Genetic resistance to a Marek's disease transplantable tumor cell line in chicken lines selected for different immunological characters

The tumor incidence and mortality of Marek's disease (MD) were determined for 471 progeny from four pairs of lines two-way selected for different immunological characters: graft versus host reaction (GVHR) competence, IgG levels, antibody response to rabbit serum albumin (RSA), and anaphylactic shock to BSA. All chicks were inoculated at 1 wk of age with 1 to 2 x 10(6) viable cells of a MD lymphoblastoid cell line, MDCC-MSB1-41C (41 C). Tumor incidence differed significantly between the high (H) and low (L) lines of each GVHR-, IgG-, RSA-, or BSA-selected group. There were also significant differences in mortality rates between H and L lines of all selected groups. The IgG-H, BSA-H, and RSA-H lines were more resistant than their respective L lines. The H line of the GVHR-selected lines was more susceptible than the L line. Tumor regression could be detected only in the IgG- and RSA-selected lines. No definite correlation could be found between genetic resistance to 41C and genetic resistance to MD virus.

[The occurrence of Marek's disease in genetically different groups of chickens]

The occurrence of Marek's disease was studied under laboratory conditions in four genetically different groups of chickens (Brown Leghorn, F1 hybrids of the CB x IA inbred lines, pullets of the paternal branch of the grandparent stock of the Hybro meat type, and final hybrids of the White Hisex layer type) after infection with the Georgia strain of Marek's disease (MD) virus, used in two doses (1600 and 16,000 PFU per one bird). MD was diagnosed on the basis of the occurrence of macroscopic tumours; when these tumours were absent in birds which had died within 105 days from infection, the dead bodies were subjected to microscopic examination (peripheral nerves, gonads, skin, bursa of Fabricius, thymus, spleen). The size of the parenterally administered dose of the virus had no significant effect on mortality, occurrence of tumours and the MD virus in any of the groups of chickens tested. However, there was a time shift in the mortality curve in chickens infected with a lower dose. The significantly highest occurrence of MD was recorded in BrL chickens (100%). A somewhat lower occurrence of MD was recorded in the Hisex White chickens (87.8%) and in the CB x IA hybrids (73.8%). However, the dead CB x IA chickens had a higher occurrence of tumours (96.6%) than the Hisex White chickens (77.1%). The lowest MD occurrence was recorded in the pullets of the Hybro meat type (25.5%). The organ most frequently affected by tumours after infection of the birds with the Georgia strain was the liver (24.1%).

The chicken major histocompatibility complex in disease resistance and poultry breeding

Numerous studies confirm that genes in the chicken major histocompatibility complex exert major genetic control over host resistance to autoimmune, viral, bacterial, and parasitic diseases. Examples of major histocompatibility complex associations with traits of growth and reproduction in the chicken are also available. Thus, the major effects of the major histocompatibility complex on the economically important traits of disease resistance, growth, and reproduction make the major histocompatibility complex a valuable subject for intensive analysis in agricultural species. This paper examines, as a model for integration of genetics and immunology, the research on the chicken major histocompatibility complex, which confirmed its role in genetic control of disease resistance, focusing on Marek's disease, a virally induced cancer. Current knowledge of associations of the chicken major histocompatibility complex with specific disease resistance, immune response, and other economic traits are selectively reviewed. Use of major histocompatibility complex typing in the poultry industry, including speculation about future applications, is presented.

Discovery of noninfectious viral genes complementary to Marek's disease herpes virus in quail susceptible to cholesterol-induced atherosclerosis

Japanese quail genetically selected on the basis of atherosclerosis susceptibility were tested for infection by Marek's disease herpesvirus (MDV). Viral DNA was detected in the atherosclerotic aortas of susceptible (SUS) quail by the technique of DNA hybridization. Southern blot analysis demonstrated that restriction mapping of aortic DNA was specific and different from that of MDV. Screening of quail embryos by dot-blot hybridization detected that MDV DNA existed in 100% of SUS quail tested. Resistant (RES) quail were a mixed population, with 16% of embryos resembling the SUS group. Functional MDV was not found by a number of methods including virus isolation, serological test, and exposure of sentinel chicks to SUS quail. These results suggest that the SUS quail possess a portion of the MDV genome in the germline, and the viral genes have been coselected by their susceptibility to cholesterol-induced atherosclerosis.

