IMMUNOLOGY Humoral Immune Response ... - Semantic Scholar

IMMUNOLOGY Humoral Immune Response Impairment Following Excess Vitamin E Nutrition in the Chick and Turkey AHARON FRIEDMAN,*,1 IDO BARTOV,† and DAVID SKLAN* *Department of Animal Sciences, Faculty of Agriculture, Food and Environmental Quality Sciences, Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel and †Department of Poultry Science, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel ABSTRACT The effect of high dietary intakes of vitamin E on antibody production was investigated in chicks and turkeys. Chicks were fed four diets with 0, 10, 30, and 150 mg/kg added vitamin E and turkeys were fed three diets with 0, 50, and 150 mg/kg added vitamin E. Antibodies produced in response to naturally occurring Escherichia coli and to Newcastle disease virus and turkey pox vaccines were determined. In chicks, antibody production in response to E. coli and Newcastle disease was affected by vitamin E nutrition: significantly higher responses were measured in chicks that received 0 and 10 mg/kg added vitamin E, whereas in chicks receiving 30 and 150 mg/kg, antibody production was significantly lower. In turkeys, concentrations of

circulating antibodies to Newcastle disease virus and to turkey pox were also influenced by dietary vitamin E: antibody titers to Newcastle disease and turkey pox vaccines were highest in groups receiving 0 mg/kg added vitamin E, whereas titer in groups receiving 150 mg/kg were significantly lower. Responses of groups receiving 50 mg/kg added vitamin E were slightly lower than groups receiving 0 mg/kg, though not significantly so in most cases. These results indicate that humoral immune responses are directly effected by vitamin E, and that excessive vitamin E intake has a detrimental effect on antibody production in chickens and turkeys.

(Key words: vitamin E, immune response, antibody, chick, turkey) 1998 Poultry Science 77:956–962

crease risk of cancer and infection in animals and humans (Kumari and Chandra, 1993). We have previously investigated effects of vitamin A and polyunsaturated fatty acids (PUFA) over a wide range of dosages on immune responses of chickens and turkeys (Sklan et al., 1994, 1995; Friedman and Sklan, 1995, 1997). Indeed, our investigations show that immune responses may be increased by supplemented vitamin A and PUFA; however, exceeding optimal levels severely impaired immune responses. Similar observations were made with responses of murine and chicken T lymphocytes and macrophages to a wide range of retinol dosages in vitro (Friedman et al., 1993; Halevy et al., 1994), thereby indicating direct effects of retinol on cells of the immune system. However, the detrimental effects of vitamin A and PUFA overnutrition could have also been due to the sensitivity of these micronutrients to oxidation (Chew, 1996). Because our rations in those studies were formulated with recommended levels of vitamin E, we considered the possibility that vitamin E supplementation would increase immune responsiveness by reducing

INTRODUCTION High intensity poultry production requires fastgrowing strains, usually at high stocking densities. With this type of husbandry, flocks are highly susceptible to infectious agents, either as a result of reduced immune potential (van der Zijpp, 1983; Lamont and Dietert, 1990), or as a result of deteriorating environmental hygiene (Alexander, 1990; Jones and Wilding, 1990; Law and Payne, 1990). One of several approaches to increase immune responsiveness in high intensity production is to supplement rations with micronutrients (Chew, 1996). The validity of this approach has become a widely debated issue, particularly because it may lead to overnutrition (Kumari and Chandra, 1993). With some exceptions, excessive intake of most macro- and micronutrients can have adverse effects on the immune system, and there is increasing proof that—in addition to effects on immune function—excess intakes of some nutrients could in-

Received for publication April 30, 1997. Accepted for publication February 21, 1998. 1To whom correspondence should be addressed: fridman@agri. huji.ac.il

Abbreviation Key: NDV = Newcastle disease virus; PUFA = polyunsaturated fatty acids; TP = turkey pox.

