头),从而比较相互之间的差异。通过临床症状、病理学变化、病原学和血清学检查,对二者混合感染仔猪的致病性进行了研究。结果表明PCV2和PRRSV共同感染能引起仔猪断奶后多系统消耗性综合征,表现为淋巴组织肿大、出血,肉芽肿性炎症,坏死性肝炎,仔猪消瘦、生长缓慢等特征性病变;混合感染能加重PRRSV对仔猪引起的间质性肺炎的严重程度。混合感染可以出现支气管肺炎和明显的肝病变,淋巴结多呈界限明显的块状出血等典型病变。     

Genetic and immunobiological diversities of porcine reproductive and respiratory syndrome genotype I strains

Genetic diversity of porcine reproductive and respiratory syndrome virus (PRRSV) has been based on ORF5/GP5 and ORF7/N protein variations. Complete viral genome studies are limited and focused on a single or a few set of strains. Moreover, there is a general tendency to extrapolate results obtained from a single isolate to the overall PRRSV population. In the present study, six genotype-I isolates of PRRSV were sequenced from ORF1a to ORF7. Phylogenetic comparisons and the variability degree of known linear B-epitopes were done considering other available full-length genotype-I sequences. Cytokine induction of all strains was also evaluated in different cellular systems. Non structural protein 2 (nsp2) was the most variable part of the virus with 2 out of 6 strains harboring a 74 aa deletion. Deletions were also found in ORF3 and ORF4. Phylogenetic analyses showed that isolates could be grouped differently depending on the ORF examined and the highest similarity with the full genome cluster was found for the nsp9. Interestingly, most of predicted linear B-epitopes in the literature, particularly in nsp2 and GP4 regions, were found deleted or varied in some of our isolates. Moreover, 4 strains, those with deletions in nsp2, induced TNF-α and 3 induced IL-10. These results underline the high genetic diversity of PRRSV mainly in nsp1, nsp2 and ORFs 3 and 4. This variability also affects most of the known linear B-epitopes of the virus. Accordingly, different PRRSV strains might have substantially different immunobiological properties. These data can contribute to the understanding of PRRSV complexity.     

2株猪繁殖与呼吸综合征病毒毒株对仔猪致病性的比较

为了比较最新分离的猪繁殖与呼吸综合征病毒(PRRSV)变异分离株SY0608和传统毒株S1对仔猪的致病性,本研究选择9头30日龄商品仔猪,随机分为2组,分别接种2株病毒,即S1株感染组(n=5头),SY0608株感染组(n=4头),接种后隔离饲养观察2周。经临床症状观察、病理学、病原学和血常规学检查,结果:SY0608毒株感染组仔猪表现明显临床症状,接种3 d后体温急剧升高至41.8℃;白细胞数急剧减少(降低了45%);病理学变化严重,肺泡膈增宽,大部分肺组织肺泡不张;而S1株感染组仔猪仅出现轻微临床症状和病理变化。SY0608毒株感染组仔猪病毒血症持续时间较S1毒株感染组长,病毒在脏器中的分布更为广泛。SY0608株感染组血清ELISA抗体水平明显高于S1株感染组。结果表明,SY0608毒株对仔猪致病作用明显强于S1毒株。     

Evidence for a major QTL associated with host response to porcine reproductive and respiratory syndrome virus challenge