Immune response versus susceptibility to Marek's disease

It was hypothesized that the generation of activated T cells through an efficient and rapid immune response during the early pathogenesis of Marek's disease virus (MDV) infection provides a large pool of target cells for transformation. Therefore, the correlation between genetic susceptibility to Marek's disease (MD) and in vitro mitogenic responses of lymphocytes as a measure of cell-mediated immune competence and efficiency was tested. In one series of trials, spleen cells from strains of chickens with differing levels of susceptibility to MD tumors were stimulated with graded doses of Concanavalin A (Con A) or phytohemagglutin (PHA). In a second series of trials, peripheral blood lymphocytes from individual chickens within genetic strains were tested at the same time chickens were challenged with MDV to determine susceptibility. Responsiveness was determined using one-way mixed lymphocyte reaction (MLR) tests as well as mitogen stimulation. Data from the tests comparing chicken strains supported the hypothesis in some but not all cases. The S13 chickens, which are more susceptible than P2a chickens to MD, were significantly more responsive, and highly resistant N2a chickens were significantly less responsive to Con A. In contrast, five other resistant strains were either more responsive (UCD-058, OS13) or equally responsive (UCD-140, OS5, C) to Con A when compared with P2a chickens. The PHA responses were even less predictive of MD susceptibility. No general correlation was observed between responsiveness to either mitogen or MLR tests and subsequent tumor development in trials comparing individuals within strains.

Antigen A gene of Marek's disease virus (MDV) detects two mRNA species (3.7 and 2.1 kb) in MDV- and HVT-infected cells

The gene of glycoprotein A of Marek's disease virus (MDV) detected to mRNA species (3.7 and 2.1 kb) by Northern blot hybridization. These two mRNA species were also detected in RNA extracted from herpesvirus of turkeys (HVT)-infected chick embryo fibroblasts (CEF) and from the MSB-1 cell line.

Tests of association of immunoglobulin allotype genes and viral oncogenesis in chickens

Chickens from Regional Poultry Research Laboratory (RPRL) inbred line 6(3) are resistant to virally-induced Marek's disease (MD) and lymphoid leukosis (LL) and are relatively strong regressors of virally-induced Rous sarcomas. In contrast, RPRL line 100 chickens are highly susceptible to MD and LL and are weaker regressors of Rous sarcomas than line 6(3). RPRL lines 100 and 6(3) differ for alleles at the IgG-1 (G-1) allotype locus, but have identical IgM-1 (M-1) allotype alleles. To test the possible association of the G-1 locus with variations in resistance to virally-induced tumors, homozygous and heterozygous genotypes among F3 crosses were infected. F3 chickens with different G-1 types were comparable in their resistance to MD tumors following inoculation with the JM strain of the MD virus, and for their ability to regress Rous sarcoma tumors induced by the Rous sarcoma virus (RSV) RAV-1. However, following RAV-1 virus infection a smaller proportion of G-1a/G-1aF3 or F4 birds developed LL tumors than G-1a/G-1e and G-1e/G-1e birds. Genes determining immunoglobulin heavy chains were therefore associated with a recessive resistance to B-cell lymphomagenesis in chickens.

Ontogeny of con A and PHA responses of chicken blood cells in MHC-compatible lines 6(3) and 7(2)

The development of T cell responsiveness to Con A and PHA was examined in two MHC-compatible inbred chicken lines, RPRL 6(3) and 7(2), at ages 2 to 118 days posthatching. These lines are respectively resistant or susceptible to Marek's disease, a naturally occurring, virally induced T cell lymphoma. Between-line comparisons were made of optimal in vitro responses of diluted serum-free blood cells to each mitogen in two groups of chicks tested over ages 2 to 63 and 41 to 118 days. Over 2 to 63 days, Con A responses increased with age at the same rate in each line, but 7(2) responses averaged 2.3 times higher than 6(3). The increase with age was dependent on blood lymphocyte counts, which also increased with age in parallel in both lines. In contrast, the between-line difference in responsiveness was dependent on intrinsic reactivity of cells as well as lymphocyte counts. Covariance analysis was used to estimate that line 7(2) was 1.4 times higher than 6(3) in intrinsic cell reactivity, after accounting for the effect of the twofold higher blood lymphocyte counts in 7(2), and that this intrinsic difference contributed almost one-half the total difference. Over 41 to 118 days Con A responses no longer increased with age, although lymphocyte counts were still increasing, and the line difference (2.6 times) was now almost entirely contributed by a 2.3-fold superiority of 7(2) blood cells in intrinsic reactivity. The line difference in PHA responses was the reverse of the above in young chicks, with 6(3) responses greater than 7(2) in spite of lower lymphocyte counts. In additional chicks tested over 5 to 26 days, intrinsic reactivity of 6(3) cells to PHA averaged 4.5 times higher than 7(2). There was an abrupt decline in intrinsic reactivity of line 6(3) blood cells between 26 and 41 days to a level equal with 7(2). After this age, line 7(2) responses were 1.8 times greater than those of 6(3), and this difference was dependent solely on lymphocyte count differences. The results suggest that different gene systems mediate blood cell responses to PHA as compared with Con A. The pattern of developmental differences between inbred lines indicates the existence of distinct or partly overlapping T cell subsets with different reactivities to PHA or Con A, and of higher suppressor activity of adherent cells in line 6(3) blood. Both these differences may be related to line 6(3) inherited resistance to Marek's disease.

