Selenium and immune cell functions. II. Effect on lymphocyte-mediated cytotoxicity

Selenium (Se) is an essential nutritional factor with a chemopreventive potential. This study examined the ability of C57BL/6J mice, maintained for 8 weeks on Se-deficient (0.02 ppm Se), normal (0.20 ppm Se), or Se-supplemented (2.00 ppm Se) Torula yeast-based diets, to generate cytotoxic lymphocytes (CTL) and to destroy tumor cells. CTL were generated in vivo by intraperitoneal immunization with P815 cells and in vitro by allogeneic stimulation of cells from animals maintained on a normal diet in media supplemented with 1 x 10(-9) to 1 x 10(-6) M Se (as selenite). Lymphocytes from animals maintained on the Se-supplemented diet had a greater ability to destroy tumor cells than lymphocytes from animals maintained on the normal diet, whereas Se deficiency reduced the cytotoxicity. The effects on cytotoxicity were accompanied by parallel changes in the levels of lymphotoxin produced. The greatest enhancement of tumor cytodestruction occurred with supplementation of 1 x 10(-7) M Se, whereas with 1 x 10(-6) M there was inhibition of the cytotoxic responses. The stimulatory effect of Se occurred during the phase of CTL generation rather than during the lytic phase of cytotoxicity. These results indicated that Se supplementation enhances CTL generation and the ability of a host to destroy malignant cells, whereas Se deficiency has the opposite effect.     

Effect of in vitro selenium supplementation on bovine sperm motility

The effects of selenium (Se) on motility of bovine spermatozoa were evaluated in two experiments. In Experiment 1, increasing doses of Se alone or with vitamin E were found to increase motility in Se concentrations up to 1 mug/ml. However, Se alone had a greater effect than did Se with vitamin E. The sperm motility response to Se concentrations from background to 1 mug/ml on motility best fit a quadratic equation with a maximum at about .65 mug Se/ml. In Experiment 2, the effect of Se addition before and after freezing was evaluated. This experiment demonstrated that treatment of semen with Se before freezing significantly increased the post-thaw motility as compared with portions of the same ejaculate which were not treated. Treatment after thawing produced motilities which were intermediate and not significantly different from either pre-freezing supplementation or no supplementation at all. These data indicate that some semen exhibits a greater percentage of motile sperm when Se is added prior to freezing, however, no information is yet available on the fertility of Se-treated semen.     

Effect of incubation temperature on motility and cAMP content of bovine sperm

We have used a change in temperature to vary sperm motility in order to see if changes in glucose consumption and cellular concentration of ATP, ADP, AMP, and cyclic AMP (cAMP) are correlated with the temperature-dependent control of motility. Effect of temperature on the kinetic parameters of adenylate cyclase and cyclic nucleotide phosphodiesterase also were studied. Glucose consumption rate was independent of adenine nucleotide concentration or energy charge. Furthermore, the percentage of progressively motile sperm and velocity of motile sperm were independent of mean cAMP concentration, in contrast to previously published data presented as evidence for the modulation of progressive motility of sperm via changes in cAMP concentration.     

Stabilization of adenylate energy charge and its relation to human sperm motility.

The adenylate energy charge of human ejaculated spermatozoa was studied when the sperm motility was perturbed by varying pH, prolonged incubation, and caffeine. Between pH 8 and 9, which was optimal for the sperm motility, the energy charge was in the physiological range of 0.8 to 0.9. Above pH 9, the mobility, ATP content, and adenine nucleotide pool declined rapidly but the energy charge was maintained slightly below 0.8. Below pH 8, the motility also dropped drastically, but the ATP, nucleotide pool, and energy charge fell only slightly. Prolonged incubations of the spermatozoa decreased the motility, ATP, and nucleotide pool. However, the energy charge would remain above 0.6. Caffeine stimulation of the motility caused a rapid fall of ATP and the reduction of the physiological energy charge by 0.2 unit, unless glucose was added. Imidazole which reduced the caffeine-stimulated motility did not alter the physiological energy charge of the spermatozoa. The study showed that the spermatozoa could maintain the energy charge above 0.6 under stress.     

