Pullorum Disease: Evolution of the Eradication Strategy

The history of pullorum disease is closely intertwined with the history of avian health research and that of the poultry industry. The seriousness of the disease galvanized the attention and brought together, for the first time, the pioneers of poultry health research to work cooperatively on different aspects of the disease. Control of the disease made it possible for intensive poultry production to develop as the basis for the modern poultry industry. During the early 1900s, bacillary white diarrhea (BWD) was a devastating disease of young chickens threatening the developing poultry industry. Dr. Leo F. Rettger isolated and described the bacterial pathogen, Salmonella enterica serotype Pullorum, for the first time in 1900. BWD was renamed pullorum disease in 1929. In subsequent years, Rettger and coworkers were able to reproduce the disease and fulfill Koch's postulates. Rettger et al. also showed that Salmonella Pullorum was vertically transmitted, which was the first time that a pathogen was shown to be vertically transmitted. The development of serologic tests was of crucial importance because it led to the development of effective eradication methods to identify carrier birds and to exclude these birds from the breeder flocks. The negative impact of pullorum disease on the poultry industry ultimately was one of the major reasons that the National Poultry Improvement Plan (NPIP) was developed by scientists, the poultry industry, and the United States Department of Agriculture (USDA). Needless to say, the work of the pioneering researchers formed the basis for the control of the disease. The NPIP started in 1935, with 34 states participating in testing 4 million birds representing 58.2% of the birds hatched. The program rapidly expanded to 47 states by 1948 and tested more than 30 million birds. In 1967, all commercial chicken hatcheries participating in the NPIP were 100% free of pullorum and typhoid disease caused by Salmonella enterica serotype Gallinarum. This historical overview of pullorum disease describes in some detail the progress made, especially during the early years, toward controlling this disease using methodologies that were often very basic but nonetheless effective. One has to admire the ingenuity and persistence of the early researchers leading to their achievements considering the research tools that were available at the time.

Virus-Induced Immunosuppression in Chickens

A healthy immune system is a cornerstone for poultry production. Any factor diminishing the immune responses will affect production parameters and increase cost. There are numerous factors, infectious and noninfectious, causing immunosuppression (IS) in chickens. This paper reviews the three viral diseases that most commonly induce IS or subclinical IS in chickens: Marek's disease virus (MDV), chicken infectious anemia virus (CIAV), and infectious bursal disease virus (IBDV), as well as the interactions among them. MDV-induced IS (MDV-IS) affects both humoral and cellular immune responses. It is very complex, poorly understood, and in many cases underdiagnosed. Vaccination protects against some but not all aspects of MDV-IS. CIAV induces apoptosis of the hemocytoblasts resulting in anemia, hemorrhages, and increased susceptibility to bacterial infections. It also causes apoptosis of thymocytes and dividing T lymphocytes, affecting T helper functions, which are essential for antibody production and cytotoxic T lymphocyte (CTL) functions. Control of CIAV is based on vaccination of breeders and maternal antibodies (MAbs). However, subclinical IS can occur after MAbs wane. IBDV infection affects the innate immune responses during virus replication and humoral immune responses as a consequence of the destruction of B-cell populations. Vaccines with various levels of attenuation are used to control IBDV. Interactions with MAbs and residual virulence of the vaccines need to be considered when designing vaccination plans. The interaction between IBDV, CIAV, and MDV is critical although underestimated in many cases. A proper control of IBDV is a must to have proper humoral immune responses needed to control CIAV. Equally, long-term control of MDV is not possible if chickens are coinfected with CIAV, as CIAV jeopardizes CTL functions critical for MDV control.

Role of chicken astrovirus as a causative agent of gout in commercial broilers in India

Several outbreaks of gout were reported in commercial broilers in India during 2011 and 2012, causing up to 40% mortality in the birds. Gross and histopathological observations confirmed gout. Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) analysis from kidney samples of gout-affected birds indicated the presence of chicken astrovirus (CAstV) in 41.7% of cases and a mixed infection of CAstV and avian nephritis virus (ANV) in 36.4% of cases. CAstV isolated from gout-affected kidneys by inoculating embryonated specific pathogen free (SPF) eggs showed dwarfing in embryos and a cytopathic effect in chicken embryo kidney cells. Inoculation of 1-day-old SPF and broiler chicks with CAstVs caused gout and mortality between 4 and 10 days post inoculation. Virus isolation and qRT-PCR analysis showed the presence of only CAstV in inoculated chicks. Sequence analysis of capsid genes indicated a major group of Indian CAstVs that displayed 92.0 to 99.2% intergroup amino acid identity and 83.9 to 90.4% identity with subgroup Bi CAstVs of UK origin. We designated this group Indian Bi. Analysis of the partial polymerase amino acid sequences of our isolates indicated two groups of CAstVs (Indian 1 and 2) that displayed 90.2 to 95.5% amino acid identity between them. We thus report for the first time that, in addition to infectious bronchitis virus and ANV, CAstVs are a causative agent of gout.

Characterization of the host response in systemic isosporosis (atoxoplasmosis) in a colony of captive American goldfinches (Spinus tristis) and house sparrows (Passer domesticus)

Systemic isosporosis, also known as atoxoplasmosis, is a common parasitic disease of passerines. Infection is thought to be endemic in wild birds with fulminant, fatal disease occurring under the influence of stress, concurrent infections, or immunosuppression. Here, we describe the histologic and immunohistochemical characteristics of the cellular infiltrate occurring in captive colonies of American goldfinches and house sparrows. Necropsies were performed on 9 birds, and histologic examination was performed on the intestines of 7 additional birds. Lesions were most severe in the proximal small intestines. Histologically, the changes ranged from variably intense infiltrates of lymphocytes that filled the lamina propria to sheets of large, atypical cells that expanded and obliterated normal mucosal epithelium and invaded through the wall of the intestine and into the ceolomic cavity. Both the smaller lymphocytes and large atypical cells were immunoreactive for CD3. Intracellular parasites consistent with Isospora were detected in the large atypical cells, but they were more easily detectable in the more differentiated lymphocytes. Polymerase chain reaction and virus isolation performed on tissues from 7 birds were negative for retroviruses and herpesvirus. The immunohistochemical results of this study and the destructive nature of the cellular infiltrate suggest that the lesion represents T-cell lymphoma. In birds, lymphomas are most often associated with herpes and retroviruses; the absence of these viruses suggests that the parasite initiated neoplastic transformation. Though much work needs to be done to prove the transformative nature of the lesions, these preliminary results suggest that passerine birds may be susceptible to parasite-associated lymphomas.

Common garden experiment reveals pathogen isolate but no host genetic diversity effect on the dynamics of an emerging wildlife disease

Host genetic diversity can mediate pathogen resistance within and among populations. Here we test whether the lower prevalence of Mycoplasmal conjunctivitis in native North American house finch populations results from greater resistance to the causative agent, Mycoplasma gallisepticum (MG), than introduced, recently-bottlenecked populations that lack genetic diversity. In a common garden experiment, we challenged wild-caught western (native) and eastern (introduced) North American finches with a representative eastern or western MG isolate. Although introduced finches in our study had lower neutral genetic diversity than native finches, we found no support for a population-level genetic diversity effect on host resistance. Instead we detected strong support for isolate differences: the MG isolate circulating in western house finch populations produced lower virulence, but higher pathogen loads, in both native and introduced hosts. Our results indicate that contemporary differences in host genetic diversity likely do not explain the lower conjunctivitis prevalence in native house finches, but isolate-level differences in virulence may play an important role.