B5 and B15 associated with progressive Marek's disease, Rous sarcoma, and avian leukosis virus-induced tumors in inbred 15I4 chickens

RPRL 15I4 inbred chickens are nearly histocompatible except for the B5 and B15 haplotypes that determine the major transplantation antigens. B5B5 and B15B15 15I4 chickens were equally and highly susceptible to tumors induced by Marek's disease, Rous sarcoma, or avian leukosis viruses (ALV), suggesting both of these haplotypes may determine a general influence leading to tumor development. The 15I4 birds were highly susceptible to erythroblastosis, and most developed immunological tolerance to the virus after ALV infection.

Resistance to a malignant lymphoma in chickens is mapped to subregion of major histocompatibility (B) complex

A genetic recombinant within the major histocompatibility (B) complex of the chicken has revealed the chromosomal subregion effecting resistance to Marek's disease--a malignant lymphoma induced by a herpesvirus. The recombinant, BF21-G19, occurred spontaneously among the progeny of a male heterozygous for resistant BF21-G21 and susceptible BF19-G19 haplotypes. Exposure to Marek's disease of families segregating for the recombinant showed that this new F-G arrangement conferred a level of resistance equivalent to that of the resistant parental haplotype. Thus, a gene, or genes, within or closely linked to the B-F region of the B complex appears to be responsible for the observed resistance to Marek's disease.

Tests of association of lymphocyte alloantigen genotypes with resistance to viral oncogenesis in chickens. 1. Marek's disease in F7 progeny derived from 6(3) X 15(1) crosses

Marek's disease (MD)-susceptible progeny of the B5B5 genotype from the F7 generation derived from crosses of Regional Poultry Research Laboratory inbred lines 6(3) and 15(1) were tested for variation in MD resistance associated with the T lymphocyte antigen loci Ly-4 and Th-1. The four double homozygous genotypic classes of Ly-4 and Th-1 were tested in a 2 X 2 design. The Ly-4bb/Th-1aa chickens were significantly more resistant to MD oncogenesis than the other three genotypes. Thus, resistance within B5B5 genotypes appears to be associated with genetic interaction between two T cell antigen loci, which are not linked with the B complex.

Transplantable Marek's disease lymphomas. I. Growth characteristics during development in two inbred lines of chickens

Lymphomas developed in the pectoral muscle of most chickens inoculated with cells from primary Marek's disease virus-induced visceral tumors obtained from chickens of the same inbred line. However, serial passaging of the lymphoma cells in histocompatible hosts generally resulted either in an eventual absence of tumor formation at the inoculation site or in tumor regression. Exceptions occurred in two experiments, where tumors grew rapidly and the hosts died early. Subsequent passaging of cells from these tumors into syngeneic recipients resulted in the development of two new transplantable Marek's disease (MD) lymphomas. These lymphomas, which were developed in chickens of related inbred lines--G-B1 and G-B2--were designated MDCT-UG1 and MDCT-UG2, respectively. Cells from the transplantable lymphomas possess different major histocompatibility complex (MHC) antigens, since G-B1 and G-B2 chickens have different MHC genotypes. A change in the cellular composition during a particular passage for both lymphomas, as indicated by marked increases in the percentage of cells possessing a MD tumor-associated surface antigen (MATSA), suggests that each arose as a result of the emergence and selection of a highly malignant clone of cells.