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EXCESS VITAMIN E IMPAIRS ANTIBODY RESPONSE TABLE 2. Composition of turkey basal diets

TABLE 1. Composition of chick basal diets Starter1

Ingredients Corn Soybean meal (44.5% protein) DL-Methionine Constant ingredients2 Calculated analysis Metabolizable energy, kcal Crude protein Crude fat

Finisher1

610 342 1.7 46.3

(g/kg) 670.3 282 1.4 46.3

2,885 206.0 36.0

2,950 183.9 37.3

1From

1 to 28 d and from 28 to 42 d of age, respectively. phosphate, 20; ground limestone, 11; soybean oil, 10; sodium chloride, 2.5; vitamin mix, 2.5; trace mineral mix, 0.3. The vitamin mix supplied (in milligrams per kilogram): retinol acetate 2.52; cholecalciferol, 0.05; menadione sodium bisulfite, 2; riboflavin, 5.6; calcium pantothenate, 11.2; niacin, 29.6; cyanocobalamine, 0.008; folacin, 0.8; pyridoxine hydrochloride, 2.4; thiamine hydrochloride, 0.8; biotin, 0.1; choline chloride, 200; butylated hydroxytoluene, 125. The mineral mix supplied (in milligrams per kilogram): Mn, 80; Zn, 50; Fe, 20; Cu, 5; I, 1.2; Co, 0.2; Se, 0.1. These minerals were added as MnSO4·H2O, ZnO, FeSO4·H2O, CuSO4·5H2O, KI, COCl2·6H2O, and Na2SeO3, respectively. 2Dicalcium

oxidation, thereby overcoming the detrimental effects of excess vitamin A and PUFA. This approach is supported by numerous studies showing that vitamin E supplementation, in comparison to depletion, increased immune responses in all animals studied (Meydani, 1995; Finch and Turner, 1996), including chickens and turkeys (Tengerdy, 1990; Morandi et al., 1993; Ferket et al., 1995). Hence, the present study was undertaken to investigate effects of high intakes of vitamin E on the humoral immune response in chicks and turkeys.

Ingredients Wheat Sorghum Corn Soybean meal (44.5% protein) Fishmeal DL-Methionine Oil Constant ingredients1 Calculated analysis Metabolizable energy, Mcal Crude protein Crude fat

Starter1

Grower1

135 50 244 453 60 17 10 31

(g/kg) 178 50 244 413 60 7 18 31

2,750 280 35

2,800 640 39

1From

1 to 28, and from 28 to 70 d of age, respectively. phosphate, 14; ground limestone, 7; sodium chloride, 2; vitamin mix, 5; trace mineral mix, 3. The vitamin mix supplied (in milligrams per kilogram): retinol acetate, 3.5; cholecalciferol, 0.05; menadione sodium bisulfite, 2; riboflavin, 5; calcium pantothenate, 11; niacin, 20; cyanocobalamine, 0.01; folacin, 0.6; pyridoxine hydrochloride, 2; thiamine hydrochloride, 0.8; biotin, 0.1; choline chloride, 200; butylated hydroxytoluene, 125. The mineral mix supplied (in milligrams per kilogram): Mn, 80; Zn, 50; Fe, 25; Cu, 5; I, 1.2; Co, 0.2; Se, 0.1. These minerals were added as MnSO4·H2O, ZnO, FeSO4·7H2O, CuSOr·5H2O, KI, CoCl2·6H2O, and Na2SeO3, respectively. 2Dicalcium

heated battery brooders that were placed in a temperature-controlled room at 20 C until 6 wk of age. Fluorescent light was provided continuously in both rooms. Turkeys were raised in pens in a temperature and light controlled room at 30 C up to 1 wk of age at 27 C until 3 wk of age and at 20 C until 12 wk of age.

Determination of Vitamin E MATERIALS AND METHODS

Birds, Diets, and Experimental Design Day-old White Rock (Cobb) male chicks and British United Turkey poults were weighed, wing-banded, and divided into groups (n = 13), so that mean group weights and individual weight distribution were equal within the groups. Six groups of chicks and five groups of turkeys were assigned to each of the four and three diets, respectively, containing different levels of added vitamin E supplied as DL-a-tocopheryl acetate. Chick basal diets (Table 1) were supplemented with 0, 10, 30, and 150 mg/ kg and turkey basal diets (Table 2) were supplemented with 0, 50, and 150 mg/kg. The vitamin mix in the basal diets did not contain added vitamin E, and their analyzed ingredient-derived a-tocopherol content averaged 8 and 10 mg/kg for chick and turkey diets, respectively. The diets (in mash form) and water were provided for ad libitum intake. Chicks were weighed at weekly intervals and turkeys every 3 wk. Chicks were raised in electrically

2M.B.T.,

Jerusalem, Israel.

a-Tocopherol in feeds and serum was determined by reverse phase high performance liquid chromatography on a C18 column with fluorescence detection as previously described (Sklan et al., 1995).