Chicken anemia virus

Chicken anemia virus (CAV), the only member of the genus Gyrovirus of the Circoviridae, is a ubiquitous pathogen of chickens and has a worldwide distribution. CAV shares some similarities with Torque teno virus (TTV) and Torque teno mini virus (TTMV) such as coding for a protein inducing apoptosis and a protein with a dual-specificity phosphatase. In contrast to TTV, the genome of CAV is highly conserved. Another important difference is that CAV can be isolated in cell culture. CAV produces a single polycistronic messenger RNA (mRNA), which is translated into three proteins. The promoter-enhancer region has four direct repeats resembling estrogen response elements. Transcription is enhanced by estrogen and repressed by at least two other transcription factors, one of which is COUP-TF1. A remarkable feature of CAV is that the virus can remain latent in gonadal tissues in the presence or absence of virus-neutralizing antibodies. In contrast to TTV, CAV can cause clinical disease and subclinical immunosuppression especially affecting CD8+ T lymphocytes. Clinical disease is associated with infection in newly hatched chicks lacking maternal antibodies or older chickens with a compromised humoral immune response.

Pathogenesis of rotavirus infection in turkey poults

The pathogenesis of rotavirus infection was examined after experimental infection of conventional and specific-pathogen-free (SPF) turkey poults. In six experiments birds were exposed to turkey rotavirus isolates Tu-1 or TU-2 or the chicken isolate Ch-1 at 7, 10 or 42 days of age. Poults were examined between 1 and 24 days post-infection (dpi) for diarrhoea, gross and histopathologic lesions, virus excretion in the intestinal tract, viral antigen in intestinal epithelial cells, and the development of serum antibodies. Between 2 and 5 dpi watery droppings were observed in conjunction with remarkable paleness of the intestinal tract which was grossly observable. Maximum viral replication occurred between 2 and 5 dpi, during which period viral antigen could be demonstrated in the epithelial cells of the duodenum, jejunum, ileum and colon. Sporadically, virus antigen-positive cells were seen in the cecum. As early as 4 to 5 dpi rotavirus antibodies could be detected by indirect immunofluorescence assays. Remarkable leukocyte infiltration of the lamina propria, vacuolation of the epithelial cells and scalloping of the villous surface at the tips were observed in the intestine of infected birds. Infection with rotavirus caused a significant impairment at 2 and 4 dpi of absorption of D-xylose from the intestinal tract.

Characterisation of two highly oncogenic strains of Marek's disease virus

The RB-1B and ALA-8 strains of Marek's disease (MD) virus, which were isolated from chickens with MD and which had been vaccinated with the herpesvirus of turkeys (HVT), were evaluated for their oncogenic potential in genetically susceptible (P-line) and resistant (N-line, PDRC) chickens. RB-1B and ALA-8 were both highly oncogenic, causing a high incidence of MD in both susceptible and resistant birds. Vaccination of P-line birds with SB-1 or HVT did not protect satisfactorily against RB-1B. However, a bivalent vaccine consisting of SB-1 and HVT enhanced protection significantly. HVT alone, and the bivalent vaccine, protected PDRC and N-line chickens well against RB-1B, but SB-1 was less protective in PDRC birds. HVT protected equally well against challenge with ALA-8 and the standard JM-10 strain. Differences in the pathogenesis of viral infection could not be detected among ALA-8, RB-1B and JM-10 between 4-7 days post-infection (d.p.i.). However, after d.p.i. 12 RB-1B caused significantly higher levels of viral internal antigen and virus isolation rates than did JM-10 in the same genetic strain. Prior vaccination prevented the expression of ALA-8 at 5 and 20 d.p.i., but not that of RB-1B. Pathogenetic events such as expression of VIA or level of virus infection appeared to be directly related to the level of protection observed in challenged birds.

Vaccination of village chickens in The Gambia against Newcastle disease using the heat-resistant, food-pelleted V4 vaccine

The Australian non-pathogenic, heat-resistant V4 strain of Newcastle disease virus (NDV) in food-pellet form was used on a single occasion to vaccinate village poultry in The Gambia. The response of the chickens to the vaccine virus was monitored with the haemagglutination inhibition (HI) test. Pre-vaccination HI tests showed that the majority of chickens tested did not have antibodies to NDV. At 4 and 12 weeks post-vaccination, vaccinated chickens showed 30 and 48% seroconversion, respectively. The HI titres were indicative of protection, but challenge experiments were not undertaken. Only a low percentage of the control groups were antibody positive at these times.

Intestinal IgA response and immunity to rotavirus infection in normal and antibody-deficient chickens

Rotavirus inoculation by oesophageal cannulation resulted in subclinical infection without decreasing intestinal D-xylose absorption in both intact and embryonally bursectomised, antibody-deficient (EBx) 8-week-old specific-pathogen-free chickens. In intact chickens, rotavirus-specific IgM, IgG and IgA responses were detected in serum, while the intestinal antibody response consisted almost entirely of IgA Serum IgG and intestinal IgA levels were increased for at least 70 days following a single inoculation with the virus. Intact chickens recovered from a primary rotavirus infection between 4 and 14 days post inoculation (dpi) and developed resistance to homotypic challenge between 14 and 28 dpi. These responses were only slightly delayed in EBx birds, which recovered from primary infection between 8 and 28 dpi and developed resistance between 14 and 42 dpi. This suggested that the intestinal IgA response in chickens participated in both recovery from and resistance to rotavirus infection, but that it was not the only mediator of recovery and resistance.

The contribution of feathers in the spread of chicken anemia virus

Chicken anemia virus (CAV) spreads vertically and horizontally, however, the process is mostly still obscure. To further clarify the horizontal CAV spread, we examined the contribution of feathers. We demonstrated that CAV could be amplified from DNA purified from feather shafts of experimentally infected chicks, and the process efficacy was evaluated by comparing the amplification of DNA purified from feather shafts and lymphoid organs of CAV-experimentally infected chicks. DNA from feathers was found as an efficient source for CAV detection. Further, to substantiate whether CAV reaches the feather shafts passively via the blood, or intrinsically, causing histopathological changes, the feather follicle tissues were examined for CAV-induced lesions. Specific histological changes were found, however, immunohistochemistry failed to detect viral proteins. To determine whether the feather shafts are a source of infective virus, they were homogenized and used to infect 1-day-old chicks via the mucosal entries (eyes, nose and oropharynx). That infection mode simulates the natural route of horizontal infection in commercial poultry houses. We demonstrated the CAV-infection by serology, virology and pathology, showing that feather shafts carry infectious CAV either on their surface or within their feather pulp, and concluded that feathers contribute to the horizontal CAV dissemination.

