Influence of B complex versus non B genetic background on cellular resistance and on Rous Sarcoma virus‐induced tumour regression in chickens1

Differential resistance to Staphylococcus aureus challenge in major histocompatibility (B) complex congenic lines

Ten inbred B-congenic Leghorn lines were challenged with two isolates of Staphylococcus aureus at 3 days and 6 wk of age. Significant differences in mortality were observed among such lines when challenged at 3 days with either S. aureus Isolate P4L (moderately pathogenic) or S. aureus Isolate 3727 (highly pathogenic). Line 331 (B2/B2 genotype) had lower mortality than either Line 004 (B17/B17, chi 2 = 4.13, P < .05) or Line 253 (B18/B18, chi 2 = 4.23, P < .05) challenged with Isolate P4L. The use of a susceptibility index allowed for the detection of additional differences among the various lines challenged by Isolate 3727. Line 336 (BQ/BQ) was more resistant than either Line 335 (B19/B19, P < .01) or Line 330 (B21/B21, P < .01). No significant differences were found among the lines challenged at 6 wk by either isolate. The results provide additional evidence for the importance of the B complex in genetically determined disease resistance, and further demonstrate the usefulness of congenic lines in such investigations.

Influence of the major histocompatibility complex on tumor regression and immunity in chickens

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.

Estimates of heritability of response to Rous sarcomas of chickens

The stocks used for this investigation consisted of 1039 F3 generation progeny from the cross of two highly inbred lines and 355 and 462 offspring from subpopulations UNH 105A and UNH 105B, respectively, of a noninbred line of New Hampshires. Matings were such that B complex alleles were segregated in the three experimental populations with minor exceptions. Each chicken was inoculated at 6 weeks of age with a subgroup of Rous sarcoma virus (RSV). Resulting tumors were subjectively scored on a scale from 0 (no tumor) to 6 (massive tumor) six times during a 10-week experimental period. Based upon the six tumor scores, each chicken was then assigned a tumor profile index (TPI), a criterion of antitumor response. The TPI were analyzed by least squares analysis of variance and corrected for hatch, sex, and virus prior to obtaining components of variance and estimates of heritability from a nested analysis of variance. Estimates of heritability from the sire component ranged from 0 to .41 +/- .27 and from the dam component .18 +/- .09 to .26 +/- .14, which are rather low estimates in general.