In vivo effects of graded dietary levels of arginine on the body and lymphoid organs were investigated using Cornell K strain chickens of the B15/B15 haplotype. Two-week-old birds were fed an arginine-deficient basal diet (0.53% arginine) supplemented with additional arginine (up to 1.0% L-arginine to the diet). At four weeks of age, body weight, lymphoid organ weight, and concentrations of amino acids in plasma were measured. Arginine supplementation produced significant increases in plasma arginine (from 200 nM in chicks fed the basal diet to 2,000 nM in chicks receiving the 1.5% arginine diet) and ornithine concentrations (from 17 nM in chicks fed the basal diet to 500 nM in chicks receiving the 1.5% arginine diet). The arginine-deficient diet reduced body weight gain (P < 0.0001) and thymus, spleen, and bursa of Fabricius weights (P < 0.05). In contrast to the bursa weight, the thymus and spleen weights, as percentages of body weight, were also decreased (P < 0.05). This study suggests that arginine markedly influences lymphoid organ development, with a more pronounced effect on the thymus and spleen than on the bursa of Fabricius.

Diets specifically deficient in selenium (Se) and/or vitamin E or adequate in both nutrients were fed to chicks from the time of hatching. Lymphoid organs (bursa, thymus, and in some instances, spleen) were collected from chicks 7-35 days of age. Growth of the chicks fed these diets was monitored over the experimental period as was lymphoid organ growth. The development of the primary lymphoid organs was further assessed by histological techniques and the organ contents of vitamin E (a-tocopherol) and Se were determined. Specific deficiencies of either Se or vitamin E were found to significantly impair bursal growth as did a combined deficiency. Thymic growth was impaired only by the combined deficiency diet. Severe histopathological changes in the bursa resulted from the combined deficiency and these were detectable by 10-14 days after hatching. These changes were characterized by a gradual degeneration of the epithelium and an accompanying depletion of lymphocytes. Similar changes, although slower to develop and less severe, were observed in the thymus as a result of the combined deficiency. When both serum and tissue levels of vitamin E and Se were monitored, it was observed that these were rapidly and independently depleted by the specific deficiency diets. These data suggest that the primary lymphoid organs are major targets of Se and vitamin E dietary deficiencies and provide a possible mechanism by which immune function may be impaired.

We have examined the effects of repeated endotoxin administration in vivo and in vitro on the induction of nitric oxide synthase (NOS). In vivo, hepatic NOS activity and mRNA were increased markedly by the administration of Escherichia coli lipopolysaccharide (LPS). The change in hepatic NOS activity coincided with a marked accumulation of hepatic citrulline. Both enzyme activity and citrulline concentration returned to normal by 12 h after LPS administration. At this time, a subsequent administration of endotoxin caused no change in either NOS mRNA, NOS activity, or citrulline concentration, and thus an endotoxin-refractory state for nitric oxide (NO) synthesis was established. Normal sensitivity was reestablished by 24 h after the initial dose. In vitro studies using both a macrophage cell line (HD11) and primary macrophages indicated that LPS pretreatment caused cells in culture to become completely refractory to subsequent stimulation by LPS. Finally, we tested the hypothesis that NO may be involved in the development of the refractory state. Various inhibitors blocked the initial synthesis of NO by > 90% but failed to influence the development of the refractory state. Our study demonstrates both in vivo and in vitro that NO synthesis is completely blocked after repeated exposure to endotoxin by a mechanism that appears to be pretranslational. This model of early endotoxin tolerance may provide insight into the molecular mechanisms that regulate expression of the NOS gene.

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.

The avian inflammatory response to intraperitoneal (i.p.) Sephadex injection produces macrophages which display characteristics of an increasingly activated state over time. We examined elicited chicken peritoneal exudate cells (PECs) with respect to superoxide anion production, arachidonic acid metabolism and cell surface Ia and transferrin receptor (TfR) expression from 4 to 96 h after i.p. stimulation. Avian PECs showed the highest level of superoxide release when harvested just 4 h after injection, and did not produce PGE2 or 6-keto PGF1 alpha. Early (4-h) PECs produced elevated amounts of thromboxane as compared to later (42-h) macrophages. Expression of both Ia and TfR increased between 4 and 24 h after Sephadex stimulation; TfR remained elevated through 96 h, but Ia declined after 42 h. Some aspects of chicken macrophage regulation of superoxide anion, thromboxane release, and surface antigen expression are in contrast with those reported for mouse macrophages.