SUMMARYThe efficiency of the transfection of chicken fibroblasts with a single dose (I"5 to I5O #g) of DNA isolated from virogenic RSV (Prague strain)transformed XC cells was increased if chicken fibroblasts were pre-treated with BUdR. Mitomycin or u.v. irradiation in doses used were not efficient. The repeated attempts to transfect duck fibroblasts, not containing activable endogenous chicken virus genome or group-specific antigen, always failed.Both DNA isolated from purified nuclei and whole virogenic cells exerted the same transfecting activity.Transfecting activity was present in the peak fractions obtained after CsC1 gradient sedimentation of DNA obtained from virogenic cells, was absent in RNA preparations and after digestion of DNA with DNase or alkaline denaturation. This indicates that DNA is responsible for transfection. The role of endogenous virus genomes in transfection is discussed.
Tissue grafts from a histoincompatible donor of the same developmental stage were introduced into an early chick embryo host in order to probe the immune response to the graft after birth, when the host has reached immune maturity. Limb buds from B4 or B12 chicken strains were grafted in situ on (B15 x B21)F1 recipients that were allowed to hatch. The grafted wing grew normally and was tolerated in a nearly perfect way during the host's lifetime, although reversible rejection crises severely affected the fundamentally healthy state of the grafted tissues. Skin grafts of the same major histocompatibility complex haplotype as the wing were performed on the adult wing-chimera and were permanently tolerated. In contrast, host peripheral blood lymphocytes maintained their capacity to proliferate against donor cells in the mixed lymphocyte reaction. These results, while showing that in vitro and in vivo tolerance are separable phenomena, suggest the existence of a peripheral mechanism inducing tolerance to self that complements the elimination of self-reactive clones by the thymus.
Using a method of cocultivation of embryonic Chinese hamster cells (CHEF) with Rous sarcoma cells and infection of CHEF by RSV-SR, it was possible to obtain malignant transformation of hamster cells. The morphologically altered cells became apparent within 15-36 days.In the cells transformed by cocultivation, the genome of RSV was determined by the method of contact of the transformed cell and the chicken cell in vivo; the malignant character of the transformed cells was demonstrated by transfer to a homologous newborn host. Repeated attempts to detect virus production in transformed Chinese hamster cells failed.Prior to malignant transformation and in early transformed cultures the diploid stem-line was maintained. A slight decrease in the proportion of diploid cells in transformed cultures was revealed i n some experiments and is discussed. Prolonged cultivation of these cells, as also of control fibroblasts, shifts the stem-line to the hyperdiploid or hypotetraploid region.The mechanism of malignant transformation by RSV i s discussed with regard to the action of the viral genome and alteration of the genetic make-up of the cell by the virus.
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