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A number of studies show that major histocompatibility complex (MHC) genes control host immune responses to viral-induced chicken tumors. The MHC gene-controlled responses to malignant neoplasms caused by Rous sarcoma virus, lymphoid leukosis virus and Marek's disease virus are reviewed. Genes that determine regression of Rous sarcomas and resistance to development of lethal Marek's disease lymphomas appear to map within the B-F region of the MHC. In some cases, genetic complementation of both MHC genes and non-MHC genes may be responsible for regression of tumors. Metastasis of Rous sarcoma cells is also influenced by the host's MHC genotype. Background genes can modify the specific MHC gene effect on resistance to progressive growth of Rous sarcomas and Marek's disease lymphomas. Studies showing that MHC-restricted immunity may be important in cytotoxic T cell reactions to virus-infected and/or transformed chicken cells are discussed. The MHC-restricted cytotoxicity, whereby the T cells and target cells must share one MHC haplotype for in vitro killing to occur, suggests that the T cells have receptors that recognize virus-altered self MHC antigens. This may be an important immune surveillance mechanism for limiting the proliferative growth of virus-induced tumors in chickens.

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