Differences in pathogenicity among ALV strains of the same or different subgroup
Résumé
Abstract. An efficient induction of the wasting disease in chickens by avian leukosis virus (ALV), particularly ALV subgroup C, requires >102 IU of virus inoculated in mid embryogenesis. The most conspicuous symptoms of the disease were induced by ALVs subgroup C; however, significant differences in the occurence of wasting disease were found among individual members of this subgroup. Almost comparable pathogenicity was exhibited by ALVs subgroup D, whereas viruses of subgroups B and A proved to be moderately and almost non- pathogenic, respectively. Using antibodies to cellular antigens, tissue alterations were shown clearly in ALV-C-infected chickens. An essential feature was depletion of lymphocytes in the thymus, bursa and spleen. While the number of dendritic cells (DC) in the bursa was increased, their representation in the thymus and spleen was reduced. In the spleen, however, the reduction of DC concerned only an ellipsoid compartment, which in itself was also markedly reduced. An increased number of macrophages in the thymus and spleen corresponded with the observed general activation of the monocyte-macrophage system. In the spleen CD4+ T-cells were reduced while CD8+ T-cells were increased. In agreement with this finding was a failure of chickens to respond to Brucella antigen and inability of their splenocytes to respond to ConA, both of which pointed to the damage of immune reactivity. Variation in the pathogenicity among individual ALV strains provides ground for depicting gene sequences playing an important role in ALV acute pathogenicity.
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