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From circulating immune complexes (ICs) of BLV-infected cattle, an antigen preparation was produced that contained some virus-specific proteins and a tumour-associated antigen. Eleven hybridoma clones were produced that secreted monoclonal antibodies (MoAbs) to this tumour-associated antigen, and two of them, MoAbs 1B4 and 1E9, were used in further studies. Most antibodies were of IgG1 subclass and showed no cytotoxic activity towards lymphocytes of BLV-positive cattle or to certain tumour cells. The MoAbs 1B4 and 1E9 recognized an antigen of about 75 kD on the cell surface of bovine lymphosarcoma cells and circulating lymphocytes from BLV-infected cattle with persistent lymphocytosis. The results presented indicate that the circulating immune complexes from BLV-positive cattle contain a tumour-associated antigen that is expressed on tumour cells and on lymphocytes from cattle with persistent lymphocytosis.

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Two hybridoma clones have been produced by hybridization of murine myeloma cell line PAI and splenocytes from BALB/c mice immunized with cells from a transplantable sarcoma induced in rat by SR-RSV. The antibody produced by hybridoma clone 2C2 was of subclass IgG3 and recognized a cell surface antigen of 52 kD. It only cross-reacted with cells from SR-RSV-induced sarcoma in hamster, but not with cells from the chicken RSV-induced sarcoma, nor with a number of methylcholanthrene sarcomas and various other tumors of viral or other etiology developed in rats, mouse, hamsters or chickens. The antibody produced by hybridoma clone 5G2 was of subclass IgG2A and recognized an antigen of 28 kD which was located under the plasma membrane, particularly in the cell protrusions and microvilli. Cross-reactions were found with all sarcoma cells tested, indicating that this antigen might represent a common sarcoma antigen of comparatively low molecular mass.

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The pathogenicity of avian myelocytomatosis virus MC29 was studied in F1 hybrids of two Prague inbred lines of chickens-CC xIA (B4/B7 genotype) and CB x IA (B12/B7 genotype). A shorter latent period and a higher mortality was found in the CC x IA chickens. In most chickens of this group, subperiosteal accumulations of primitive cells on the ribs, sternum and pelvic bones were observed, which were never detected in the CB x IA chickens. Unlike the typical myelocytomatosis, however, most of these cells were without specific cytoplasmic granules which indicated that they were less differentiated than the myelocytes. Another unexpected finding was the severe leukemia which developed in most CC x IA chickens, the primitive cells in the peripheral circulation having the typical morphology of myeloblasts. Tumour growths in the proventriculus were observed for the first time in both experimental groups of chickens. Lymphoid leukosis of a short latency was found in two CB x IA chickens. Of particular interest is the demonstrated severe selective suppression of myelopoiesis in the bone marrow of two CC x IA chickens as this is quite opposite to the usual activity of virus MC29. The results presented indicate that the pathogenic and oncogenic effects of virus MC29 depend on host genetic factors and that after infection of some inbred line of chickens, the myeloid cell differentiation might be arrested at various levels, including at the myeloblast stage.

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The presence of protein A in the stable L-form of S. aureus BM 3041 was proved. Its amino acid composition and electrophoretic characteristics were compared with the parent strain. The location of protein A on the cytoplasmic membranes of the L-form cells, as well as on the extracellular membranes were established by immunoelectron microscopy. In the cells of the parent bacterium its location on the cell wall was observed.

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Whole histone was isolated from the immature cells of the peripheral blood of White Leghorn chickens, line 151, with leukosis experimentally induced by avian leukosis virus, strain E26 (ALV-E26). Histone H5 was demonstrated in all samples of these cells and was characterized by electrophoresis in polyacrylamide gel, extraction with perchloric acid, amino acid analysis, and immunodiffusion in agarose gel. Histone H5 was not detected in the myeloblasts of chickens with myeloblastosis caused by the avian myeloblastosis virus. It was concluded that the immature cells (IBC-E26) obtained from the peripheral blood of chickens responding positively to ALV-E26 belonged to the erythroid blood cell series and that ALV-E26 induced in vivo erythroblastosis but not myeloblastosis in chickens. The relative amount of histone H5 in IBC-E26 was two times higher than that in the erythroblasts obtained from the peripheral blood of chickens with erythroblastosis caused by avian erythroblastosis virus, strain R of Engelbreth-Holm. Thus the erythroblasts in the circulating blood of chickens with leukosis induced by ALV-E26 seemed to be more differentiated.

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