The lymphocyte transformation assay was used to monitor the cellular immune response of rabbits sensitized to cytomegalovirus (CMV). Peripheral blood lymphocytes from animals inoculated with purified virus were specifically stimulated by crude or twice-banded CMV. Blood cells from rabbits immunized to herpes simplex virus type 1 (HSV-1) responded to that antigen but not to CMV. Viable or heated CMV preparations stimulated unwashed blood cells as efficiently as washed cells. Furthermore, preincubation of stimulating antigen with anti-CMV serum did not prevent lymphocyte activation. Lymphoid cells readily stimulated by virus antigen were not stimulated by cells transformed by CMV or HSV-1.
The nature of the host's immune response to isografts of hamster embryo fibroblasts (HEF) transformed by herpes simplex virus type 1 (HSV-1) was investigated by the microcytotoxicity assay. It was found that spleen cells from tumor-bearing hamsters killed homologous tumor cells but not HEF transformed by cytomegalovirus or PARA-(defective SV40)-adenovirus 7 (PARA-7). Cytotoxicity was lost as the tumor increased in size. Spleen cells from animals bearing isografts of HSV type 2 (HSV-2) transformed cells also killed HSV-1 target cells whereas spleen cells from PARA-7 tumor bearers did not. Further studies showed that animals immunized with HSV-1 or HSV-1-infected rabbit kidney cells produced spleen cells specifically cytotoxic for HSV-transformed cells. On the other hand, sera from virus-immunized hosts or tumor bearers had no effect on the cells in the presence of guinea pig complement. However, in blocking experiments such sera could significantly reduce spleen cell cytotoxicity.
These experiments established that cells transformed by HSV could elicit a cellular immune response in the syngeneic host, and provided evidence that the immunity was directed against virus-specific antigens on the cell surface.
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