Animal vaccination and the evolution of viral pathogens

Despite reducing disease, vaccination rarely protects against infection and many pathogens persist within vaccinated animal populations. Circulation of viral pathogens within vaccinated populations may favour the development of vaccine resistance with implications for the evolution of virus pathogenicity and the emergence of variant viruses. The high rate of mutations during replication of ribonucleic acid (RNA) viruses is conducive to the development of escape mutants. In vaccinated cattle, unusual mutations have been found in the major antigenic site of foot and mouth disease virus, which is also involved in receptor recognition. Likewise, atypical changes have been detected in the immunodominant region of bovine respiratory syncytial virus. Large deoxyribonucleic acid (DNA) viruses are able to recombine, generating new genotypes, as shown by the potential of glycoprotein E-negative vaccine strains of bovine herpesvirus-1 to recombine with wild-type strains. Marek's disease virus is often quoted as an example of vaccine-induced change in pathogenicity. The reasons for this increase in virulence have not been elucidated and possible explanations are discussed.

Classification of Marek's disease viruses according to pathotype: philosophy and methodology

The concept of pathotype in Marek's disease (MD) probably dates from the recognition of a more virulent form of the disease in the late 1950s (Benton & Cover, 1957). Distinctions between MD virus strains were further expanded with the description of the vv pathotype in the early 1980s and of the vv+ pathotype in the 1990s. Pathotype designations reflect important biological properties that correlate with the break-through of vaccinal immunity in the field. However, pathotyping methods applied by various laboratories have not been uniform, preventing critical comparison of results. Better uniformity of pathotyping procedures is desirable.The Avian Disease and Oncology Laboratory (ADOL) method is based on induction of lymphoproliferative lesions in vaccinated chickens. This method has been used to pathotype more than 45 isolates and is the basis for the current pathotype classification of MD virus strains. Its limitations include requirements for a specific type of chickens (15x7 ab+), large numbers of animals, and a statistical method to compare lesion responses to those of JM/102W and Md5 control strains. Because of these limitations, it has not been and is not likely to be used in other laboratories. Comparability in pathotyping can be improved by the comparison of field isolates with standard prototype strains such as JM/102W, Md5 and 648A (American Type Culture Collection) or their equivalents. Data may be generated by different in vivo procedures that measure tumour induction, neurological disease (both neoplastic and non-neoplastic lesions), or solely non-neoplastic criteria (such as lymphoid organ weights or virus replication). Methods based on neoplastic criteria, especially when generated in MD-immunized chickens, will probably correlate most closely with that of the ADOL method and be most relevant to evolution of MD virus in the field. Based on data from several trials, a modification of the ADOL method that utilizes fewer chickens and can be conducted with commercial specific pathogen free strains is proposed. The modified method is based on "best fit" comparisons with prototype strains, and is expected to provide results generally comparable with the original method. A variety of other alternative criteria (see earlier) are also evaluated both for primary pathotyping and as adjuncts to other pathotyping methods. Advantages and disadvantages of alternative methods are presented.

Isolation of Marek's disease virus: revisited

Splenocytes from chickens infected with low-passage stocks of Marek's disease virus (MDV) RB-1B, a very virulent (vv) strain and vv+ RK-1 were used to compare the efficacy of chick kidney cells (CKC), chicken embryo fibroblasts (CEF) and chicken embryo kidney cells (CEKC) for virus isolation. CKC were superior to CEF and CEKC. MDV foci were present at 4 days post infection in CKC but not until 6 days post infection in CEF or CEKC. Virus yield was higher in CKC than in CEF or CEKC at 6 days post infection. Passage of RB-1B in CKC yielded a significantly higher virus increase than with CEF or CEKC. The same was true for RK-1 comparing CKC with CEKC. Interestingly, RK-1-infected CEF were negative or had very low number of foci in passage 1, but virus yield increased 500-fold to 600-fold on passage in CKC, CEF, and CEKC. Recommendations on procedures for successful virus isolation are provided.

Detection of chicken anemia virus in the gonads and in the progeny of broiler breeder hens with high neutralizing antibody titers

Previous evidence for the presence of chicken anemia virus (CAV) in the gonads of immune specific-pathogen-free chickens raised the question whether this occurs also in commercial breeders. The presence of CAV was investigated by nested PCR in the gonads and spleens of hens from two 55- and 59-week-old, CAV-vaccinated (flocks 2 and 3), and two 48- and 31-week-old non-vaccinated broiler breeder flocks (flocks 1 and 4). In addition, lymphoid tissues of 20-day-old embryos from these hens were also investigated for the presence of CAV. CAV was detected in the gonads and of 5/6 and 11/22 of the vaccinated hens and in some hens also in the spleen alone. Embryos from 7/8 and 5/18 of these hens were positive. In the non-vaccinated flocks, CAV was detected in the gonads of 11/34 and 10/10 hens in flocks 1 and 4, respectively. In addition, 11 birds in flock 1 had positive spleens. CAV DNA was detected in 3/11 and 2/10 of their embryos. CAV-positive gonads and embryos were detected in samples from hens with moderate as well as high VN antibody titers. Vaccinated chickens positive for CAV in the gonads and in their embryos had VN titers ranging from >1:512 to <1:2048. In non-vaccinated chickens, the VN titers of CAV positive chickens ranged from 1:128 to 1:4096. These results demonstrate that CAV genome can remain present in the gonads of hens in commercial broiler breeder flocks even in the presence of high neutralizing antibody titers that have been associated with protection against CAV vertical transmission. It also suggests that transmission to the progeny may occur irrespectively of the level of the humoral immune response in the hens.

Chicken Infectious Anemia Virus: An Example of the Ultimate Host–Parasite Relationship

Chicken infectious anemia virus (CIAV) is a resistant and ubiquitous virus of chickens causing disease in young chickens and immunosuppression in all birds. This paper reviews the current knowledge of CIAV with a focus on new findings indicating that immunosuppressive effects have not been fully appreciated, especially as they relate to the development of antigen-specific cytotoxic T cells. A more complete understanding of the immunosuppressive effects of CIAV emphasizes the need for better vaccines, especially for the broiler industry. In addition, a new model is proposed for the control of viral replication in the reproductive tract of specific-pathogen-free chickens, which may be latently infected. This model suggests that virus transcription is controlled by viral enhancer and repressor elements, which are regulated by different hormones. As a consequence, CIAV has a well-adapted relationship with its host, avoiding immune detection, ensuring passage of virus to the next generation, and eliciting limited pathology to the host.

