The immunomodulatory effects of clonidine, an alpha-2-adrenergic agonist, in laying hens

The ability of the sympathetic nervous system to regulate chicken immune function was examined. Clonidine, an alpha-2 adrenergic receptor agonist, was administrated at 2.5, 5.0, or 10.0 mg/L in the drinking water of White Leghorn hens at 48 wk of age. The hens were randomly housed in conventional cages in pairs. Concentrations of plasma IgG (also named IgY) were detected using chicken IgG ELISA, and the percentage of subpopulations of circulating lymphocytes were analyzed using flow cytometry. Compared with controls, treated hens had higher circulating IgG levels and a greater percentage of circulating B cells (Bu-1+ cells, P < 0.01) after 1 wk of treatment. Additionally, the percentages of CD8+ cells were consistently higher (P = 0.07) in the treated hens compared with controls, whereas the percentages of CD4+ cells and the ratio of CD4+ cell to CD8+ cell were not affected by the treatment (P > 0.05). These effects of clonidine on the IgG concentrations and the proportions of B-cells and CD8+ cells were dose-related. The highest increase was found in the hens treated with 10.0 mg/L of clonidine. These results suggest that the sympathetic nervous system is directly involved in regulating the chicken immune system via regulation of alpha-2-adrenergic receptor activations.