Effect of selection for resistance and susceptibility to viral diseases on concentrations of dopamine and immunological parameters in six-week-old chickens.

White Leghorn chickens were inbred respectively from their parent lines, which were diversely selected for resistance (line 6(3)) or susceptibility (lines 7(2) and 15I(5)) to Marek's disease and lymphoid leukosis. The differences in disease resistance may have been due to differential regulation of immune and neuroendocrine homeostasis. At 5 wk of age, chickens from the same line were randomly assigned to cages at 4 birds per cage. Blood samples were collected from the chickens at 6 wk of age (n = 10/line). Subsets of T lymphocytes (CD4+ and CD8+) and B cells were measured using flow cytometry. Concentrations of plasma IgG and dopamine were quantified with ELISA and HPLC assay, respectively. Line 6(3) chickens had a higher percentage of CD8+ cells but not CD4+ cells than the chickens of the lines 7(2) and 15I(5) (P < 0.01). In contrast, both lines 7(2) and 15I(5) had a greater percentage of B cells (P < 0.01). The concentrations of plasma IgG and dopamine were also regulated differently among the lines; both were in an order of 7(2) > 15I(5) > 6(3) (P < 0.05 and P < 0.01, respectively). These results suggested that genetic selection for disease resistance also directly or indirectly modified the corresponding genetic components that govern the immune and neuroendocrine systems. The genetic lines of chickens may be used as animal models for investigation of the cellular mechanisms of genetic-environmental interactions on disease resistance.