Influence of genetic resistance of the chicken and virulence of Marek's disease virus (MDV) on nitric oxide responses after MDV infection

Nitric oxide (NO), a free radical produced by the enzyme NO synthase (NOS), is a potent antiviral agent in addition to having immune regulating functions. Recently, it was reported that chickens resistant (N2a, MHC: B21B21) to the development of Marek's disease (MD) had a greater potential to produce NO than MD-susceptible chickens (P2a, MHC: B19B19). This difference was shown by measuring NO levels in chick embryo fibroblast cultures obtained from these chickens after treatment with lipopolysaccharide and recombinant chicken interferon-gamma (IFN-gamma). To extend these results, the levels of NO in blood plasma from N2a and P2a chickens inoculated with the nonattenuated JM-16 strain of MD virus (MDV) were examined. In four out of five experiments, N2a chickens had increased NO levels at 7 days postinoculation (DPI). In contrast, P2a chickens challenged with JM-16 had a significant increase in NO in only one of four experiments, and in that experiment the increase was delayed (10 DPI) compared with N2a chickens. Attenuation abrogated MDV-induced NO in chickens. Inoculation with MDV strains ranging from mild to very virulent plus showed that the more virulent strains induced the highest level of NO in blood plasma, suggesting a role of NO in the pathogenesis of MD with more virulent strains. On the basis of quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR) assays for analysis of mRNA expression, IFN-gamma does not appear to be the primary inducer of inducible (i)NOS gene expression during MDV infection. iNOS gene expression and NO production are mediated during the cytolytic phase of MDV infection on the basis of real-time RT-PCR assays with primers specific for glycoprotein B, a late gene expressed only during the cytolytic phase of MDV infection. These findings implicate NO as a factor potentially involved in increasing virulence of MDV, possibly through immune suppression.

Interactions of poult enteritis and mortality syndrome-associated reovirus with various cell types in vitro

An avian reovirus, ARV-CU98, has recently been isolated from poults experiencing poult enteritis and mortality syndrome (PEMS). To further understand ARV-CU98 and its role in PEMS, the current study investigates interactions of ARV-CU98 with various cell types in vitro. When macrophages, B cells, T cells, and liver cells of chicken or turkey origin were co-incubated with ARV-CU98, only cells of liver origin demonstrated cytopathic effects, the presence of viral antigen, and reduced metabolic activity over time. Furthermore, distinctive pockets of viral particles were evident in electron microscopic examination of a chicken hepatocellular carcinoma (LMH) cell line, but not in a chicken macrophage cell line (MQ-NCSU) co-incubated with virus. Additional evidence of viral replication in LMH, cells but not MQ-NCSU cells was demonstrated by the presence of two viral bands (43 and 145 kD size) in cell lysates from LMH cells exposed to ARV-CU98. Although not capable of being infected by ARV-CU98, MQ-NCSU cells do appear to be activated by the virus since IL-1 mRNA expression is increased in MQ-NCSU cells 2 h after addition of the virus. LMH cells exposed to the virus demonstrate a decrease in IL-1 mRNA expression by 8 to 10 h after addition of the virus, perhaps corresponding to the initiation of infection by the virus. In conclusion, this study demonstrates that ARV-CU98 actively infects and replicates in LMH cells, but not in lymphocytes or macrophages, suggesting that the liver may be a target and site of replication of ARV-CU98 in poults experiencing PEMS.

Isolation of a reovirus from poult enteritis and mortality syndrome and its pathogenicity in turkey poults

Poult enteritis and mortality syndrome (PEMS) is an acute, infectious intestinal disease of turkey poults, characterized by high mortality and 100% morbidity, that decimated the turkey industry in the mid-1990s. The etiology of PEMS is not completely understood. This report describes the testing of various filtrates of fecal material from control and PEMS-affected poults by oral inoculation into poults under experimental conditions, the subsequent isolation of a reovirus, ARV-CU98, from one of the PEMS fecal filtrates, and in vivo and in vitro studies conducted to determine the pathogenicity of ARV-CU98 in turkey poults. In order to identify a filtrate fraction of fecal material containing a putative etiologic agent, poults were challenged in two independent experiments with 220- and 100-nm filtrates of fecal material from PEMS-negative and PEMS-positive poults. The 100-nm filtrate was chosen for further evaluation because poults inoculated with this filtrate exhibited mortality and significantly lower (P < or = 0.05) body weight and relative bursa weight, three clinical signs associated with PEMS. These results were confirmed in a third experiment with 100-nm fecal filtrates from a separate batch of PEMS fecal material. In Experiment 3, body weight and relative bursa and thymus weights were significantly lower (P < or = 0.05) in poults inoculated with 100-nm filtrate of PEMS fecal material as compared with poults inoculated with 100-nm filtrate of control fecal material. Subsequently, a virus was isolated from the 100-nm PEMS fecal filtrate and propagated in liver cells. This virus was identified as a reovirus on the basis of cross-reaction with antisera against avian reovirus (FDO strain) as well as by electrophoretic analysis and was designated ARV-CU98. When inoculated orally into poults reared under controlled environmental conditions in isolators, ARV-CU98 was associated with a higher incidence of thymic hemorrhaging and gaseous intestines. In addition, relative bursa and liver weights were significantly lower (P < or = 0.05) in virus-inoculated poults as compared with controls. Virus was successfully reisolated from virus-challenged poults but not from control birds. Furthermore, viral antigen was detected by immunofluorescence in liver sections from virus-challenged poults at 3 and 6 days postinfection and virus was isolated from liver at 6 days postinfection, suggesting that ARV-CU98 replicates in the liver. In addition to a decrease in liver weight, there was a functional degeneration as indicated by altered plasma alanine aminotransferase and aspartate aminotransferase activities in virus poults as compared with controls. Although this reovirus does not induce fulminating PEMS, our results demonstrated that ARV-CU98 does cause some of the clinical signs in PEMS, including intestinal alterations and significantly lower relative bursa and liver weights. ARV-CU98 may contribute directly to PEMS by affecting the intestine, bursa, and liver and may contribute indirectly by increasing susceptibility to opportunistic pathogens that facilitate development of clinical PEMS.

Cellular responses in chickens treated with IFN-alpha orally or inoculated with recombinant Marek's disease virus expressing IFN-alpha

Mammalian type I interferons (IFN-alpha/beta) are potent mediators of innate antiviral immune responses, in particular through enhancement of natural killer (NK) cell cytotoxicity. Recently, chicken IFN-alpha (ChIFN-alpha) has been identified and shown to ameliorate Newcastle disease virus (NDV) infection when given to chickens at relatively high concentrations in the drinking water. In this report, the effect of recombinant ChIFN-alpha (rChIFN-alpha) on NK cell cytotoxicity was examined using (51)Cr-release assays. NK cell cytotoxic activity was also analyzed following inoculation with attenuated Marek's disease virus (MDV) serotype 1 strain R2/23 and a recombinant MDV (parent strain R2/23)-expressing ChIFN-alpha [rMDV(IFN-alpha)]. Treatment of chickens with high doses of rChIFN-alpha in the drinking water significantly decreased NK cell cytotoxicity compared with untreated chickens over a 7-day period. Inoculation of chickens with R2/23 significantly decreased NK cell cytotoxicity as well, whereas the rMDV(IFN-alpha) had no effect on NK cell cytotoxicity. Treatment of chicken embryo cell cultures with rChIFN-alpha inhibited replication of the very virulent MDV RB-1B strain in vitro, and oral treatment of chickens with rChIFN-alpha reduced MDV R2/23 replication in vivo.

