The critical time of avian leukosis virus subgroup J (ALV-J)-mediated immunosuppression was determined by body weight, relative immune organ weight, histopathology, and presence of group specific antigen and antibodies in specific pathogen-free (SPF) chickens. CD4+ and CD8+ cell activity in the spleen, total and differential leukocyte counts in blood, and viral RNA levels in spleen were measured. Significant growth suppression was observed in the two ALV-J-infected groups. A strong immune response by infected groups was present in spleen at 2-weeks-of-age, but after 4-weeks-of-age, the response decreased quickly. The thymus and bursa showed persistent immunosuppression until 4-weeks-of-age. Proliferation of fibroblasts and dendritic cells were observed in immune organs at 4- and 5-weeks-of-age. However, the granulocyte cell number was markedly lower in the infected groups than in the control group. In group 1 (day 1 infection) CD4+ cells increased during the second week but significantly decreased during the fourth week, while group 2 (day 7 infection) showed the opposite effect. Viral RNA increased significantly by the fourth week. These data identify 3~4 weeks post-infection as the key time at which the ALV-J virus exerts its immunosuppressive effects on the host.
Animals ; Antibodies, Viral/blood ; Antigens, CD4/blood ; Antigens, CD8/blood ; Avian Leukosis/*immunology/transmission/virology ; Avian leukosis virus/classification/*immunology ; Body Weight ; *Chickens ; China ; Enzyme-Linked Immunosorbent Assay/veterinary ; Immune Tolerance ; Leukocyte Count/veterinary ; Poultry Diseases/*immunology/transmission/virology ; RNA, Viral/genetics ; Real-Time Polymerase Chain Reaction/veterinary ; Reverse Transcriptase Polymerase Chain Reaction/veterinary ; Specific Pathogen-Free Organisms ; Spleen/immunology