Subgroup J avian leukosis virus-induced histiocytic sarcomatosis occurs only in persistently viremic but not immunotolerized meat-type chickens.

The role of subgroup J avian leukosis virus (ALV J) infection profile in the development of histiocytic sarcomatosis (HS) in chickens was evaluated using retrospective analysis of 2 experiments involving in ovo and at-hatch inoculation of commercial meat-type and ADOL line 0 chickens with 100 or 10,000 TCID(50) of various strains ALV J. HS was observed only in persistently viremic, meat-type chickens that were inoculated at hatch, but not in immunotolerized (persistently viremic, with no antibodies), in ovo inoculated chickens. However, the immunotolerized, in ovo inoculated chickens developed a high incidence of myeloid tumors. HS appeared to arise from the splenic ellipsoids and red pulp, and metastasized to liver, kidney, and other organs. The neoplastic cells were diffusely positive for ChL5, CD45, and MHC class II with multifocal infiltration of T and B lymphocytes. Expression of viral antigen gp85 within HS was very low compared with that noted in ALV J-induced myelocytomas. The above observations suggest that the mechanisms of oncogenesis of HS might be different from that of other ALV J-induced tumors.