Porcine reproductive and respiratory syndrome (PRRS) causes decreased reproductive performance in breeding animals and increased respiratory problems in growing animals, which result in significant economic losses in the swine industry. Vaccination has generally not been effective in the prevention of PRRS, partially because of the rapid mutation rate and evolution of the virus. The objective of the current study was to discover the genetic basis of host resistance or susceptibility to the PRRS virus through a genome-wide association study using data from the PRRS Host Genetics Consortium PRRS-CAP project. Three groups of approximately 190 commercial crossbred pigs from 1 breeding company were infected with PRRS virus between 18 and 28 d of age. Blood samples and BW were collected up to 42 d post infection (DPI). Pigs were genotyped with the Illumina Porcine 60k Beadchip. Whole-genome analysis focused on viremia at each day blood was collected and BW gains from 0 to 21 DPI (WG21) or 42 DPI (WG42). Viral load (VL) was quantified as area under the curve from 0 to 21 DPI. Heritabilities for WG42 and VL were moderate at 0.30 and litter accounted for an additional 14% of phenotypic variation. Genomic regions associated with VL were found on chromosomes 4 and X and on 1, 4, 7, and 17 for WG42. The 1-Mb region identified on chromosome 4 influenced both WG and VL, exhibited strong linkage disequilibrium, and explained 15.7% of the genetic variance for VL and 11.2% for WG42. Despite a genetic correlation of -0.46 between VL and WG42, genomic EBV for this region were favorably and nearly perfectly correlated. The favorable allele for the most significant SNP in this region had a frequency of 0.16 and estimated allele substitution effects were significant (P < 0.01) for each group when the SNP was fitted as a fixed covariate in a model that included random polygenic effects with overall estimates of -4.1 units for VL (phenotypic SD = 6.9) and 2.0 kg (phenotypic SD = 3 kg) for WG42. Candidate genes in this region on SSC4 include the interferon induced guanylate-binding protein gene family. In conclusion, host response to experimental PRRS virus challenge has a strong genetic component, and a QTL on chromosome 4 explains a substantial proportion of the genetic variance in the studied population. These results could have a major impact in the swine industry by enabling marker-assisted selection to reduce the impact of PRRS but need to be validated in additional populations.     

Some characteristics of four attenuated vaccine virus strains and a virulent strain of Aujeszky's disease virus

In the present study four attenuated virus strains, used as vaccines, and a virulent strain of Aujeszky's disease virus (ADV) were compared with respect to their virulence in mice, their ability to induce virus-specified thymidine kinase (TK) in infected cells, and their cleavage profiles of viral DNA's after treatment with the restriction endonuclease KpnI. The survival time of mice inoculated with the B-KAL or the virulent NIA-3 strain was comparable, whereas the Bartha and BUK strains required significantly longer periods to kill mice. Mice were resistant to the MK-25 strain of ADV. The strains were assayed for TK phenotype by plaque autoradiography after 3H-thymidine labelling of infected cells. MK-25 proved to be the only strain defective in induction of TK in pig kidney cells. Restriction endonuclease analysis of viral DNA's revealed that each vaccine strain showed a characteristic fragment pattern that could easily be differentiated from that of other vaccine and field strains of ADV. The present results demonstrate that the mouse virulence test and the TK assay detect differences in biological properties of ADV strains, but that restriction endonuclease analysis is required for unambiguous identification of vaccine and field strains of ADV.     

猪繁殖与呼吸综合征病毒强弱毒株感染对仔猪免疫机能影响的差异

20日龄猪繁殖与呼吸综合征(PRRS)阴性健康仔猪滴鼻感染猪繁殖与呼吸综合征病毒(PRRSV) Hn-1/06强毒株和BJ-4弱毒株,于接种后0、5、11、18、30、40、50 d无菌采血,制备血清和分离白细胞,并在感染猪发病死亡或第50天后分别剖杀取各器官组织.经RT-PCR方法检测,强弱毒株在血清、白细胞和各组织器官内分布基本一致;经ELISA方法和免疫荧光抑制试验及IFA流式细胞术检测,强弱毒株感染均诱导机体产生抗N蛋白抗体,强毒株的抗N蛋白抗体产生早于弱毒株;强毒株感染未能诱导产生中和抗体,弱毒株感染后第30天诱导产生了较低水平的中和抗体,随后逐步升高;在整个感染过程中,强毒感染猪CD3+T淋巴细胞及CD4+和CD8+T淋巴细胞亚群均下降,CD4+/CD8+比值远远小于对照组,弱毒感染猪CD3+T淋巴细胞及CD4+和CD8+T淋巴细胞亚群先下降,40 d后逐渐恢复正常水平,CD4+/CD8+比值先下降,11 d后开始逐步上升,18 d后超过对照组,近50 d恢复到正常水平.结果说明,在强毒株感染过程中,细胞免疫被抑制,不能产生有效的体液免疫,导致病毒快速增殖复制;在弱毒株感染过程中,细胞免疫和体液免疫先被抑制,后免疫功能逐步恢复正常水平,使体内病毒进一步被清除.