Management and Vaccinations At 7 d of age, the number of chicks and turkeys was reduced to 10 per group by eliminating the two lightest and one heaviest birds. Vaccinations were performed according to standard vaccination programs implemented in local chick and turkey farms. Chicks were vaccinated against Newcastle disease virus (NDV)2 by im inoculation on d 10 of age (attenuated live virus), followed by a booster im injection administered on d 17 of age (heatkilled NDV)2. Turkeys were vaccinated against NDV and turkey pox (TP).2 Newcastle disease virus, as attenuated live virus, was given in drinking water at 8 d of age, and booster inoculations were administered im at 21 d of age (heat-killed NDV together with attenuated live TP virus) and at 49 d of age (heat-killed NDV alone). Blood samples from both chicks and turkeys were drawn from the jugular vein before and at weekly intervals after each immunization.

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FRIEDMAN ET AL.

Assay of Antibody Production Serum of individual birds was collected and stored at –70 C. Antibodies specific for NDV or Escherichia coli in chicks and NDV or TP in turkeys were detected in sera by means of an ELISA (Friedman and Sklan, 1989; Friedman, 1991; Sklan et al., 1994). In brief, dilutions of sera were added to microtiter plates previously coated with E. coli, NDV, or TP vaccine antigens3 (50 mg/mL) in carbonatebicarbonate buffer pH 9.6. After five washes to remove excess unbound antibody, plates were blocked with BSA diluent/blocking solution3 and either peroxidase conjugated goat anti-turkey IgG (H+L)3 or peroxidase conjugated goat anti-chicken IgG (H+L)3 were added, respectively, and then bound antibodies were detected by the addition of 3,3′5,5′-tetramethylbenzidine.3 Antibody binding is expressed as absorbance units at 405 nm, and results are group averages ± SEM. Serum without antibody activity against the tested antigens was prepared from unimmunized birds (Friedman and Sklan, 1989).

Statistical Analysis Differences between the experimental treatments were examined by analysis of variance using two-tailed t tests to test differences between treatments using the General Linear Models procedure of SAS.4 Significance was P < 0.05 unless otherwise stated.

Natural antibodies specific for E. coli appeared progressively with age and highest responses were observed in diets containing 0 and 10 mg/kg added vitamin E (Figure 1, 16 and 24 d of age). On Day 16, responses of groups receiving 0 and 10 mg/kg added vitamin E were significantly higher than those of groups receiving 30 and 150 mg/kg. By Day 24, responses of all groups increased, with that of the group receiving 10 mg/kg added vitamin E being significantly higher than those of groups receiving 0, 30, and 150 mg/kg. Similar results were observed at 34 d of age and with all serum dilutions tested (1:50, 1:200, 1: 400, 1:800, 1:3,200; data not shown). Essentially similar observations were made when antiNDV antibodies were determined (Figure 2, 16 and 24 d of age, serum dilution 1:800). Responses of chicks receiving 0 and 10 mg/kg added vitamin E were significantly higher than those of groups receiving 30 and 150 mg/kg at all ages (16, 24, and 34 d) and serum dilutions (1:50, 1:200, 1: 400, 1:800, 1:3,200) tested. Anti-NDV responses of groups receiving 30 and 150 mg/kg increased with age (Figure 2); however, this increase, although significant, was much lower than responses of groups receiving 0 and 10 mg/kg added vitamin E. Hence, antibody production in the chick, both natural and induced, is effected by vitamin E nutrition, with the highest responses occurring in chicks that received 0 and 10 mg/kg added vitamin E; whereas exceeding these dosages significantly reduced antibody production.