Transactivation of latent Marek's disease herpesvirus genes in QT35, a quail fibroblast cell line, by herpesvirus of turkeys

The QT35 cell line was established from a methylcholanthrene-induced tumor in Japanese quail (Coturnix coturnix japonica) (C. Moscovici, M. G. Moscovici, H. Jimenez, M. M. Lai, M. J. Hayman, and P. K. Vogt, Cell 11:95-103, 1977). Two independently maintained sublines of QT35 were found to be positive for Marek's disease virus (MDV)-like genes by Southern blotting and PCR assays. Sequence analysis of fragments of the ICP4, ICP22, ICP27, VP16, meq, pp14, pp38, open reading frame (ORF) L1, and glycoprotein B (gB) genes showed a strong homology with the corresponding fragments of MDV genes. Subsequently, a serotype 1 MDV-like herpesvirus, tentatively name QMDV, was rescued from QT35 cells in chicken kidney cell (CKC) cultures established from 6- to 9-day-old chicks inoculated at 8 days of embryonation with QT35 cells. Transmission electron microscopy failed to show herpesvirus particles in QT35 cells, but typical intranuclear herpesvirus particles were detected in CKCs. Reverse transcription-PCR analysis showed that the following QMDV transcripts were present in QT35 cells: sense and antisense meq, ORF L1, ICP4, and latency-associated transcripts, which are antisense to ICP4. A transcript of approximately 4.5 kb was detected by Northern blotting using total RNA from QT35 cells. Inoculation of QT35 cells with herpesvirus of turkeys (HVT)-infected chicken embryo fibroblasts (CEF) but not with uninfected CEF resulted in the activation of ICP22, ICP27, VP16, pp38, and gB. In addition, the level of ICP4 mRNA was increased compared to that in QT35 cells. The activation by HVT resulted in the production of pp38 protein. It was not possible to detect if the other activated genes were translated due to the lack of serotype 1-specific monoclonal antibodies.

Distribution of chicken anaemia virus in the reproductive tissues of specific-pathogen-free chickens

The specific-pathogen-free (SPF) flocks of chickens maintained by the Department of Microbiology and Immunology at Cornell University became infected, inadvertently, with chicken anaemia virus (CAV), as demonstrated by seroconversion. Chickens from five flocks representing three different strains were examined for the presence of CAV using nested PCR. Virus was detected in ovaries, infundibula, vas deferentia, testes and spleens. Ovaries were positive in 38 to 72% of the hens in four flocks with 13 to 56 birds examined per flock. Interestingly, the ovaries were often the only positive tissues, while a few hens had only positive spleens. In roosters, the vas deferens was positive in 30 to 79% of the birds with 5 to 19 birds examined per flock; the vas deferens was the only positive tissue in 20 to 37%. Individual cells in the theca externa and rare epithelial cells in the infundibular epithelium were positive for CAV by in situ PCR. Positive cells were not detected in testes or vas deferentia. The SH-1 strain of CAV was isolated from these tissues and partially sequenced. Only minor sequence differences were found compared to CIA-1 and Cux-1. Embryos from matings between persistently infected dams and sire had CAV-positive cells in mesenchyme near the developing vertebral column. The data show that CAV persists in the reproductive tissues far longer than previously thought, and that it can be vertically transmitted from persistently infected birds.

Humoral immune responses to chicken infectious anemia virus in three strains of chickens in a closed flock

This is a comparative study on seroconversion to chicken infectious anemia virus (CIAV) in a closed flock of specific-pathogen-free chickens undergoing a natural outbreak and after vaccination of some of these flocks with a commercial, live vaccine. The N2a strain (B21B21 haplotype) had the highest seroconversion after natural infection (94%) or vaccination (100%), followed by the P2a strain (B19B19) at 75%-82% seroconversion after natural infection and 85% seroconversion after vaccination. The S13 (B13B13) chickens were 26% seropositive after natural infection and 75% seropositive after vaccination. N2a chickens with polymerase chain reaction (PCR)-positive tissues were 97% seropositive compared to 80%-83% PCR-positive and seropositive for the P2a chickens and only 8% seropositive and PCR-positive for the S13 chickens. Seroconversion occurred at or near sexual maturity after natural infection in seven flocks studied.

Expression of cytokine genes in Marek's disease virus-infected chickens and chicken embryo fibroblast cultures

The role of cytokines in the pathogenesis and immunity of Marek's disease (MD), a herpesvirus-induced T-cell lymphoma in chickens, is poorly understood. Two different experiments were used to examine the potential role of particular cytokines in the pathogenesis and immune responses of MD. First, chicken embryo fibroblasts (CEF) were stimulated with lipopolysaccharide (LPS) and/or recombinant chicken interferon-gamma (rChIFN-gamma) and used to develop techniques for examining transcription of IFN-alpha, IFN-gamma, inducible nitric oxide synthase (iNOS), interleukin (IL)-1beta, IL-2, IL-6 and IL-8 by reverse transcription-polymerase chain reaction (RT-PCR). Addition of LPS and/or rChIFN-gamma resulted in the up-regulation of mRNA for iNOS, IL-1beta and IL-6, while IFN-gamma was up-regulated by LPS alone. IL-2 was down-regulated by the treatments. Second, to determine the effects of Marek's disease herpesvirus (MDV) infection on cytokine transcription in vivo, chickens were infected with MDV at 21 days of age and examined at 7 days post-infection (p.i.) (exp. 1) or were infected with MDV at 1 day of age and examined from 3 to 15 days p.i. (exp. 2). In MDV-infected chickens, IFN-gamma transcription was up-regulated as early as 3 days p.i. until the termination of the experiment at 15 days p.i., while iNOS and IL-1beta were up-regulated between 6 and 15 days p.i. Infection of 1-day-old chicks increased levels of mRNA for IFN-gamma and iNOS between 16- and 64-fold at 9 days p.i. These results suggest that IFN-gamma and iNOS may play an important role in the pathogenesis of MD.

Inhibitory effects of nitric oxide and gamma interferon on in vitro and in vivo replication of Marek's disease virus

The replication of Marek's disease herpesvirus (MDV) and herpesvirus of turkeys (HVT) in chicken embryo fibroblast (CEF) cultures was inhibited by the addition of S-nitroso-N-acetylpenicillamine, a nitric oxide (NO)-generating compound, in a dose-dependent manner. Treatment of CEF culture, prepared from 11-day-old embryos, with recombinant chicken gamma interferon (rChIFN-gamma) and lipopolysaccharide (LPS) resulted in production of NO which was suppressed by the addition of N(G)-monomethyl L-arginine (NMMA), an inhibitor of inducible NO synthase (iNOS). Incubation of CEF cultures for 72 h prior to treatment with rChIFN-gamma plus LPS was required for optimal NO production. Significant differences in NO production were observed in CEF derived from MDV-resistant N2a (major histocompatibility complex [MHC], B(21)B(21)) and MDV-susceptible S(13) (MHC, B(13)B(13)) and P2a (MHC, B(19)B(19)) chickens. N2a-derived CEF produced NO earlier and at higher levels than CEF from the other two lines. The lowest production of NO was detected in P2a-derived CEF. NO production in chicken splenocyte cultures followed a similar pattern, with the highest levels of NO produced in cultures from N2a chickens and the lowest levels produced in cultures from P2a chickens. Replication of MDV and HVT was significantly inhibited in CEF cultures treated with rChIFN-gamma plus LPS and producing NO. The addition of NMMA to CEF treated with rChIFN-gamma plus LPS reduced the inhibition. MDV infection of chickens treated with S-methylisothiourea, an inhibitor of iNOS, resulted in increased virus load compared to nontreated chickens. These results suggest that NO may play an important role in control of MDV replication in vivo.