Influence of oncogenicity of Marek' disease virus on evaluation of genetic resistance

Resistance to Marek's disease ( MD) is, in part, genetically determined and linked to the major histocompatability complex. The genetic resistance of 9 previously characterized lines of chickens and also of the inbred UCD-003 and 4 congenic lines was evaluated by challenge with JM-10. Five lines were highly resistant. These included the N-line and two derivatives from N-line (N-2 and N-5), PDRC strain, and one of the congenic UCD lines. The PDRC genotype is unknown, but the 3 related lines carry the B21 allele and the UCD line carries the BQ allele, which appears to be similar to B21. The UCD-003 and the other 3 congenic lines were moderately resistant while S-strain, P-2 and P-5 lines were highly susceptible to JM-10. The total MD incidence varied from 0 to 100% among the lines. Challenge with highly oncogenic virus isolates like GA-5, and especially the recently isolated RB-1B, caused high incidences of MD in all lines and, thus, did not permit differentiation of genetic resistance levels as was possible with the less oncogenic JM-10.

B-haplotype influence on Marek's disease, Rous sarcoma, and lymphoid leukosis virus-induced tumors in chickens

Experiments were conducted to establish whether B-haplotype genes that determine resistance to RSV-induced tumors would also influence resistance to Marek's disease and lymphoid leukosis. Matings of line 6(3) x 15(1) F3 or F4 breeders segregating for the Ea-B locus antigens that are markers for B2 and B5 haplotypes of the B major histocompatibility complex were made to produce B2B2, B2B5, and B5B5 chicks. The chicks were infected with a standard inoculum of one of the three tumor viruses in separate experiments. The B2 haplotype from 6(3) conveyed greater resistance to tumors induced by all three viruses than the B5 from 15(1) chickens. This finding suggests that some gene(s) in the B-haplotype may determine a general ability to resist tumor formation or cause tumor regression.

Nature of genetic resistance to Marek's disease in chickens

Infection of line 6 resistant and line 7 susceptible chickens with Marek's disease virus (MDV) resulted in a depressed phytohemagglutinin (PHA) response and the presence of Marek's disease (MD) tumor-associated surface antigen (MATSA) in the spleens. At 6-10 weeks after infection, recovery in PHA response, diminution in the number of MATSA cells, and the presence of significant anti-MATSA immunity were observed in line 6 but not in line 7 chickens. Both lines had antibody-dependent cell-mediated antiviral immunity, but T-cell-mediated antiviral immunity was detected only in line 6 and the surviving line 7 chickens. Lymphoproliferative lesions were found only in line 7 chickens, an virus titers were significantly higher in line 7 than in line 6 chickens and embryos. Lymphoid organ weights and the number of lymphocytes of line 6 were significantly lower than those of line 7. These data suggests that resistance to MD in line 6 chickens was due to a) a deficiency in the aggregate number of target lymphocytes, b) a restriction in the ability to lymphocytes to nonproductively replicate MDV, and c) the involvement of cellular antiviral and antitumor immune responses.

Development and characterization of a Marek's disease transplantable tumor in inbred line 72 chickens homozygous at the major (B) histocompatibility locus

A serially transplantable Marek's disease (MD) tumor, designated MDCT-RP-3, was developed from an MD-virus-induced lymphoma (GA strain) in a pedigreed female chicken of the inbred B-histocompatible (B2/B2), line 72, and is the first MD tumor transplant to be developed in chickens both syngeneic and selected for susceptibility to MD. The MDCT-RP-3 tumor maintained its female karyotype through at least 80 passages in male 72 chickens. High doses of tumor cells caused progressively growing tumors at 5 days postinoculation and death of young 72 chicks in 7-10 days, whereas allogeneic chicks of other lines were less susceptible. Tumors frequently regressed when doses of tumor cells were low or older chickens were used. MD virus was rescued from MDCT-RP-3 cells in cell culture, and chickens surviving the early transplant response sometimes developed MD lymphomas. The tumor cells expressed MD-tumor-associated surface antigen (MATSA) and T-cell surface antigens. A serum raised in rabbits against MDCT-RP-3 cells and absorbed with normal 72 cells appeared to be reactive against MATSA on all MD tumor cells tested and is probably monospecific. Sera raised against MDCT-RP-3 in chickens also contained MATSA antibodies reactive against heterologous but not homologous MD tumor cells. Protection against transplantation of MDCT-RP-3 cells was not afforded by immunization with turkey herpesvirus vaccine. Some unvaccinated chickens that regressed MDCT-RP-3 transplant appeared to be partially immune to later development of MD lymphomas.