Excess Dietary Vitamin E and Humoral Immune Responses in Turkeys

RESULTS

Effects of Dietary Vitamin E on Growth, Feed Utilization, and Vitamin E Levels in Serum

The effects of added vitamin E on the antibody response to NDV virus in poults were progressive with age and inoculation (Figure 3). Thus, up to the first booster

Determination of vitamin E in the experimental diets confirmed the calculated values (data not shown). Added dietary vitamin E did not affect weight gain and feed efficiency in chicks (Table 3) or turkeys (Table 4). Table 5 shows serum concentrations of a-tocopherol in chicks (22 d of age) and turkeys (55 d of age). Circulating atocopherol levels increased with a-tocopherol intake; however, concentrations in turkeys were generally lower than those in chicks at similar dietary intakes.

Excess Vitamin E and Humoral Immune Responses in Chicks Two antibody populations were determined: antibodies specific for E. coli that appeared naturally with increasing age, and antibodies specific for antigens that were produced in response to a specific vaccine.

3Kirkegaard and Perry Laboratories, 4SAS Institute, Cary, NC 27513.

Gaithersburg, MD 20879.

FIGURE 1. Effects of added dietary vitamin E on production of natural anti-Escherichia coli antibodies in broiler chicks. Anti-E. coli antibodies (serum dilution 1:800) were determined by ELISA without prior immunization. Absorbance of naive serum was 0.01 to 0.05. Results are means of six replicates of 10 birds each ± SEM; significant differences between diets (P < 0.05) are indicated by lettering above SEM, bars not followed by the same letter differ significantly.

EXCESS VITAMIN E IMPAIRS ANTIBODY RESPONSE

FIGURE 2. Effects of added dietary vitamin E on production of antiNewcastle disease (NDV) antibodies in broiler chicks. Anti-NDV antibodies were determined by ELISA 1 wk after vaccination. Absorbance of naive serum was 0.01 to 0.05. Results are means of six replicates of 10 birds each ± SEM; significant differences between diets (P < 0.05) are indicated by lettering above SEM, bars not followed by the same letter differ significantly.

injection (Day 21) no differences were observed between the different treatments; this was observed in all serum dilutions tested (1:50, 1:200, 1:400, 1:800, 1:3,200; not shown). After boosting, response of all groups increased, with that of the group receiving 0 mg/kg added vitamin E being the highest, and the response of the group that received 150 mg/kg added vitamin E being the lowest, these differences, however, were not significantly differ-

FIGURE 3. Effects of added dietary vitamin E on production of antiNewcastle disease (NDV) antibodies in turkey poults. Anti-NDV antibodies (serum dilution 1:800) were determined by ELISA temporally after vaccination and booster inoculations. Absorbance of naive serum was 0.01 to 0.05. Results are means of five replicates of 10 birds each ± SEM; time points revealing significant differences between diets (P < 0.05) are indicated by asterisks and are detailed in results.

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FIGURE 4. Effects of added dietary vitamin E on production of antiturkey pox (TP) antibodies in turkey poults. Anti-TP antibodies were determined by ELISA 1 wk after vaccination. Absorbance of naive serum was 0.01 to 0.05. Results are means of five replicates of 10 birds each ± SEM; significant differences between diets (P < 0.05) are indicated by lettering above SEM, bars not followed by the same letter differ significantly.

ent. The anti-NDV immune response decayed with time; however, the response of the group receiving 0 mg/kg added vitamin E appeared to decay at a slower rate, resulting in significantly higher responses on Days 41 and 49 when compared to responses of groups receiving 50 and 150 mg/kg added vitamin E. A second booster injection was administered by 49 d of age. As a result, responses of all diet groups increased (Figure 3). The response of the group receiving 0 mg/kg added vitamin E developed a significantly higher response by Day 56, which persisted until Day 70, when the experiment was terminated. The response of the group receiving 50 mg/ kg added vitamin E peaked by Day 63 and persisted till Day 70; these responses were lower, but not significantly so, from those of the group receiving 0 mg/kg added vitamin E. The responses of the group that received 150 mg/kg added vitamin E peaked by Day 54 and then declined to preboost levels by Day 70; the peak response of this group was significantly lower than peak responses of other diet groups. Similar observations were made with all tested serum dilutions (not shown). The vaccination program also included immunization against TP by 21 d of age, and anti-TP antibodies were measured on Day 28 (Figure 4). Responses of groups receiving 0 and 50 mg/kg added vitamin E were significantly higher than that of the group receiving 150 mg/kg. Hence, in the turkey, dietary vitamin E level had progressive effects on maximal antibody production and its duration; optimal effects were observed in groups receiving no added vitamin E, whereas higher dosages impaired the intensity and duration of antibody production.