Specific and nonspecific immune responses to Marek's disease virus

Marek's disease (MD) virus (MDV) has provided an important model to study immune responses against a lymphoma-inducing herpesvirus in its natural host. Infection in chickens starts with a lytic infection in B cells, followed by a latent infection in T cells and, in susceptible birds, T cell lymphomas develop. Non-specific and specific immune responses are important for the control of virus infection and subsequent tumor development. Interferon-gamma and nitric oxide are important for the control of virus replication during the lytic phase of infection and are also important to prevent reactivation of MDV replication in latently infected and transformed cells. Cytotoxic T cells (CTLs) are the most important of the specific immune responses in MDV. In addition to antigen-specific CTL against MDV proteins pp38, glycoprotein B (gB), Meq, and ICP4, ICP27-specific CTL can also be detected as early as 6 to 7 days post infection. The epitope for gB recognized by CTLs from P2a (MHC: B(19)B(19)) chickens has been localized to the Eco47III-BamHI (nucleotides 1515-1800) fragment. A proposed model for the interactions of cytokines and immune responses as part of the pathogenesis of MD is discussed.

Comparative susceptibility of Marek's disease cell lines to chicken infectious anemia virus

Chicken infectious anemia virus (CIAV) is known to infect and replicate in various Marek's disease chicken cell lines (MDCCs) derived from Marek's disease (MD) tumors. One line, MDCC-MSB1, has been the substrate used in most studies. We compared a total of 26 MDCCs, including two sublines of MDCC-MSB1, MSB1 (L) and MSB1 (S), four other MD tumor-derived lines, and 20 lines derived from MD virus-induced local lesions, for susceptibility to the Cux-1 and CIA-1 strains of CIAV. The cell lines represented six phenotypic groups of T cells based on the expression of CD4, CD8, and TCR-2 and -3 surface markers. Susceptibility was measured by the number of cells positive for viral antigen in immunofluorescence (IF) tests at 3-10 days postinfection. No clear-cut differences were found in susceptibility related to phenotype, although CD4-/8+ lines and CD4-/8- lines might be more susceptible than CD4+/8- lines. However, several individual lines were more susceptible to Cux-1 than the two MSB1 sublines tested. Contrary to an earlier report, cells of MDCC-CU147, a CD8+, TCR3+, local-lesion derived line, were found to be susceptible to CIA-1. In fact, CU147 was distinguished by very high susceptibility to both CIAV strains. In direct comparisons with MSB1, CU147 detected approximately 10-fold lower doses of virus. Also, virus spread was faster (P < 0.05) in CU147 than in MSB1 and other lines. Results from polymerase chain reaction (PCR) tests to detect infection in titrations were in general agreement with IF test results although PCR detected infection in a few terminal dilution cultures that were negative by IF.

A monoclonal antibody to ICP4 of MDV recognizing ICP4 of serotype 1 and 3 MDV strains

Monoclonal antibodies (MAbs) were prepared against ICP4 of Marek's disease virus (MDV). Mice were inoculated with ICP4 obtained from High-Five insect cells infected with a recombinant baculovirus expressing ICP4. MAbs were selected by enzyme-linked immunosorbent assay (ELISA) using MDV-infected and control chick kidney cells as antigens. One of the MAbs, 5H8, recognized an epitope toward the carboxyl terminus of ICP4 based on staining of reticuloendotheliosis virus-transformed cells transfected with full-length and truncated ICP4 constructs. This MAb recognized ICP4 in chicken embryo fibroblasts (CEFs) infected with MDV strains JM16 and HVT but not with SB-1 strain. Using Western blot analysis a protein of 155 kDa was detected in CEFs infected with JM16 and HVT strains.

Genome analysis of Marek's disease virus strain CVI-988: effect of cell culture passage on the inverted repeat regions

The genomes of different derivatives of Marek's disease virus (MDV) strain CVI-988, a low oncogenic isolate of a serotype 1 MDV, were analyzed by restriction enzyme analyses to detect whether alterations occurred after passages in cell culture. DNA molecules of strain 988 isolated directly from blood cells contained mainly two copies of the 132-bp repeat sequence previously reported within BamH1-H and -D fragment as previously reported for more virulent MDV strains. Although a minority of virus particles showed repeat amplification was already at the fifth passage level, amplification mainly occurred between passages 17 and 34 in cell culture. In addition, a 400-bp deletion was detected within the BamH1-A fragment of two derivatives of CVI-988, 988C and 988C/R6.

Detection of duck enteritis virus by polymerase chain reaction

Duck enteritis virus (DEV), a herpesvirus, is the causative agent of duck viral enteritis in free-flying, feral, and domesticated members of the Anatidae family. HindIII-digested DEV DNA was cloned into the plasmid pBluescript, and a 1.95-kb fragment was sequenced. This fragment codes for the 3' region of the DEV homologues of varicella-zoster virus (VZV) open reading frame (ORF) UL6 and the 5' region of VZV UL7. Alignment of the putative peptide fragments for DEV UL6 and UL7 showed a 64% and 37% identity with VZV UL6 and UL7, respectively. Primers located in the highly conserved domain of the UL6 gene were used for a polymerase chain reaction (PCR) assay, which was able to amplify DEV DNA. The PCR assay also amplified DEV DNA from the original outbreak samples and/or after passage in Muscovy duck embryos.

Open reading frame L1 of Marek's disease herpesvirus is not essential for in vitro and in vivo virus replication and establishment of latency

Two mutant CV1988 Marek's disease virus (MDV) strains were developed in which a part of ORF L1 was replaced by lacZ with the SV40 early promoter. These mutant strains, CVIL1LacZ-A and -B, were inoculated into chickens to test the hypothesis that ORF L1 is involved in the induction and/or maintenance of latency. Mutant virus could be reisolated from lymphocytes obtained from chickens during both the lytic and latent phase of infection, indicating that ORF L1 is not essential for the induction and/or maintenance of latency or the reactivation from latency. Beta-galactosidase-positive lymphocytes were detected during the latent infection demonstrating that the SV40 early promoter can be active in recombinant MDV strains during latent infection. Although the insertion of lacZ was stable in cell culture, recombination within lacZ and the BamHI-L fragment was observed during in vivo infection.