Cell-mediated immunity in Marek's disease: cytotoxic responses in resistant and susceptible chickens and relation to disease

Two experiments were conducted to study the cell-mediated cytotoxicity of peripheral blood leukocytes (PBL) from chickens inoculated with Marek's disease virus (MDV) against a Marek's disease-derived lymphoblastoid cell line (MSB-1) and to associate the cytotoxicity with incidence of disease. In experiment I, moderately susceptible random-bred, specific-pathogen-free chickens were inoculated with MDV (group 1), vaccinated with a herpesvirus of turkeys (HVT) and inoculated with MDV (group 2), vaccinated with HVT and inoculated with chicken kidney cells (CKC; group 3), and inoculated with CKC only (group 4). Cytotoxic activity in the PBL was detected initially during the first week after MDV inoculation and periodically throughout the observation period (groups 1, 2, and 3). Throughout the observation period, the magnitude of cytotoxic activity was similar in PBL from groups 1 and 2 chickens. The PBL from both surviving and fatally infected chickens (groups 1 and 2) were similarly cytotoxic when sampled during the first 16 days after MDV inoculation. In experiment II, inbred genetically susceptible (line 7) and resistant (line 6) chickens were used. Cytotoxic activity of PBL of significantly greater magnitude was associated with a lower mortality or incidence of gross lesions (or both) in MDV-inoculated line 6 (group B) and HVT-vaccinated and MDV-inoculated line 7 (group C) chickens compared with activity of PBL from MDV-inoculated line 7 (group A) chickens. The cytotoxic activity of PBL from individual inbred chickens did not correlate with the outcome of the infection.

Marek's disease tumor-associated surface antigen (MATSA) in resistant versus susceptible chickens

The appearance of MATSA-bearing cells in the spleens of genetically susceptible (P-line) and resistant (N-line) chickens followed similar patterns at 4 and 6 days postinoculation (PI), with 4 to 10% of the cells positive in indirect fluorescent-antibody tests. Levels of MATSA-positive cells at 10, 14, and 21 days PI continued at 6-8% in P-line birds but dropped from about 8% to below 1 or 2% in N-line birds. This pattern was seen also in virus-isolation rates from the same spleen samples. Viral internal antigens (VIA) were seen equally and with decreasing incidence in both groups at 4-10 days PI. VIA were not detected at 14 days but reappeared at 21 days, with higher levels in P-lines than inN-lines. It was concluded that genetic resistance to Marek's disease is not related to events which result in production of the putative tumor antigen, MATSA, but rather to host-controlled factors which terminate those events.

Marek's disease virus-induced tumor transplants: development and rejection in various genetic strains of chickens

This study compares the ability of strains of chickens of varied genetic resistance to Marek's disease (MD) to resist or regress both local and general reactions to transplantable tumor cells induced by a variety of MD virus strains and to transmissible lymphoid tumor cells (Olson's TLT) induced by an avian leukosis-sarcoma retrovirus. Previous studies have dealt with only a single MD transplant. Three conclusions can be drawn from our data: 1) MD virus infection alone could induce progressive tumors at the site of inoculation. 2) Progression or regression of transplant tumors was independent of genetic susceptibility to MD. 3) Incidence of virus-induced host tumors was dependent upon genetic susceptibility to MD.

Pathogenicity of low-virulence Marek's disease viruses in normal versus immunologically compromised chickens

To learn whether "low virulence" isolants of Marek's disease (MD) virus have a low inherent oncogenic potential, 3 isolants (CU-1, CU-2, S-11) were given to genetically susceptible S-strain or P-line birds with or without immunosuppressive treatments. Based on lesion incidence and type during an 8-10-week experimental period, embryonal (17-day) bursectomy and neonatal cyclophosphamide (CY) treatment were without effect on CU-1 and CU-2 infections in P-lines. S-11 virus was virulent for P-lines, and CY treatment reduced MD incidence as reported by others for virulent virus infections. Neonatal thymectomy or infection in ovo (at 8 days of incubation) or use of the more susceptible S-strain chicks all increased the incidence of MD induced by CU-1 and CU-2 viruses. It was concluded that the "low virulence" of these viruses is a reflection of an adequate immune response by the host.

