Antigenic Behavior of the S-63 Mouse Leukemia Virus

The present studies are an extension of earlier reports on the antibody response of mice to a leukemogenic virus (S-63). These investigations were designed to show whether a correlation exists between in vivo and in vitro determinations, and whether protective antibodies against the virus could be produced in immune-tolerant animals. Viral neutralization and protection studies in mice were compared with passive cutaneous anaphylaxis (PCA), immunodiffusion, microprecipitin, and immunofluorescent tests using similar antigens and antibodies. As shown in tables 1, 2 and 3, antibody could be demonstrated by both in vivo and in vitro methods, and these studies showed (table 2) that the antibody was protective.

The S-63 leukemia virus was isolated in 1963 from a mouse ascites cell leukemia line. That cell line had been carried in the laboratory for over 3 years. The virus has been carried in ICR mice since its isolation. Immunologic studies were carried out to determine the relation between the virus and the originating ascites cell. Studies of antibodies produced in normal rabbits against the S-63 virus were unsatisfactory for purposes of these experiments because of cross reaction with normal mouse tissue. Immune-tolerant animals have yielded valuable information:

Antibodies produced in immune-tolerant rabbits injected with the S-63 virus do not cross react against intact ascites cells from which the virus was originally isolated. Conversely, antibodies similarly produced against the ascites cells do not react against the virus antigen.

Antibodies produced in immune-tolerant rabbits against ascites cells protect mice against ascites cell-induced leukemia, but not against the disease induced by S-63 virus. Mice challenged with ascites cells and treated with antiascites cell gamma globulin are protected against the disease. The best therapeutic advantage is obtained when treatment is started either at the time of cell inoculation or in the early stages of the disease.

Antibodies which protect newborn animals from infection develop in adult ICR mice recovering from S-63 virus leukemia. These antibodies produced by convalescent mice are similar, from the standpoint of protection, to those produced in immune-tolerant rabbits.