DISCUSSION We have shown here that intakes of vitamin E at levels exceeding NRC recommendations as much as

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FRIEDMAN ET AL. TABLE 3. Weight gain and gain to feed ratios of chicks fed different levels of vitamin E in diet1 1 to 28 d of age Added vitamin E

Weight change

(mg/kg) 0 10 30 150 SEM F-ratio P

(g) 1,063 1,045 1,063 1,055 15.4 0.298 NS

1Results

28 to 41 d of age

Gain:feed

Weight change

Gain:feed

(g:g) 0.604 0.604 0.609 0.600 0.005 0.656 NS

(g) 867 860 848 876 16.8 0.512 NS

(g:g) 0.465 0.467 0.465 0.469 0.003 0.432 NS

are means of six replicates of 10 birds each.

tocopherol is reviewed as a bioregulator, modulating both the lipoxygenase and the cyclooxygenase pathways at the level of arachidonate oxidation (Chan, 1993). Eicosanoids regulate immune responses at many different levels and tocopherol could, therefore, mediate direct effects on immunity (Brigham, 1989). These effects might be expressed in several immune-related functions, as different prostanoids are produced by different immune system cells (Brigham, 1989). Another possible explanation for these results is the finding that most of the so-called antioxidants, including carotenoids, tocopherol, and ascorbate, act as both antioxidants and prooxidants under conditions determined by their concentration, redox potential, and the chemistry of the cell (Jacob and Burri, 1996; Schwatz, 1996). Thornton et al. (1995) have described how a-tocopherol and gtocopherol change from antioxidants to prooxidants with increases in concentration in smooth muscle cell cultures challenged with arachidonic acid. A similar change in the behavior of a-tocopherol from anti- to prooxidant at high concentrations has been reported in aqueous model systems (Cillard and Cillard, 1980), in human low density lipoproteins (Bowry et al., 1995), and in hemorrhagic toxicity (Takahashi, 1995). Increasing concentrations of tissue tocopherol as produced by the high dietary intake in both chickens and turkey may well induce oxidative changes that are detrimental for

15-fold (NRC, 1994), impair antibody production in both chick and turkey, with no adverse effects on growth or feed utilization. In both avian species examined, optimal effects of vitamin E nutrition for antibody production were observed within similar dose ranges. The highest antibody production in the chick, natural or induced, occurred in chicks that received 0 or 10 mg added vitamin E/kg feed. In the turkey, the effects of vitamin E nutrition on antibody production became apparent after boosting; highest antibody titers and longest duration of the anamnestic immune response were obtained by a concentration of 10 mg vitamin E/kg feed (i.e., no added vitamin E). In both species, higher levels of vitamin E led to reduced antibody production. These observations are in marked contrast to numerous studies supplementing low levels of vitamin E intake in chickens (Tengerdy, 1990; Meydani et al., 1992; Morandi et al., 1993), and in the turkey (Landers et al., 1975; Ferket et al., 1995). These reports indicate that vitamin E supplementation in feed boosted immune responses but had no adverse effects on growth or production. Furthermore, excess vitamin E provided as an adjuvant also improved immune responses (Franchini et al., 1991, 1995). Several possible mechanisms may be involved in these contrasting findings. Vitamin E concentrations can profoundly influence the eicosanoid profile. As such,

TABLE 4. Weight gain and gain to feed ratios of turkeys fed different levels of vitamin E in diet1 1 to 21 d of age Added vitamin E

Body weight

(mg/kg) 0 50 150 SEM F-ratio P

(g) 947 979 967 16 1.45 NS

1Results

21 to 42 d of age

Gain:feed

Weight change

(g:g) 0.69 0.68 0.69 0.02 1.05 NS

(g) 1,051 1,063 1,049 31 0.81 NS

are means of five replicates of 10 birds each.