Changes in polymorphic gene frequencies in strains of chickens selected for resistance to Marek's disease

Resistance to Marek's disease (MD) was selected over five generations in three strains and their four substrains. 2. MD mortality decreased consistently on natural exposure, but in birds artificially inoculated the mortality increased again in later generations. 3. Changes of gene frequencies at five polymorphic loci--blood group A, B and D, plasma esterase and alkaline phosphatase loci--were examined. 4. The frequencies of blood group A6 and B8 alleles showed a consistent trend of increase and the B11 allele gradually decreased in most strains. The Akp allele of alkaline phosphatase increased significantly in two of seven strains. 5. Comparisons of homozygotes and heterozygotes revealed a significant difference only at the A locus.

Genetic resistance to lymphoid tumor transplants

Day-old chicks of Ottawa strains 4 and 5 and Cornell strains K and S, with or without maternal antibody against antigens related to Marek's disease (MD), were challenged with serial dilutions of MD tumor transplants (JMV-L or JMV-H) or transmissible lymphoid tumor (TLT) of Olson in three consecutive experiments. Thirty chicks were tested in most combinations of strain, dilution and antibody status for a total of approximately 2000 chicks per experiment. Two subsequent experiments, with a total of more than 1900 chickens, investigated the influence of age at challenge on the resistance of strains 4, K and S to JMV-L and the objective of the sixth experiment was to determine the chromosomal sex of the tumor cells. In terms of mortality up to 16 or 17 days after inoculation, the response to challenge of day-old chicks with JMV-L did not appear to be influenced by the presence of antibody against MD related antigens but differed among strains of chickens. The estimated dose (LD50) that would kill 50% of a challenged population of Strain 4 was approximately 10,000 live JMV-L cells, while the corresponding estimates for strains 5 and K were approximately 600 cells and for strain S it was 50 cells. JMV-H and TLT were highly lethal to all four strains and all estimates of LD50 at 16 or 17 days post challenge were less than 10 cells. Resistance to JMV-L increased rapidly with age at challenge. Strains 4 and K were approaching complete resistance by 7 days of age and the susceptible strain S, when challenged at 14 days, was more resistant than day-old chicks of strains 4 and K. The chromosomal sex of the JMV-L, JMV-H and TLT tumor cells was female and this marker was used to confirm their transplantability.

Chromosomal characteristics of six cultured lymphoblastoid cell lines originating from Marek's disease lymphomas

Cytogenetic observations were made on 6 cell lines (MOB-1, MOB-2, MOB-3, MSB-1, HPRS Line 1, HPRS Line2) originating from Marek's disease lymphomas and 2 clones (1104-B, 1104-X-5) of a cell line established from an avian lymphoid leukosis tumor. The modal chromosome number was within the diploid range in all the lines except HPRS Line 1 and HPRS Line 2, both of which had a mode at about 60. Karyotypes were grossly abnormal in 4 cell lines: trisomy for No. 1 in MOB-2; the heteromorphic No. 1 pair in MSB-1, and marker chromosomes derived from rearrangements involving No. 3 or No. 5 and unidentified elements in HPRS Lines 1 and 2. The MOB-1 line which had been characterized by cells with an apparently normal karyotype was completely taken over by cells with a heteromorphic No. 1 pair morphologically similar to the one found in MSB-1 by the 95th day of continuous growth in vitro. BUdR-acridine orange differential staining technique revealed, however, different banding patterns in these abnormal chromosomes.

Marek's disease: effects of B histocompatibility alloalleles in resistant and susceptible chicken lines

Lines of chickens selected from a common ancestral population for either resistance or susceptibility to Marek's disease developed contrasting frequencies of particular B alloalleles. Comparison of inoculated sibs in backcross-families revealed that the B alloalleles characterizing the two lines accounted for an eightfold difference in tumor incidence. This genetic difference in tumorigenesis associated with the alloalleles of the major histocompatibility complex is probably expressed through the cell-mediated immune system.

