Murine neonates typically mount Th2-biased immune responses. This entails a cell-intrinsic component whose molecular basis is unknown. We found that neonatal CD4+ T cells are uniquely poised for rapid Th2 function. Within 24 h of activation, neonatal CD4+ cells made high levels of IL-4 and IL-13 mRNA and protein. The rapid high-level IL-4 production arose from a small subpopulation of cells, did not require cell cycle entry, and was unaffected by pharmacologic DNA demethylation. CpG methylation analyses in resting neonatal cells revealed pre-existing hypomethylation at a key Th2 cytokine regulatory region, termed conserved noncoding sequence 1 (CNS-1). Robust Th2 function and increased CNS-1 demethylation was a stable property that persisted in neonatal Th2 effectors. The transcription factor STAT6 was not required for CNS-1 demethylation and this state was already established in neonatal CD4 single-positive thymocytes. CNS-1 demethylation levels were much greater in IL-4-expressing CD4 single-positive thymocytes compared with unactivated cells. Together, these results indicate that neonatal CD4+ T cells possess distinct qualities that could predispose them toward rapid, effector-like Th2 function.
regulatory element binding protein and dietary lipid regulation of fatty acid synthesis in the mammary epithelium.
Effects of increased dietary energy and protein on the composition and functional capacities of blood mononuclear leukocyte populations from milk replacer-fed calves were investigated. Holstein bull calves (average age: 4.2 d; n = 19) were assigned randomly to one of two treatment groups. Treatment 1 calves (n = 9) were fed a 20% crude protein, 20% fat milk replacer at a rate of 1.4% body weight of dry matter/d for 8 wk, whereas treatment 2 calves (n = 10) were fed a 30% crude protein, 20% fat milk replacer at a rate of 2.5% body weight of dry matter per day. Composition and functional capacities of mononuclear leukocyte populations from blood samples collected at 4, 18, 32, 46, and 60 d of age were characterized by flow cytometry and ex vivo cell function assays. From 11 to 60 d of age, the mean daily weight gain of treatment 2 calves (1.20 kg/d) was greater than daily weight gain of treatment 1 calves (0.55 kg/d). At 60 d of age, the mean body weight of treatment two calves was 53% (39 kg) greater than the mean body weight of treatment 1 calves. Total numbers of blood leukocytes and the composition of the mononuclear leukocyte population were unaffected by the plane of nutrition. Mitogen-induced DNA-synthesis and immunoglobulin M secretion also were unaffected by dietary treatment. Blood mononuclear leukocytes from calves on intensified diets, however, produced less interferon-gamma and more inducible nitric oxide, suggesting that increased dietary energy and protein affects specific aspects of leukocyte function associated with cell-mediated immunity. The impact of altered interferon-gamma and NO production on the calf s susceptibility to infectious disease are not known. Mononuclear leukocyte populations from all calves also demonstrated age-related changes in composition and functional capacity, likely reflecting natural exposure to infectious agents and maturation of the calfs immune system.
Our previous work has shown that feeding 5 million international units (IU) of vitamin D3 to beef steers can produce tender strip loin and top round steaks. Our current experiment was designed to determine whether feeding two metabolites of vitamin D3, 25-hydroxyvitamin D3, and 1,25-dihysroxyvitamin D3, produces tender strip loin, top round, and top blade steaks more effectively than does supplemental vitamin D3 without leaving a substantial amount of residual vitamin D3 in muscle. Thirty-three continental crossbred steers were randomly allotted to one of four treatment groups. The first group was fed a placebo. The second group received 5 million IU of vitamin D3 each day for nine days and was slaughtered two days later. The third group received one dose of 125 mg of 25-hydroxyvitamin D3 four days before harvest, and the fourth group received one dose of 500 mg of 1,25-dihydroxyvitamin D3 three days before harvest. Blood samples were collected before treatment and at the time of slaughter for subsequent analysis of calcium, vitamin D3, 25-hydroxyvitamin D3, and 1,25-dihydroxyvitamin D3 concentrations in plasma. Steaks from the longissimus lumborum (strip loin) and semimembranous (top round) muscles were collected from each animal and aged for 8, 14, and 21 days, and steaks from the infraspinatus were collected and aged for 14 and 21 days. All steaks were analyzed for tenderness by Warner-Bratzler shear force determination. Concentrations of vitamin D3 in plasma were higher in vitamin D3-treated cattle (P < 0.0001). Concentrations of plasma 25-hydroxyvitamin D3 were increased in 25-hydroxyvitamin D3-treated cattle, but not as high as vitamin D3-treated cattle (P < 0.0001). 1,25-Dihydroxyvitamin D3 concentrations were higher in 1,25-dihydroxyvitamin D3-treated animals compared with all treatments (P < 0.0001). Supplementing steers with vitamin D3 increased the concentration of vitamin D3 and 25-hydroxyvitamin D3 in the meat of all muscles sampled (P < 0.0001). Supplementing steers with 25-hydroxyvitamin D3 increased the concentration of 25-hydroxyvitamin D3 in meat, but to an amount less than half that of cattle treated with vitamin D3. Warner-Bratzler shear force analysis showed that feeding 1,25-dihydroxyvitamin D3 did not significantly lower shear force values, but supplemental vitamin D3 and 25-hydroxyvitamin D3 produced longissimus lumborum and semimembranous steaks with lower shear force values (P < 0.06). Analysis of Western blots showed that longissimus lumborum and semimembranous steaks from cattle fed supplemental vitamin D3 and 25-hydroxyvitamin D3 (but not steaks from cattle fed 1,25-dihydroxyvitamin D3), had greater proteolysis of troponin T to a 30 kDa component.
The physiological response of the preruminant calf to sustained exposure to moderate cold has not been studied extensively. Effects of cold on growth performance and health of preruminant calves as well as functional measures of energy metabolism, fat-soluble vitamin, and immune responsiveness were evaluated in the present study. Calves, 3 to 10 d of age, were assigned randomly to cold (n = 14) or warm (n = 15) indoor environments. Temperatures in the cold environment averaged 4.7 degrees C during the study. Frequent wetting of the environment and the calves was used to augment effects of the cold environment. Temperatures in the warm environment averaged 15.5 degrees C during the study. There was no attempt to increase the humidity in the warm environment. Preventative medications or vaccinations that might influence disease resistance were not administered. Nonmedicated milk replacer (20% crude protein and 20% fat fed at 0.45 kg/d) and a nonmedicated starter grain fed ad libitum were fed to all calves. Relative humidity was, on average, almost 10% higher in the cold environment. Warm-environment calves were moderately healthier (i.e., lower respiratory scores) and required less antibiotics. Scour scores, days scouring, and electrolyte costs, however, were unaffected by environmental temperature. Growth rates were comparable in warm and cold environments, although cold-environment calves consumed more starter grain and had lower blood glucose and higher blood nonesterified fatty acid concentrations. The nonesterified fatty acid and glucose values for cold-stressed calves, however, did not differ sufficiently from normal values to categorize these calves as being in a state of negative-energy balance. Levels of fat-soluble vitamin, antibody, tumor necrosis factor-alpha, and haptoglobin were unaffected by sustained exposure to moderate cold. These results support the contention that successful adaptation of the dairy calf to cold is dependent upon the availability of adequate nutrition.
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