Marek's disease virus infection in the brain: virus replication, cellular infiltration, and major histocompatibility complex antigen expression

Marek's disease virus (MDV) infection in the brain was studied chronologically after inoculating 3-week-old chickens of two genetic lines with two strains of serotype I MDV representing two pathotypes (v and vv+). Viral replication in the brain was strongly associated with the development of lesions. Three viral antigens (pp38, gB, and meq) were detected in the brain of infected chickens. Marked differences between v and vv+ pathotypes of MDV were identified for level of virus replication, time course of brain lesions, and expression of major histocompatibility complex (MHC) antigens. Two pathologic phenomena (inflammatory and proliferative) were detected in the brain of chickens inoculated with vv+MDV, but only inflammatory lesions were observed in those inoculated with vMDV. Inflammatory lesions, mainly composed of macrophages, CD4+ T cells, and CD8+ T cells, started at 6-10 days postinoculation (dpi) and were transient. Proliferative lesions, characterized by severe infiltrates of CD4+CD8- T cells (blasts), started at 19-26 dpi and persisted. Expression of MHC antigens in endothelial cells and infiltrating cells within the brain was influenced by MDV infection. Upregulation of MHC class II antigen occurred in all treatment groups, although it was more severe in those inoculated with vv+MDV. MHC class I antigen was downregulated only in those groups inoculated with vv+MDV. These results enhance our understanding of the nature and pattern of MDV infection in the brain and help to explain the neurovirulence associated with highly virulent MDV.     

Resistance to Marek's disease herpesvirus-induced lymphoma is multiphasic and dependent on host genotype

Genotype-dependent differences in Marek's disease (MD) susceptibility were identified using 14-day-old line N and 6(1) (resistant) and 151 and 7(2) (susceptible) inbred chickens infected with HPRS-16 MD virus (MDV). All line 72 chickens developed progressive MD. Line 15I had fluctuating MD-specific clinical signs and individuals recovered. A novel histologic scoring system enabled indices to be calculated for lymphocyte infiltration into nonlymphoid organs. All genotypes had increased mean lesion scores (MLSs) and mean total lesion scores after MDV infection. These differed quantitatively and qualitatively between the genotypes. Lines 6(1) and 7(2) had a similar MLS distribution in the cytolytic phase, although scores were greater in line 7(2). At the time lymphomas were visible in line 7(2), histologic lesions in line 6(1) were regressing. AV37+ cells were present in similar numbers in all genotypes in the cytolytic phase, suggesting that neoplastically transformed cells were present in all genotypes regardless of MD susceptibility. After the cytolytic phase, AV37+ cell numbers increased in lines 7(2) and 15I but decreased in lines 6(1) and N. In the cytolytic and latent phases, in all genotypes, most infiltrating cells were CD4+. After this time, line 7(2) and 15I lesions increased in size and most cells were CD4+; line 6(1) and N lesions decreased in size and most cells were CD8+. In all genotypes, AV37 immunostaining was weak in lesions with many CD8+ cells, suggesting that AV37 antigen expression or AV37+ cells were controlled by CD8+ cells. The rank order, determined by clinical signs and pathology, for MD susceptibility (highest to lowest) was 7(2) > 15I > 6(1) > N.     

Comparative analysis of Marek's disease virus (MDV) glycoprotein-, lytic antigen pp38- and transformation antigen Meq-encoding genes: association of meq mutations with MDVs of high virulence