Role of the major histocompatibility complex in resistance to Marek's disease: restriction of the growth of JMV-MD tumor cells in genetically resistant birds

B21 is associated with resistance to Marek's disease (MD). Forty populations of chickens from all over the world were examined for the presence of the B21 allele. B21 was found in twelve of these populations and it's presence was confirmed by GVH testing in all ten populations which were tested. The populations in which B21 was detected represent the extreme production types of the species and include the progenitor of the species, the Red Jungle Fowl. Our studies suggest that B21 may have strong survival value for the species. An allogeneic transplantable lymphoma of MD, the JMV tumor cell line, grows more slowly in MD resistant (B21/B21) chicks than in MD susceptible (B2/B2) chicks. This is the first direct evidence that genetic resistance to MD may involve an active (immunological?) restriction of tumor cell growth. JMV cells were further characterized as a transplant of B1 carrying lymphoblastoid cells, an allele which may be associated with susceptibility to MD.

Genetic resistance to Marek's disease

A programme to control MD by genetic selection was tested by selecting breeding sires and dams whose progeny were found to have above average resistance to MD following inoculation at day old with infectious material. Under conditions of natural exposure, Australorp pullets from parents selected for resistance had a lower incidence of MD lesions than an unselected Australorp group. In experimentally challenged Australorp chickens the incidence of MD was significantly lower in progeny derived from mating resistant Australorp sires with unselected dams than in progeny from an unselected Australorp line. Under conditions of experimental and natural exposure to MD, crossbred chickens derived from resistant White Leghorn sires and Australorp dams had a lower incidence of MD lesions than the chickens derived from susceptible White Leghorn series and unselected Australorp dams.

Studies on genetic and vaccination-induced resistance of chickens to lymphoid tumor transplants. 1. Marek's disease tumor transplant (JMV)

Six strains and 4 inbred lines of chickens that differed in susceptibility to Marek's disease (MD) were inoculated in the wing web with JMV when 5 weeks old. Wing web tumors (WWT) developed in all strains and lines inoculated with low-passage JMV (JMV-L) but were largest in Cornell Strain S (highly susceptible to MD). Of 3 strains inoculated with high-passage JMV (JMV-H), only Strain S had appreciable WWT development. Seventy-five percent of the unvaccinated S strain chickens challenged with JMV-L or JMV-H died during the experiments, and approximately half of this mortality occurred during the second week postinoculation. Inbred Line GC ranked next in susceptibility to Strain S and was more susceptible than other lines and strains, including the strain from which it originated. Vaccination with turkey herpesvirus one week before challenge protected against mortality and suppressed WWT development. The effect on WWT development was less, however, in Strains S and NH than in other strains. The transplantability of the tumor was investigated with the use of sex chromosomes as cell markers. Five to 7 days postinoculation of male Strain S chicks with JMV-L or JMV-H, most cells in metaphase from wing web or visceral tumors were of female origin. By 56 days, only male cells were found in visceral tumors. The interpretation was that early lesions were due to tumor transplantation and later lesions were induced by virus.

Natural resistance to Marek's disease at hatching in chickens lacking maternal antibody, and relationship between this early resistance and resistance acquired with age

Chickens of lines 6 and N, selected for resistance to Marek's disease (MD) and lacking maternal antibody, were resistant to MD mortality when exposed to pathogenic MD virus (MDV) at 1 day old. This finding indicated that natural resistance to MD is well developed at hatching in certain lines and is not dependent upon increasing age. Evidence obtained for lesion regression in early resistance and for possible genetic control of resistance acquired with age indicated that resistance at hatching and that acquired with age may be similar in character and may represent early and late manifestations of common natural resistance, possibly mediated through similar mechanisms.

Rous sarcoma regression in chickens resistant or susceptible to Marek's disease

In 4 experiments, strains of chickens relatively susceptible (S-strain, P-line) or resistant (N-line, PDRC) to Marek's disease (MD) were challenged with Rous sarcoma virus (RSV) at 6-8 weeks old. RSV tumors occurred in 94-100% of the birds in each strain, but the number with tumors that regressed during the 40-46-day experiment varied from 7% (S-strain) to 91% (PDRC). The N-line and P-line birds, derived from a random-bred flock with selection only for susceptibility or resistance to MD, regressed their tumors at about equal rates (respectively 59 and 65%). Thus, although the genetic strains differed in ability to regress RSV tumors, the difference was not necessarily related to genetic resistance or susceptibility to MD. Other birds in 2 of the experiments, infected 2-4 weeks earlier with JM or GA isolants of MD virus, had significantly (P less than 0.01) lower incidence of RSV tumor regression than did controls provided that they developed gross lesions of MD.

