PATHOGENICITY OF AVIAN MYELOCYTOMATOSIS VIRUS MC29 IN 2 LINES OF CHICKENS

The pathogenicity of avian myelocytomatosis virus MC29 was studied in F1 hybrids of two Prague inbred lines of chickens-CC x IA (B4/B-7 geno type) and CB x IA (B-12/B-7 genotype). A shorter latent period and a h igher mortality was found in the CC x IA chickens. In most chickens of this group, subperiosteal accumulations of primitive cells on the rib s, sternum and pelvic bones were observed, which were never detected i n the CB x IA chickens. Unlike the typical myelocytomatosis, however, most of these cells were without specific cytoplasmic granules which i ndicated that they were less differentiated than the myelocytes. Anoth er unexpected finding was the severe leukemia which developed in most CC x IA chickens, the primitive cells in the peripheral circulation ha ving the typical morphology of myeloblasts. Tumour growths in the prov entriculus were observed for the first time in both experimental group s of chickens. Lymphoid leukosis of a short latency was found in two C B x IA chickens. Of particular interest is the demonstrated severe sel ective suppression of myelopoiesis in the bone marrow of two CC x IA c hickens as this is quite opposite to the usual activity of virus MC29. The results presented indicate that the pathogenic and oncogenic effe cts of virus MC29 depend on host genetic factors and that after infect ion of some inbred line of chickens, the myeloid cell differentiation might be arrested at various levels, including at the myeloblast stage .