Marek's disease (MD) is a highly contagious lymphoproliferative and demyelinating disorder of chickens. MD is caused by Marek's disease virus (MDV), a cell-associated, acute-transforming alphaherpesvirus. For three decades, losses to the poultry industry due to MD have been greatly limited through the use of live vaccines. MDV vaccine strains are comprised of antigenically related, apathogenic MDVs originally isolated from chickens (MDV-2), turkeys (herpesvirus of turkeys, HVT) or attenuated-oncogenic strains of MDV-1 (CVI-988). Since the inception of high-density poultry production and MD vaccination, there have been two discernible increases in the virulence of MDV field strains. Our objectives were to determine if common mutations in the major glycoprotein genes, a major lytic antigen phosphoprotein 38 (pp38) or a major latency/transformation antigen Meq (Marek's EcoRI-Q-encoded protein) were associated with enhanced MDV virulence. To address this, we cloned and sequenced the major surface glycoprotein genes (gB, gC, gD, gE, gH, gI, and gL) of five MDV strains that were representative of the virulent (v), very virulent (vv) and very virulent plus (vv+) pathotypes of MDV. We found no consistent mutations in these genes that correlated strictly with virulence level. The glycoprotein genes most similar among MDV-1, MDV-2 and HVT (gB and gC, approximately 81 and 75%, respectively) were among the most conserved across pathotype. We found mutations mapping to the putative signal cleavage site in the gL genes in four out of eleven vv+MDVs, but this mutation was also identified in one vvMDV (643P) indicating that it did not correlate with enhanced virulence. In further analysis of an additional 12 MDV strains, we found no gross polymorphism in any of the glycoprotein genes. Likewise, by PCR and RFLP analysis, we found no polymorphism at the locus encoding the pp38 gene, an early lytic-phase gene associated with MDV replication. In contrast, we found distinct mutations in the latency and transformation-associated Marek's EcoRI-Q-encoded protein, Meq. In examination of the DNA and deduced amino acid sequence of meq genes from 26 MDV strains (9 m/vMDV, 5 vvMDV and 12 vv+MDVs), we found distinct polymorphism and point mutations that appeared to correlate with virulence. Although a complex trait like MDV virulence is likely to be multigenic, these data describe the first sets of mutations that appear to correlate with MDV virulence. Our conclusion is that since Meq is expressed primarily in the latent/transforming phase of MDV infection, and is not encoded by MDV-2 or HVT vaccine viruses, the evolution of MDV virulence may be due to selection on MDV-host cell interactions during latency and may not be mediated by the immune selection against virus lytic antigens such as the surface glycoproteins.     

鸡马立克氏病活疫苗免疫效力比较试验

用ＨＶＴ冻干苗、ＨＶＴ细胞结合苗、ＣＶＩ９８８细胞结合苗、ＳＢ１＋ＦＣ１２６双价活疫苗、３０１Ｂ／１＋ＦＣ１２６双价活疫苗和Ｚ４＋ＦＣ１２６双价活疫苗等６种鸡马立克氏病（ＭＤ）疫苗免疫ＳＰＦ白来航鸡或普通伊莎鸡，用鸡马立克氏病病毒（ＭＤＶ）强毒ＧＡ株、京－１血毒以及鸡马立克氏病超强毒ｖｖＭＤＶ－Ｍｄ５毒株分别攻击进行免疫效力比较试验。试验表明，ＭＤ单价苗的免疫效力强弱顺序依次是ＣＶＩ９８８、ＨＶＴ细胞结合苗和ＨＶＴ冻干苗，这３种ＭＤ单价苗均能给免疫鸡群提供有效的免疫保护力。ＳＢ１＋ＦＣ１２６、Ｚ４＋ＦＣ１２６和３０１Ｂ／１＋ＦＣ１２６等３种ＭＤ双价苗免疫效力显著高于ＭＤ单价苗，均能给免疫鸡群提供较强的免疫保护力，并能有效地抵抗ｖｖＭＤＶ－Ｍｄ５毒株的致瘤作用。Ｚ４＋ＦＣ１２６和３０１Ｂ／１＋ＦＣ１２６ＭＤ双价苗免疫效力无显著差异     

Pathological and immunohistochemical studies of subclinical infection of chicken anemia virus in 4-week-old chickens