42 to 65 d of age

Gain:feed

Weight change

Gain:feed

(g:g) 0.64 0.63 0.64 0.02 1.31 NS

(g) 2,015 1,987 2,037 45 1.22 NS

(g:g) 0.48 0.47 0.48 0.03 1.21 NS

EXCESS VITAMIN E IMPAIRS ANTIBODY RESPONSE TABLE 5. Vitamin E concentrations in serum of chicks and turkeys Species Chickens

Turkeys

Vitamin E added

Serum vitamin E1

(mg/kg) 0 10 30 150 0 50 150

(mg/mL) 2.37 ± 1.18c 4.31 ± 1.08c 8.62 ± 1.17b 36.63 ± 1.07a 1.43 ± 0.61c 4.13 ± 0.86b 21.60 ± 2.81a

a–cValues for each species with no common superscript differ significantly (P < 0.05). 1Means ± SEM of 6 (chicks) and 5 (turkeys) replicates containing 10 birds per group.

antibody production, although at the same time improve the oxidative stability of meat (Sklan et al., 1983. Bartov and Frigg, 1992; Bartov et al., 1997). Thus, the effects of tocopherol supplementation at low dietary intakes will be to enhance protection against oxidation, enhancing antibody production, whereas as concentrations increase, prooxidation may occur, decreasing circulating antibody levels. These mechanisms indicate that immune responses are directly affected by vitamin E, and these detrimental effects differ from those induced by high dietary intakes of vitamin A and PUFA. Thus, overnutrition of vitamins A and E and PUFA are clearly involved in immune response suppression and because the effects of these nutrients appear to occur independently, it would be of interest to investigate their possible interactive effects on immune responses of poultry.

ACKNOWLEDGMENTS This study was supported in part by the Head Scientist of the Ministry of Agriculture, Tel-Aviv, Israel, the Poultry Marketing Board, Tel-Aviv, Israel, and BASF, Mannheim, Germany.

REFERENCES Alexander, D. J., 1990. Paramyxoviridae. Pages 121–136 in: Poultry Diseases. F.T.W. Jordan, ed. Bailliere Tindall, London, UK. Bartov, I., and M. Frigg, 1992. Effect of high concentration of dietary vitamin E during various age periods on performance, plasma vitamin E and meat stability of broiler chicks at 7 weeks of age. Br. Poult. Sci. 33:393–402. Bartov, I., D. Sklan, and A. Friedman, 1998. Effect of vitamin A on the oxidative stability of broiler meat during storage: lack of interaction with vitamin E. Br. Poult. Sci. 38: 255–257. Bowry, V. W., D. Mohr, J. Cleary, and R. Stocker, 1995. Prevention of tocopherol mediated peroxidation in ubiquinol-10-free human low density lipoprotein. J. Biol. Chem. 270:5756–5763. Brigham, K. L., 1989. Mediators of the inflammatory process: prostanoids. Pages 1–14 in: Mediators of the Inflammatory