Cytotoxic T lymphocyte response in chickens immunized with a recombinant fowlpox virus expressing Marek's disease herpesvirus glycoprotein B

Previously, we demonstrated that cytotoxic T lymphocytes (CTLs) from MHC: B19B19 and MHC: B21B21 chickens inoculated with a non-oncogenic Marek's disease virus (MDV) vaccine strain, SB-1/12 can lyse syngeneic reticuloendotheliosis virus (REV)-transformed cell lines expressing MDV pp38 or gB genes. In this study, we report the characterization of MDV gB-specific CTLs in chickens immunized with recombinant fowlpox virus expressing MDV gB gene (rFPV-gB). Spleen cells from rFPV-gB inoculated chickens (MHC: B19B19), depleted for CD4+, CD8+, TCR gamma delta+, TCR alpha beta 1+ or TCR alpha beta 2+ cells were used as effector cells in chromium release assays. Effector cells depleted of CD8+ or TCR alpha beta 1+, but not CD4+, TCR gamma delta+ or TCR alpha beta 2+ markedly reduced the percentage of specific release (%SR). Compared to the %SR caused by the SB-1/12-sensitized CTLs, the %SR caused by rFPV-gB-sensitized CTLs was low, but statistically significant. This is a first report on the induction of MDV gB-specific CD8+ CTLs in chickens immunized with rFPV-gB vaccine.

Relationship between the immunosuppressive potential and the pathotype of Marek's disease virus isolates

Isolates of Marek's disease virus (MDV) representing three pathotypes of differing virulence were compared for relative immunosuppressive properties in genetically susceptible P2a-strain and genetically resistant N2a-strain chickens. Criteria of immunosuppression were 1) persistence of early cytolytic infection (i.e., a delay or failure to enter latency) in lymphoid organs, 2) atrophy of the bursa of Fabricius and thymus as measured by organ weight proportional to body weight at 8 and 14 days postinfection (DPI), and 3) histopathologic evidence of necrosis and atrophy in lymphoid organs. No significant differences in infection level were observed among the pathotypes during the early (4-5 DPI) period of infection. However, the extent of persistent cytolytic infection at 7-8 DPI, based on numbers of tissues positive and mean scores in immunofluorescence tests, was greater (P < 0.05) for three isolates (RK1, 584A, 648A) in the highest virulence pathotype (very virulent-plus MDV [vv + MDV]) than for two isolates (JM16, GA5) in a lower virulence (virulent MDV [vMDV]) pathotype. Results from two isolates (RB1B, Md5) classified in the intermediate very virulent pathotype (very virulent MDV [vvMDV]) fell between those from the other two pathotypes. Similarly, there was a stepwise effect of viral pathotype in which the vv + MDV isolates caused the most severe damage to lymphoid organs in terms of atrophy (relative organ weights) and histopathologic changes. Organs from chickens infected with vv + MDVs showed little recovery between 8 and 14 DPI. The vMDV isolates caused the least severe damage, and lymphoid organs showed a significant return toward normal by 14 DPI; vvMDV isolates induced intermediate degrees of atrophy and recovery. The same pattern of relationship between virulence pathotype and degree of bursal and thymic atrophy was also observed in genetically resistant N2a chickens. These results suggest that the degree of immunosuppression is linked to virulence and that a simple measure of atrophic changes (relative organ weights) in the bursa of Fabricius and thymus might be useful in determining the pathotype classification of new MDV isolates. The basis for differences in immunosuppressive potential of MDV isolates needs further clarification.

Characterization of Marek's disease herpesvirus-specific cytotoxic T lymphocytes in chickens inoculated with a non-oncogenic vaccine strain of MDV

Previously we have reported that reticuloendotheliosis virus (REV)-transformed cell lines expressing Marek's disease virus (MDV) genes pp38, meq or gB were lysed by syngeneic MDV-specific splenocytes from major histocompatibility complex (MHC):B9B19 and MHC:B1B21 chickens. In contrast, REV-transformed cell lines expressing the MDV gene ICP4 were only lysed by syngeneic MDV-specific splenocytes from MHC:B21B21 chickens. In this study we report that this syngeneic cell-mediated immune response is induced by cytotoxic T lymphocytes (CTL). Splenocytes from MDV vaccine strain, SB-1 inoculated MHC:B19B19 and MHC:B21B21 chickens, depleted for CD4+, CD8+, TCR gamma delta +, TCR alpha beta 1+ and/or TCR alpha beta 2+ cells, were used as effector cells in chromium-release assays. Effector cells depleted of CD8+ or TCR alpha beta 1+, but not TCR gamma delta + or TCR alpha beta 2+, markedly reduced the MDV-specific release. Depletion of CD4+ effector cells did not influence the specific release significantly. This is the first report on identification of virus-specific CD8+ CTL in chickens inoculated with a non-oncogenic vaccine strain of MDV.

A hypervariable region in VP1 of chicken infectious anemia virus mediates rate of spread and cell tropism in tissue culture

Chicken infectious anemia virus (CIAV) is a unique infectious agent with an amino acid composition that has been found to be remarkably conserved even in isolates from different parts of the world. We have characterized field isolates of CIAV which vary significantly in terms of their abilities to replicate in culture, demonstrating a biological difference between isolates. Two sublines of MDCC-MSB1 cells that differ in their abilities to support CIAV were identified. In the MSB1(S) subline the CIA-1 isolate of CIAV was found to be less cytopathogenic than the prototype Cux-1(C) isolate; the MSB1(L) subline, which supports Cux-1(C) replication, was found to be nonpermissive for CIA-1. Alignments of the VP1 sequences of previously examined isolates with those of the field isolates CIA-1 and L-028 and the culture-adapted ConnB isolate revealed a previously unreported hypervariable region spanning amino acid positions 139 to 151. Chimeras of Cux-1(C) and CIA-1 were constructed to examine the potential for this region to affect cytopathogenicity. Transfer of a 316-bp region of Cux-1(C) open reading frame 1 into CIA-1 produced a virus with a cytopathogenic profile typical of Cux-1(C), indicating that one or both of the amino acid differences at positions 139 and 144 affect the rate of replication or the spread of infection. Transfection experiments with additional chimeras indicated that the inability of CIA-1 to replicate in MSB1(L) cells is mediated by a larger region of the genome which contains the hypervariable region in addition to upstream amino acid differences. Analysis of chimeras excluding the entire region of open reading frame 1 suggested the presence of a secondary mediator in the progression of infection in culture that was localized to a region containing a single nucleotide difference which results in amino acid differences in both VP2 (V-153) and the nuclear localization signal of VP3 (C-118). Immunofluorescence assays indicated an increased cytoplasmic distribution of VP3 and a general lack of VP3-associated apoptotic bodies in infections of CIA-1 and chimeras containing V-153 or C-118, as opposed to a primarily nuclear distribution and association with well-formed apoptotic bodies in Cux-1(C)-infected cells.