Subclinical infection of chicken anemia virus (CAV) at 4 to 6 weeks of age, after maternal antibodies have waned, is implicated in several field problems in broiler flocks. In order to understand the pathogenesis of subclinical infection with CAV, an immunopathological study of CAV-inoculated 4-week-old SPF chickens was performed. Sixty 4-week-old SPF chickens were equally divided into CAV and control groups. The CAV group was inoculated intramuscularly with the MSB1-TK5803 strain of CAV. Neither mortality nor anemia was detected in the CAV and control groups. In the CAV group, no signs were observed, except that some chickens were grossly smaller compared with the control group. Sporadic thymus lobes appeared to be reddening and atrophied. Within the first two weeks p.i. of CAV, there was a mild to moderate depletion of lymphocytes in the thymus cortex and spleen in some chickens. Moreover, lymphoid depletion of the bursa of Fabricius, proventriculus and cecal tonsils was observed. Hyperplastic lymphoid foci were observed in the liver, lungs, kidneys and heart at the 4th week p.i. of CAV. Immunohistochemically, a moderate lymphoid depletion of CD4(+)and CD8(+) T cells in the thymus cortex and spleen was observed in some chickens within two weeks p.i. of CAV. CAV inclusions and antigens were detected infrequently in the thymus cortex and spleen. It could be concluded that the immunosuppression in subclinical infection with CAV occurs as a result of reduction of cellular immunity.     

Relationship between tumour development and detection of Marek's disease virus in the feather follicular epithelium of older chickens

To demonstrate the relationship between tumour development and virus replication, eight specific-pathogen-free pullets of line P2 (Group P; 14 weeks old) and five adult chickens (Group A; 96 weeks old) were inoculated with virulent Marek's disease virus (vMDV). Five chickens of Group P died or were euthanised due to moribund condition following the development of neoplastic lesions between days 53 and 91. On histopathological examination, these lesions were characterised by the proliferation of lymphoid cells of variable size. On analysis by polymerase chain reaction (PCR), the MDV meq gene was detected in Group P from day 21, and it was continuously identified in five chickens until they died or were euthanised. Abnormal signs and histopathological changes were not observed in chickens of Group A. The MDV meq gene was temporarily detected in some chickens of Group A, but it remained almost undetectable throughout the experimental period. In older chickens inoculated with vMDV, the onset of MD lymphoma development tended to be delayed as compared with the young chicks. The relationship between MD lymphoma development and virus replication in older chickens has been suggested. Our data might indicate the underlying existence of an age-related resistance to vMDV challenge.     

Isolation of very virulent Marek''s disease viruses from vaccinated chickens in Australia

Very virulent Marek's disease viruses (vvMDV), defined as isolates against which the herpesvirus of turkey (HVT) vaccine provide poor protection, have been isolated from poultry flocks in both the United States and Europe. Twenty-one samples from vaccinated Australian flocks, experiencing problems with excessive Marek's disease (MD), were tested for the presence of transmissible MD viruses (MDV). Of the 16 samples which contained a transmissible agent, 14 were pathogenic in chickens, based on the development of MD lesions or depression of the bursa/body weight ratio. Of the pathogenic isolates which have been successfully typed 10 were serotype 1, and one was serotype 2 MDV. Pathogenicity of isolates varied. Several isolates caused tumours in 20-30% of both vaccinated and unvaccinated chickens. Two isolates, MPF6 and MPF23, caused tumours in more than 50% of chickens. When MPF6 and MPF23 were tested in vaccine trials bivalent vaccine gave no better protection against development of MD lesions than a monovalent vaccine. Isolate MPF23 was so pathogenic that lesions were produced in all chickens, regardless of the vaccine protocol used. Therefore vvMDV have been isolated in Australia, and unlike the vaccines tested overseas, bivalent Australian vaccines do not appear to provide greater protection against these vvMDV.     

