| Popis: |
The leukosis/sarcoma viruses, members of the avian oncornavirus or oncovirus group, cause a wide spectrum of tumors in chickens. The most common under field conditions is lymphoid leukosis, a B-cell lymphoma. In susceptible chickens infected at an early age, cells of the cortex of the bursa of Fabricius of 6- to 8-week-old chickens transform and proliferate until the whole follicle is filled with transformed lymphoblasts. At about sexual maturity (18 to 20 weeks) the cells in some bursa follicles burst into the blood vessels and metastasize to other organs causing death. In other follicles the incipient tumors regress. Regression is likely enhanced by testosterone, and inhibited by the immunosuppressive effect of the virus and the tumor. Immune response genes may play a role. Resistance to tumor development in chickens susceptible to infection but genetically resistant to tumor formation could be mediated through regression of in situ tumors. |