Syngeneic Marek's disease virus (MDV)-specific cell-mediated immune responses against immediate early, late, and unique MDV proteins

Marek's disease (MD) infection has been controlled effectively by vaccination using nononcogenic and/or attenuated oncogenic Marek's disease virus (MDV) vaccines. Thus far, there is little knowledge on the role of cell-mediated immune (CMI) responses during MDV infection or vaccination. To elucidate the importance of MDV proteins in CMI responses, the pp38, Meq, ICP4, or ICP22 genes of an oncogenic strain, GA and the gB, ORF A, A41, or L1 genes of a highly oncogenic strain, RB1B were stably transfected into reticuloendotheliosis virus (REV)-transformed lymphoblastoid cells, CU-91 (MHC: B19B19) and CU-205 (MHC: B21B21). Cell lines positive for MDV gene transcription and/or protein expression were used in a standard 4-hr chromium release assay. Effector cells for this assay were obtained from splenocytes of chickens infected with the oncogenic strain, JM-16/13 or the nononcogenic vaccine strain, SB-1/12. Cell lines expressing MDV pp38, Meq, or gB were lysed by syngeneic but not allogeneic MDV-sensitized splenocytes obtained from chickens of B19B19 and B21B21 haplotypes. However, syngeneic CMI responses against ICP4 were detected only in B21B21 chickens. CMI responses were not detected against B19B19 and B21B21 cell lines expressing A41, L1, ORF A, or ICP22. This report suggests that syngeneic CMI responses against pp38, Meq, ICP4, and gB of GA and RB1B strains, respectively, can be induced in chickens inoculated with JM16/13 or SB-1/12. The difference in CMI response to ICP4 in genetically susceptible (B19B19) and genetically resistant (B21B21) chickens may be an important factor in genetic resistance.

Syngeneic lysis of reticuloendotheliosis virus-transformed cell lines transfected with Marek's disease virus genes by virus-specific cytotoxic T cells

Cell-mediated immune responses against Marek's disease virus (MDV) antigens were examined using reticuloendotheliosis virus (REV)-transformed cell lines of two haplotypes (B19B19 and B13B13). These cell lines were stably transfected with cloned fragments of MDV DNA resulting in the expression of the MDV-specific phosphoprotein pp38. Effector cells were obtained from P2a (B19B19) and S13 (B13B13) chickens at 7 days post inoculation with REV, oncogenic or attenuated serotype 1 MDV (JM-16/O and JM-16/A, respectively), serotype 2 MDV (SB-1), or herpesvirus of turkeys (HVT). Transfection of MDV genes did not influence the expression of Class I major histocompatibility complex antigens. The optimal effector to target cell ratio was determined to be 100:1. REV-sensitized effector cells lysed REV cell lines and REV cell lines transfected with MDV DNA in a syngeneic fashion. Effector cells from chickens inoculated with JM-16/O, JM-16/A, SB-1 or HVT lysed only the syngeneic, transfected cell lines, but not the parent REV cell lines. The percentage specific release caused by the MDV-sensitized effector cells was low, but statistically significant.

Cell-mediated immune effector functions in chickens

Cell-mediated immune responses form an important part of the protection against intracellular pathogens. The MHC Class I and Class II antigens are important for the proper presentation of degraded proteins to cytotoxic T lymphocytes (CTL) and helper T cells, respectively. Recent developments in the knowledge of the molecular structure of the MHC in relation to antigen presentation are discussed. Although CTL are important, there is a paucity of information concerning their relevance for the control of viral diseases in poultry. A newly developed approach of stable transfection of viral genes into cell lines transformed by reticuloendotheliosis virus has shown promise as a method to define proteins, which are important for the induction of cell-mediated immunity.

Inhibition of the in vitro development of Eimeria tenella in chick kidney cells by immune chicken splenocytes

An in vitro microbicidal assay was used to study the immune response of chickens to Eimeria tenella by measuring the effect of splenocytes from immunized chickens on intracellular development of E. tenella. Splenocytes were prepared from specific-pathogen-free chickens [strain P2a(B19B19) or N2a(B21B21)], immunized one, two, or three times with non-lethal doses of E. tenella. Twelve hours following infection of chick kidney cells (CKCs) with E. tenella sporozoites, splenocytes were added to infected CKCs for 4, 8, or 36 hours. Intracellular E. tenella development was allowed to continue until 72 hours after sporozoite infection, when intracellular development was quantitated by counting merzoites. Immune splenocytes significantly inhibited E. tenella intracellular development after one, two, or three immunizations. Significant inhibition occurred with 4, 8, or 36 hours of coculture and was no greater with longer co-culture times. Immune P2a splenocytes significantly reduced merozoite development in both syngeneic P2a and allogeneic N2a infected CKCs, whereas immune N2a splenocytes had little effect on E. tenella development in either N2a or P2a infected CKCs. These results suggest that immune splenocytes are induced and act relatively rapidly and are not apparently restricted by the major histocompatibility complex, consistent with natural killer cell activity.

Enhanced expression of the Marek's disease virus-specific phosphoproteins after stable transfection of MSB-1 cells with the Marek's disease virus homologue of ICP4

Phosphoprotein pp38, coded for by the BamHI-H fragment of the Marek's disease herpesvirus (MDV) genome is expressed in tumor cells and tumor cell lines. pp38 is associated with two other phosphoproteins, pp41 and pp24, and can be detected in a small percentage of tumor cells by indirect immunofluorescence assays (IIFA). The importance of MDV ICP4 for the regulation of pp38 expression was examined in the following MSB-1-derived cell lines stably transfected with the selection plasmid pNL1 [MDCC-CU221 (CU221)], pNL1 and the BamHI-A fragment of MDV DNA containing ICP4 (CU224), MDV ICP4 inserted in antisense direction in the eukaryotic expression vector pXT1 (CU222), or ICP4 in sense direction in pXT1 (CU223) or cotransfected with pNL1 and EcoRI-linearized BamHI-A MDV DNA (CU225, -237, -243, -244). IIFA analysis showed that CU223 had a markedly increased expression of pp38, while CU224 had a slightly increased expression. No changes were noted in CU221 or CU222, while expression of pp38 was decreased in CU225, -237, -243, and -244. Radioimmunoprecipitation assays demonstrated that the expression of all three phosphoproteins was enhanced in CU223. Steady-state transcriptional analysis showed that CU223 had increased levels of pp38-specific (1.9 and 3.3 kb) and ICP4-specific (10.0 kb) transcripts.

Resistance to Marek's disease in chickens with recombinant haplotypes to the major histocompatibility (B) complex

Genetic resistance to Marek's disease (MD) is associated with the B-F region of the MHC. The resistance of chickens possessing either of two MHC haplotypes to challenge with different strains of MDV was examined. Chickens with serologically similar MHC recombinants BR2 and BR4 (both BF2-G23) were backcrossed for four generations to the highly inbred UCD-003 line (B17B17). Heterozygotes (B17BF2-G23) were mated to produce BR2BR2 and BR4BR4 homozygotes with 93% background gene uniformity. Both genotypes were highly resistant to GA-5 MDV, having an incidence of 0 and 8% MD for BR2BR2 and BR4BR4, respectively, whereas the incidence of MD in the UCD-003 birds was above 80%. Challenge with the very virulent RB-1B strain caused 10% and 31% MD in the BR2BR2 and BR4BR4 chickens, respectively, compared with 100% and 52% in the B17B17 (UCD-003) and B23B23 (New Hampshire 105) lines, respectively. Viremia levels at 5 and 6 d postinfection were significantly lower in BR2BR2 and B23B23 than in B17B17 genotypes.