Protective efficacy of Marek's disease virus (MDV) CVI-988 CEF65 clone C against challenge infection with three very virulent MDV strains

Comparative 50% protective dose (PD50) assays were performed using a plaque-purified preparation of Marek's disease virus (MDV) strain CVI-988 at the 65th chicken embryo fibroblast (CEF) passage level (MDV CVI-988 CEF65 clone C) and three commercial MD vaccines: herpesvirus of turkeys (HVT) FC126, MDV CVI-988 CEF35, and a bivalent vaccine composed of HVT FC126 and MDV SB-1. In addition, comparative PD50 assays were performed in groups of chickens with maternal antibody to each of the three vaccines. Three representatives of the newly emerged biovariant very virulent (vv) MDV strains-RB/1B, Tun, and Md5-were employed as challenge virus. The experiments made feasible the differentiation between virulent MDV and vvMDV strains, within serotype 1. Vaccination with CVI-988 clone C vaccine resulted in PD50 estimates of about 5 plaque-forming units (PFUs) against challenge infection with each of the three vvMDV strains. The PD50 estimate of CVI-988 clone C vaccine was 12-fold below the PD50 of HVT FC126. The protective synergism of bivalent vaccine, composed of HVT and SB-1, was confirmed by groups given the lowest vaccine doses. The bivalent vaccine, however, resulted in incomplete protection in groups given the highest vaccine doses. Homologous maternal antibodies to serotype 1 caused a fivefold increase in the PD50 estimate of CVI-988 clone C. Heterologous maternal antibodies against HVT did not interfere with efficacy of CVI-988 clone C vaccination. However, the combination of maternal antibodies against both HVT and SB-1 (serotypes 2 and 3) showed a strong adverse effect on CVI-988 clone C vaccine.(ABSTRACT TRUNCATED AT 250 WORDS)     

健康中国恒河猴各淋巴组织中T淋巴细胞表型及分布

试验旨在明确T淋巴细胞在中国恒河猴各组织中的表型与分布,为疾病模型研究提供基础数据。取外周血、腹股沟淋巴结、肠系膜淋巴结及肠道组织,从中分离出淋巴细胞。使用流式细胞术检测分析各种表型的淋巴细胞在组织间的分布。结果表明,淋巴结中CD4⁺ /CD8⁺ T细胞比值高于外周血,肠道固有层中最低,三者差异显著。记忆性T细胞在外周血和肠道固有层T细胞中比重较大,而淋巴结中主要为幼稚T细胞。CD4⁺ T细胞中中心记忆T细胞Tcm为主要亚群,而CD8⁺ T细胞主要为效应记忆细胞Tem。外周血与肠道固有层中增殖T细胞比例相当,而淋巴结中T细胞增殖水平相对较低。各组织中CXCR4受体表达量普遍高于CCR5受体,其中肠道固有层CCR5受体表达水平最高。值得注意的是,有一小群表型CD3⁺ CD4⁺ CD8low的细胞仅在肠道固有层中存在,经分析其功能活性应高于肠道CD4单阳性T细胞。因此,测定了健康中国恒河猴各表型T淋巴细胞在多种淋巴组织中的基础数值,为相关模型研究奠定基础。     

Detection of the meq gene in the T cell subsets from chickens infected with Marek's disease virus serotype 1

The meq gene was thought to be only detected in Marek's disease virus serotype 1 (MDV 1) including a very virulent strain, Md5, while L-meq, in which a 180-bp sequence is inserted into the meq open reading frame, is found in other strains of MDV 1, such as CVI 988/R6. However, both meq and L-meq were previously detected by PCR in chickens infected with MDV 1, suggesting that MDV 1 may consists of at least two subpopulations, one with meq, the other with L-meq. To further analyze these subpopulations, we analyzed the time course changes in distribution of these subpopulations among T cell subsets from chickens infected with MDV 1. Both meq and L-meq were detected in CD4+ and CD8+ T cells infected with strain Md5 or CVI 988/R6. The shift in MDV subpopulations from one displaying meq to the other displaying L-meq and/or the conversion from meq to L-meq occurred mainly in the CD8+ T cell subset from Md5-infected chickens. PCR products corresponding to L-meq rather than meq were frequently amplified from the CD8+ T cell subset from CVI 988/R 6 -infected chickens. These results suggest that a dominant subpopulation of MDV 1 changes depending on the T cell subsets, and that L-meq is dominantly present in the CD8+ T cells which play a role in the clearance of pathogenic agents.     

