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.