Effects of strain of chickens and vaccination with turkey herpesvirus on Marek's disease and lymphoid leukosis in breeding stocks

1. A total of 3236 females from eight meat-type strains, half of which were vaccinated for Marek's disease (MD), and 11,193 Leghorn females from ten strains, all vaccinated for MD, were adventitiously exposed to MD and lymphoid leukosis (LL) viruses and observed to 392 and 497 d of age, respectively. 2. In the meat-type birds, vaccination reduced total mortality from 43-4% to 27-1% and mortality due to MD from 16-4% to 5-4% but did not affect mortality and LL (2-9% and 3-4%). 3. In the vaccinated Leghorns total mortality was 11%, including 2-1% from MD and 1-2% from LL. 4. Significant differences between strains of chickens were found in total mortality, as well as in MD and LL mortality. 5. Strain by vaccination interaction was observed in total rearing and adult mortality, as well as in the MD mortality of adult meat-type females. 6. Leghorn strains with higher rate of egg production and meat-type strains with lower growth rate to have better viability.

Two levels of genetic resistance to lymphoid leukosis

Two levels of genetic resistance to lymphoid leukosis are recognized: 1) cellular resistance to virus infection; and 2) resistance to tumor development in leukosis-virus-infected birds. Resistance to infection is simply inherited but is very specific for the subgroup of virus. Inheritance of resistance to tumor development is more complex but appears to be less subgroup-specific. A breeder may wish to select for resistance to infection of virus eradication is the goal. If his goal is the reduction of lymphoid tumors, with virus infection not important, he may choose to select for resistance to tumor development.

Imidazole in organs of inbred chickens selected for resistance or susceptibility to lymphoid leukosis or Marek's disease

Total and soluble imidazole was determined on samples of liver and kidney and soluble imidazole was determined on blood from eight strains of chickens selected at three locations for resistance or susceptibility to lymphoid leukosis and/or Marek's disease. Liver and kidney total and soluble imidazole was not different between strains classed as resistant or susceptible to lymphoid leukosis and/or Marek's disease. The weighted average of soluble blood imidazole was higher (P smaller than 0.01) in strains classed as resistant to lymphoid leukosis. A similar difference (P smaller than 0.01) was observed with strains classed as resistant or susceptible to Marek's disease when the selections from one location were not included in the weighted average.

Antibody response of genetically susceptible and resistant chickens to cell-free and attenuated JM-V leukosis strain and its influence on early type II (Marek's) leukosis infection

Experiments were carried out to: 1) determine the antibody response of chickens to cell-free and attenuated preparations of JMV leukosis strain, 2) determine the differences in antibody response to these antigens between susceptible (P-line) and resistant (N-line) chickens by means of serum neutralization and indirect fluorescent antibody tests, 3) investigate the influence of maternal (passive) antibody on early (day-old) JMV vaccination and 4) investigate the influence of maternal antibody in chicks naturally exposed continuously to JM virus from day-old to 8 weeks of age on the pathogenesis of Type II leudosis (Marek's) infections and oncogenesis.

Viremic responses of genetically susceptible and resistant chickens to experimental infection with acute, mild, or both strains of Marek's disease herpesvirus

The development and persistence of viremia were followed in two lines of Single-Comb White Leghorns: one experimental line (WSU-VS) highly susceptible, and one commercial line (C-WL) relatively resistant to Marek's disease(MD). In the resistant C-WL chicken, viremia with a mild strain of MD herpesvirus (MDHV) persisted in all viremic birds through 8 weeks postinoculation (PI), while viremia with an acute strain of MDHV did not, resulting in a decrease in number of viremic birds after 2 weeks PI. In the susceptible WSU-VS chicken, viremia with acute MDHV persisted in all viremic birds whereas viremia with mild MDHV was detected in a decreasing number of birds after 6 weeks PI. The pattern of viremia observed in the dually infected groups simulated a combination of the responses of the two groups respectively inoculated with mild and acute MDHV. Whether inoculation was with acute MDHV alone, or together with mild MDHV, levels of viremia with acute MDHV were appreciably higher in the WSU-VS than in the C-WL chicken. In both lines, levels of viremia were higher with acute MDHV than with mild MDHV but viremia with acute MDHV could not be demonstrated in the C-WL bird at 6-8 weeks PI. Levels of viremia with mild MDHV were consistently and similarly low in both WSU-VS and C-WL chickens.