Canine CD4(+)CD8(+) double positive T cells in peripheral blood have features of activated T cells

In dogs a CD4(+)CD8(+) double positive T cell subpopulation exists that has not been phenotypically defined yet. We demonstrate that canine CD4(+)CD8(+) T cells are mature CD1a(-) and TCRαβ(+) T cells. To analyse the activation potential of CD4(+)CD8(+) T cells, PBMC from dogs vaccinated against canine distemper virus (CDV) were re-stimulated with CDV. Upon antigen-specific stimulation, the CD4(+)CD8(+) T cell fraction increases and consists nearly exclusively of proliferated cells. Similarly, other features of activated effector/memory T cells such as up-regulation of CD25 and MHC-II as well as down-regulation of CD62L (L-selectin) were observed in CD4(+)CD8(+) T cells after stimulation. Canine CD4(+)CD8(+) T cells are less abundant, but more heterogeneous than porcine ones, comprising a small proportion expressing the β chain of CD8 in addition to the CD8α chain, like human CD4(+)CD8(+) T cells. In summary, this analysis provides the basis for functional characterisation of the in vivo relevance of CD4(+)CD8(+) T cells in T-cell mediated immunity.     

Marek’s disease virus may interfere with T cell immunity by TLR3 signals

Marek’s disease virus (MDV) is a highly oncogenic alpha-herpesvirus that causes T cell immune suppression and malignant lymphomas in chickens. Toll-like receptor (TLR) plays a dominant role in antiviral T cell immunity. However, it is unclear whether MDV induced T cell immunity is associated with TLR-mediated immunity. In this study, the expression of 28 host genes that are involved in TLR-mediated immunity and MHC-medicated T cell immunity was evaluated in chicken thymus at 7, 14, 21 and 28 days post-infection (dpi). Our results demonstrated that 24 host immune-related genes were upregulated during MDV infection at 7 dpi; however, the expression of most of these genes decreased at 21 and 28 dpi. Notably, a positive correlation was found between the down-regulation of CD4, CD8 and TLR3 signals but not the MyD88-dependent TLR pathway. The present study expanded our knowledge of host immune responses against MDV infection and our results might provide a clue that MDV may interfere with T cell immune response through TLR3 signals.     

鸡马立克病研究进展

鸡马立克病是由马立克病病毒引起的一种淋巴细胞增生性传染病,通常以外周神经和包括虹膜和皮肤在内的其他各种器官和组织的单核细胞浸润为特征.目前,仍然严重威胁着养禽业的发展,疫苗虽然可以预防马立克病的发生,但免疫失败时有发生,常常导致本病的局部暴发.论文对该病的病原、流行病学、临床症状、病理变化、发病机理、诊断及防控等方面进行了综述.     

不同MD免疫抗性鸡羽髓中疫苗毒与超强毒的复制动力学及相关性研究

为研究具有不同抗性的马立克氏病(MD)疫苗免疫鸡羽髓后,疫苗毒和超强毒(vvMDV)的复制动力学及两种病毒载量的相关性,本实验对经火鸡疱疹病毒(HVT)FC126疫苗株免疫1周后(1wpv),攻击vvMDV Md5株G3系和G7系鸡羽髓中的HVT和vvMDV载量进行定量检测及相关性分析。结果显示,G3系和G7系鸡群羽髓中的vvMDV载量始终高于疫苗毒。其中,G3系鸡群在免疫和攻毒后的相同时间内,疫苗毒与vvMDV载量的消长规律基本一致,均在感染后第4周(4wpi)出现峰值,6wpi降至最低水平,两种病毒载量多表现为正相关,6wpv～8wpv为持续显著正相关;G7系的两种病毒的复制动力学存在差异:vvMDV载量从攻毒后第6周呈增长趋势,而疫苗毒在4wpv出现峰值后迅速下降,两种病毒载量多表现为负相关。本研究表明,免疫遗传基因在对病毒的抵抗中起主要作用,为MDV的感染机制和疫苗免疫机理的研究提供实验依据。     

Immune mechanisms in Marek's disease.

