Although dietary arginine is a factor in immune function and disease resistance, the full range of effects has yet to be described. In this study, the effects of dietary arginine on leukocyte population changes were examined in the peripheral blood and the respiratory tract of chickens inoculated with infectious bronchitis virus (IBV) strain M41. At 2 wk of age, female line P2a White Leghorn-type chickens were randomly assigned to one of three diets with different arginine levels: a marginally deficient diet (0.5%), an adequate diet (1.0%), and a diet containing a high level of arginine (3.0%). All birds were inoculated with IBV at 4 wk of age, and then the peripheral blood and the respiratory lavage were collected at 1 and 7 d postinfection (DPI). The growth rate of birds that received 0.5% arginine was significantly lower than that of birds receiving 1.0 or 3.0% arginine, whereas the growth of the latter groups did not differ. The percentage and absolute number of heterophil (H) and the H/lymphocyte (L) ratio in the peripheral blood at 1 DPI significantly increased as dietary arginine increased. In the respiratory lavage at 1 DPI, the percentage of H also increased with dietary arginine increase. At 7 DPI, the percentage of CD8+ cells from birds fed the deficient diet was lower than those from birds fed the adequate diet and the diet containing a high level of arginine, whereas the cell surface density of CD8 antigen did not vary among groups. These results show that dietary arginine influences the character of the chicken cellular response to IBV and the distribution of responding leukocyte subpopulations in a target tissue for the infection.

This review considers the role of avian macrophages as a source of immune effector and immunoregulatory metabolites. Although considerable attention has been given to the importance of leukocytic cytokines, particularly the monokines such as interleukin-1 (IL-1), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), and transforming growth factor-beta (TGF-beta), metabolites produced by macrophages appear to be of equal importance in determining the progression of immune responses. The three metabolite categories that have received the greatest attention are the reactive oxygen species (ROS), the reactive nitrogen intermediates (RNI), and the eicosanoids. Additionally, the xenobiotic metabolites produced via cytochrome P450 activity mediate some immune-environmental interactions. Each of these four metabolite categories is subject to different requirements for metabolite production, and each has distinct effector functions. An understanding of macrophage metabolite regulation could allow improvements in avian health management and production via the effective control of metabolite production. The present review considers prior and recent information on the production of the metabolites by avian macrophages. Additionally, the potential ramifications of metabolite production and regulation are discussed.