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Process. P. M. Henson and R. C. Murphy, ed. Elsevier, Amsterdam, The Netherlands. Chan, A. C., 1993. Vitamin E and the arachidonic acid cascade. Pages 197–207 in: Vitamin E—Its Usefulness in Health and in Curing Diseases. M. Mino, ed. S. Karger, Basel, Switzerland. Chew, B. P., 1996. Importance of antioxidant vitamins in immunity and health in animals. N. American Nutrition Conferences III. Anim. Feed Sci. Technol. 59:1–3. Cillard, J., and P. Cillard, 1980. Prooxidant effect of alphatocopherol on essential fatty acids in aqueous media. Ann. Nutr. Aliment. 34:579–591. Ferket, P. R., M. A. Qureshi, J. D. Garlich, D. V. Rives, and M. T. Kidd, 1995. The effect of vitamin E on turkey performance. Misset World Poult. 11:13–15. Finch, J. M., and R. J. Turner, 1996. Effect of selenium and vitamin E on the immune responses of domestic animals. Res. Vet. Sci. 60:97–106. Franchini, A., S. Bertuzzi, C. Tosarelli, and G. Manfreda, 1995. Vitamin E in viral inactivated vaccines. Poultry Sci. 74: 666–671. Franchini, A., M. Canti, G. Manfreda, S. Bertuzzi, G. Asdrubali, and C. Franciosi, 1991. Vitamin E as adjuvant in emulsified vaccine for chicks. Poultry Sci. 70:1709–1715. Friedman, A., 1991. Induction of immune response to protein antigens by subcutaneous co-injection of water-miscible vitamin A derivatives. Vaccine 9:122–128. Friedman, A., O. Halevy, M. Schrift, Y. Arazi, and D. Sklan, 1993. Retinoic acid promotes proliferation and induces expression of retinoic acid receptor-alpha gene in murine T lymphocytes. Cell. Immunol. 152:240–248. Friedman, A., and D. Sklan, 1989. Antigen specific immune response impairment in the chick as influenced by vitamin A. J. Nutr. 119:790–795. Friedman, A., and D. Sklan, 1995. Effect of dietary fatty acids on antibody production and fatty acid composition of lymphoid organs in broiler chicks. Poultry Sci. 74: 1463–1469. Friedman, A., and D. Sklan, 1997. Effect of dietary fatty acids on humoral immune response in turkeys. Br. Poult. Sci. 38: 342–348. Halevy, O., Y. Arazi, D. Melamed, A. Friedman, and D. Sklan, 1994. Retinoic acid receptor-alpha gene expression is modulated by dietary vitamin A and by retinoic acid in chicken T lymphocytes. J. Nutr. 124:2139–2146. Jacob, R. A., and B. J. Burri, 1996. Oxidative damage and defense. Am. J. Clin. Nutr. 63:985S–990S. Jones, R. C., and G. P. Wilding, 1990. Rhinotracheitis of turkeys. Pages 121–136 in: Poultry Diseases. F.T.W. Jordan, ed. Bailliere Tindall, London, UK. Kumari, B. S., and R. K. Chandra, 1993. Overnutrition and immune responses. Nutr. Res. 13(Suppl. 1):S3–S18. Lamont, S. J., and R. R. Dietert, 1990. New directions in poultry genetics. Pages 497–541 in: Poultry Breeding and Genetics. R. D. Crawford, ed. Elsevier, Amsterdam, The Netherlands. Landers, M. H., G.R.J. Law, and E. W. Kienholz, 1975. The effect of dietary selenium and vitamin E on the immune response of turkeys. Poultry Sci. 54:1784–1788. Law, W. A., and L. N. Payne, 1990. The poultry industry. Pages 1–10 in: Poultry Diseases. F.T.W. Jordan, ed. Bailliere Tindall, London, UK. Meydani, S. N., 1995. Vitamin E. Lancet 345:170–175.

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FRIEDMAN ET AL.

Meydani, S. N., M. Hayek, and L. Colman, 1992. Influence of vitamins E and B6 on immune responses. Ann. N.Y. Acad. Sci. 669:125–140. Morandi, C., U. Cavinato, and G. Vanini, 1993. Immune response in poultry and vitamin E. Rivista Avicoltura 62: 29–31. National Research Council, 1994. Nutrient Requirements of Poultry. 9th rev. ed. National Academy Press, Washington, DC. Schwatz, J. L., 1996. The dual roles of nutrients as antioxidants and prooxidants: their effects on tumor cell growth. J. Nutr. 126:1221S–1227S. Sklan, D., D. Melamed, and A. Friedman, 1994. The effect of varying levels of vitamin A on immune response in the chick. Poultry Sci. 73:843–847. Sklan, D., D. Melamed, and A. Friedman, 1995. The effect of varying levels of vitamin A on immune response in the turkey. Br. Poult. Sci. 36:385–392.

Sklan, D., Z. Tenne, and P. Budowski, 1983. The effect of dietary fat and tocopherol on lipolysis and oxidation in turkey meat stored at different temperatures. Poultry Sci. 62:2017–2021. Takahashi, O., 1995. Haemorrhagic toxicity of a large dose of alpha-, beta-, gamma-, and delta-tocopherols, ubiquinone, beta-carotene, retinol acetate and L-ascorbic acid in the rat. Food Chem. Toxicol. 33:121–128. Tengerdy, R. P., 1990. The role of vitamin E in immune response and disease resistance. Ann. N. Y. Acad. Sci. 587: 24–33. Thornton, D. E., K. H. Jones, Z. Jiang, H. Zhang, G. Liu, and D. G. Cornwell, 1995. Antioxidant and cytotoxic tocopheryl quinones in normal and cancer cells. Free Radic. Biol. Med. 18:963–976. van der Zijpp, A. J., 1983. Breeding for immune responsiveness and disease resistance. World’s Poult. Sci. J. 39: 118–131.