Resistance to progressive tumor development in MD is either naturally inherited or can be induced by vaccination with apathogenic or attenuated MDV or with HVT. Studies on the effects of immunosuppression on resistance have shown that natural and vaccine induced resistance may be mediated through immune responses. Cell-mediated immune responses rather than humoral responses appear to be of principal importance. The antigen(s) against which protective cell-mediated immunity is elicited are not yet clearly delineated. Both virus-related and tumor antigens may be involved. Progress in the understanding of cell-mediated immunity in MD has been slow because of lack of reproducible in vitro tests to measure this response in infected chickens. The development of lymphoblastoid cell lines from MD lymphomas, however, has enabled the development of an in vitro cytotoxicity test. In this test, which utilizes MSB-1 cells as the target cells, a specific cell-mediated immune response, presumably against the tumor antigen, MATSA, was detected in chickens infected with MDV. Further studies using similar in vitro tests will facilitate a better understanding of the role cell-mediated immune responses might play in development of MD.     

香菇多糖和黄芪多糖对马立克氏病强毒感染雏鸡白细胞介素2活性和淋巴细胞增殖反应的影响

１日龄ＡＡ肉用雏鸡以马立克氏病强毒（ｖＭＤＶ）人工感染后,马立克氏病（ＭＤ）发病率３３．７５％,死亡率１１．２５％。同健康雏鸡相比,ＩＬ－２诱生活性和Ｔ淋巴细胞增殖反应降低（Ｐ＞０．０５）和显著降低（Ｐ＜０．０５）。ｖＭＤＶ感染雏鸡注射香菇多糖和黄芪多糖,ＭＤ发病率分别为２０％、１７．５％,死亡率分别为７．５％、５％。同感染组相比,感染／香菇组和感染／黄芪组的ＩＬ－２诱生活性和Ｔ淋巴细胞增殖反应均升高（Ｐ＞０．０５）和显著升高（Ｐ＜０．０５）。     

Characterization of efferent lymph cells and their function following immunization of cattle with an allogenic Theileria annulata infected cell line

Immunization of cattle with in vitro propagated bovine mononuclear cells infected with Theileria annulata induces a protective immune response. Activation and effector function of T cells exiting the lymph node draining the site of cell line immunization were investigated to understand the mechanisms involved in the generation of immunity. Immunized animals exhibited a biphasic immune response in efferent lymph as well as peripheral blood. The first phase corresponded to allogenic responses against MHC antigens of the immunizing cell line and the second was associated with parasite specific responses. An increase in the output of CD2(+) cells and MHC class II(+) cells in efferent lymph was observed after cell line immunization with a corresponding decrease in WC1(+) cells. Although the percentage of CD4(+) T cells did not change significantly over the course of the experiment, they became activated. Both CD25 and MHC class II expressing CD4(+) T cells were detected from day 7 onwards, peaking around day 13. Efferent lymph leukocytes (ELL) exhibited sustained responses to IL-2 in vitro following cell line immunization. Antigen specific proliferation was also detected first to the immunizing cell line and then to parasite antigens. The two peaks of CD2(+) cells were observed, which corresponded to similar peaks of CD8(+) cells. The increase in CD8(+) cells was more pronounced during the second parasite specific phase than the first allogenic phase. Activated CD8(+) T cells mainly expressed MHC class II and some expressed CD25. Significantly the peak of activated CD4(+) T cells preceded the peak of activated CD8(+) T cells, highlighting the role of T. annulata specific CD4(+) T cells in inducing parasite specific CD8(+) cytotoxic responses. A biphasic cytotoxic response also appeared in efferent lymph and peripheral blood, the first directed against MHC antigens of the immunizing cell line followed by MHC class I restricted parasite specific cytotoxicity. The cytotoxic responses in efferent lymph appeared earlier than peripheral blood, suggesting that activated CD8(+) cells exiting the draining lymph node following immunization with T. annulata infected schizonts play an important role in the development of protective immune responses.     

