Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2006
Publication Date: 5/1/2006
Citation: Zhang, H.M., Hunt, H.D., Kulkarni, G.B., Palmquist, D.E., Bacon, L.D. 2006. Lymphoid organ size varies among inbred lines 63, 72 and their thirteen recombinant congenic strains of chickens with the same major histocompatibility complex. Poultry Science. 85:844-853. Interpretive Summary: To explore genetic makeup that determines disease resistance in one inbred line of animals and disease susceptibility in another, the two inbred lines are crossed and backcrossed to produce new lines of animals which provide unique utility in genetic research. These new lines of animal are called recombinant congenic strains of animals. This is a powerful approach for identifying and mapping genes that influence cancer-like diseases known as tumors. The strength of this approach lies in the extent of genetic and phenotypic (measurable) characterization of a series of strains of such animals. This study, as part of a phenotypic characterization endeavor, reports the phenotypic variability of lymphoid organ sizes of a series of recombinant congenic strains of chickens and their inbred parental lines developed and maintained at Avian Disease and Oncology Laboratory, East Lansing, Michigan. Relative bursa, thymus, and spleen sizes were examined in two experiments. The differences of average relative bursa size, thymus size, bursa/thymus ratio, and spleen size among the inbred parental lines and thirteen recombinant congenic strains were statistically very significant. Since at least two kinds of important lymphocytes (B-cells and T-cells), which are responsible for antibody response and cell-mediated immune functions respectively, develop and mature in bursa and thymus, identification of genetic factors controlling the sizes of lymphoid organs may lead to new understanding of roles these genetic factors might play in influencing important biological functions involved in antibody and immune responses to disease susceptibility.
Technical Abstract: The objective was to evaluate lymphoid organ size in chickens from a series of thirteen recombinant congenic strains (RCS) and their highly inbred parental lines (63 and 72). The parental line 63 was selected for resistance to tumors induced by Marek’s disease virus and avian leukosis viruses, whereas line 72 was selected for susceptibility to these tumors. Each RCS on the average contains a random 1/8 of genome from the donor line 72. Previous studies have shown that lines 63 and 72 differ in the size of primary lymphoid organs; i.e., the bursa of Fabricius and the lobes of the thymus are smaller in line 63 than line 72. In this study the relative size of the thymus, bursa of Fabricius, and spleen was first examined in about 15 males from each of thirteen RCS and the two parental lines at 61-69 days of age. The differences of relative bursa, thymus and spleen size among the RCS and the parental lines 63 and 72 differed significantly (P <0.001). Males and females from four RCS and the two parental lines were evaluated a second time and differences in the relative sizes in lymphoid organs among the RCS and parental lines were consistent. In two RCS the size of the T and BF was comparatively large as in line 72, leading to the conclusion that different allelic forms at one or more loci in these RCS regulate the size of both organs. In two other RCS the BF was large compared to the thymus, suggesting that allelic forms at some loci in these RCS influence the BF independent of the T. The relative lymphoid organ size among the RCS appeared to co-segregate with the concentration of immunoglobulin G in the plasma measured previously. The evaluation of genomic variability of these lines is underway, and the RCS are available for research on traits that differ between lines 63 and 72.