Suppressor mechanisms in neonatally acquired tolerance to a Gross virus-induced lymphoma in rats

Tolerance to a highly immunogenic Gross virus-induced tumour in Wistar/Furth rats (C58NT)D was produced by neonatal infection of the rats with the virus. These rats failed to reject the tumours when challenged 8 weeks after virus inoculation and to mount the appropriate cell-mediated immune response to the tumour. The mechanisms involved were studied in vivo by adoptive transfers into sub-lethally irradiated rats of tumour cells mixed with spleen cells and/or sera from normal, tolerant, or tumour immune rats, and in vitro by a 51Cr release assay involving similar mixtures. The results indicate the presence of a suppression mechanism which is sensitive to irradiation and abolished by trypsinisation. Weak blocking factors can also be detected in serum. An interpretation in terms of the release of virion proteins from infected cells is proposed, although participation of suppressor lymphocytes has not been excluded.