鸡贫血病灭活疫苗免疫后雏鸡免疫状况研究

应用鸡传染性贫血病灭活疫苗免疫雏鸡后,１０、２０、３５、４５天检测了空白对照组、免疫组的外周血液、胸腺、脾脏和法氏囊内ＣＤ３＋、ＣＤ４＋、ＣＤ８＋、γδＴ细胞亚群、ＩｇＧ阳性细胞的变化;并且在３５天、４５天检测免疫攻毒组和攻毒组上述细胞免疫和体液免疫指标的变化。结果显示,应用贫血病灭活疫苗后免疫组雏鸡的Ｔ细胞亚群的ＣＤ４／ＣＤ８比值出现明显降低,ＩｇＧ阳性细胞有升高变化;免疫攻毒组雏鸡状态明显好于攻毒组。研究表明,鸡传染性贫血病疫苗可以激发机体体液免疫反应,并在一定程度上诱导ＣＴＬ活化,对ＣＡＶ攻击产生足够的免疫保护。     

商品肉鸡群中MDV、REV、CAV和ARV多重感染的检测

从山东省东营、日照、潍坊、聊城等地区自然发病和临床健康AA商品肉鸡群中分别采集脏器样品,用特异性核酸探针对样品进行马立克氏病病毒（Marek’s disease virus,MDV）、网状内皮组织增生症病毒（Reticuloendotheliosis virus,REV）、鸡传染性贫血病病毒（Chicken anemia virus,CAV）和禽呼肠孤病毒（Avian reoviruses,ARV）检测。结果显示,自然发病AA商品肉鸡群中MDV、REV、CAV和ARV的检出率均较高,分别为69．30％、57．46％、63．60％和67．11％;临床健康AA商品肉鸡群中MDV、REV、CAV的检出率分别为36．96％、43．48％和30．42％,且自然发病和健康鸡群中均存在不同病毒组合的多重感染,感染率分别为85．96％和43．46％。用x2检验进行分析发现,自然发病商品肉鸡群与临床健康商品肉鸡群中MDV、CAV、MDV＋REV、REV＋CAV的检出率和未检出的比例差异极显著（P〈0．01）;REV、MDV＋CAV检出率差异显著（P〈0．05）。对自然发病商品肉鸡的肝脏、脾脏、法氏囊中4种病毒检出率进行X2检验分析发现,MDV在脾脏中检出率显著高于肝脏和法氏囊;REV在法氏囊中检出率显著高于肝脏和脾脏,而CAV和ARV分别在脾脏和肝脏中检出率较高。结果表明,多种免疫抑制性病毒的共感染已普遍存在,是目前AA商品肉鸡易发病且生长缓慢的重要流行病学因素之一。     

CD8(+) T cell knockout mice are less susceptible to Cowdria ruminantium infection than athymic, CD4(+) T cell knockout, and normal C57BL/6 mice

The role of T cells in immunity to Cowdria ruminantium was investigated by studying the responses to infection of normal, athymic, CD4(+) T cell knock out (KO) and CD8(+) T cell KO C57BL/6 mice. Normal C57BL/6 mice could be immunized by infection and treatment, and immunity was adoptively transferable from immune to naive mice by splenocytes. Following infection, athymic mice died sooner than normal mice (P=0.0017), and could not be immunized by infection and treatment. CD4(+) T cell KO mice were as susceptible to infection as normal mice and could be immunized by infection and treatment. In contrast, CD8(+) T cell KO mice were less susceptible than normal and CD4(+) T cell KO mice and 43% self-cured, while those that died did so after a prolonged incubation period. Antibody responses to C. ruminantium were CD4(+) T cell dependent, because responses were detected in immune normal and CD8(+) T cell KO mice but not in immune CD4(+) KO mice (P=0.005). Since CD8(+) T cell KO mice were less susceptible to infection, and since CD4(+) T cell KO mice could be immunized, it can be concluded that immunity to C. ruminantium can be mediated by both CD4(+) and CD8(+) T cells.