The effects of organic selenium supplementation on the rumen ciliate population in sheep

The effect of selenium supplementation on the rumen protozoan population of sheep was demonstrated. Both the total and generic counts of rumen ciliates in sheep fed a diet with basal Se content (70 microg/kg dry matter) were compared to those of animals given feed supplemented with inorganic (disodium selenite) or organic Se (selenized yeast) (310 microg/kg dry matter). The genera of Entodinium, Isotricha, Dasytricha, Ophryoscolex, Diploplastron and Polyplastron occurred in all sheep except for the control, in which Ophryoscolex was not observed. The population of Ophryoscolex caudatus f. tricoronatus was significantly higher in sheep supplemented with organic Se than in animals given inorganic Se (by 160 %). Supplementation of feed with selenized yeast induced significant growth in the Diploplastron population (by 63 %) while no change occurred in sheep given selenite. The populations of Dasytricha ruminantium and Polyplastron multivesiculatum were higher than control in both Se-supplemented groups. The ciliate population of Entodinium spp. was not influenced by Se supplements. Our results suggest a protective effect of Se feed supplementation on the development of some rumen ciliate species in young ruminants.     

Stimulation of rhesus monkey sperm capacitation by cyclic nucleotide mediators

Capacitation of rhesus monkey spermatozoa was assessed by monitoring sperm flagellar beat and trajectory changes during incubation in vitro and by determining sperm penetration into rhesus oocytes and hamster zona-free ova. Rhesus sperm capacitation in vitro depended on the addition to the culture medium of the cyclic nucleotide mediators, caffeine and dibutyryl cyclic AMP. Capacitation was correlated with the development of hyperactivated motility. Spermatozoa treated with the cyclic nucleotide mediators, and showing hyperactivated motility, penetrated 57.4% of all rhesus oocytes and fertilized 88.9% of mature rhesus oocytes that were morphologically normal. Control spermatozoa did not penetrate any of the eggs. Some sperm penetration into hamster ova occurred but was not statistically significant. These data provide a basis for achieving in-vitro fertilization in the rhesus monkey and information on specific sperm motility characteristics associated with fertilizing ability.     

Selenium content and distribution in rat tissues irradiated with gamma rays

The effects of supplementation with selenous yeast and ionizing radiation on selenium (Se) content and distribution were evaluated in rat tissues (liver, kidney, spleen, heart, muscle, blood, front brain, hind brain, hypothalamus, pituitary, adrenal glands, testes, and hair). This study had 16 Se-supplemented (0.5 μg Se/d) and 16 placebo adult male Wistar rats. One half of the animals (eight Se-supplemented and eight placebos) were irradiated with a single dose of 4.2 Gy from a Co-60 source and sacrificed 7 d after irradiation along with nonirradiated animals and analyzed for Se content determination. The data obtained showed that selenous yeast supplementation increased Se levels in rat tissues (highest increases in hypothalamus, 161%; hind brain, 126%; spleen, 110%; and adrenal gland, 105%). Ionizing radiation induced significant changes in Se content and distribution (decrease in liver, blood, hair, femoral muscle, spleen, and hypothalamus; increase in kidney, testes, adrenal glands, and brain of placebo group). Supplementation with selenous yeast reduces changes in Se content and distribution after irradiation. It seems that the animal tissue susceptibility to oxidative damage may be correlated to their ability to retain Se in tissues.     

Selenium-vitamin E supplementation in infertile men

In order to verify the hypothesis that selenium (Se) and vitamin E (Vit E) could improve male fertility, nine oligoasthenoteratozoospermic men were supplemented for a period of 6 mo with Se and Vit E. Compared to the baseline period (presupplementation) of 4 mo, statistically significant increases were observed for Se and Vit E levels, sperm motility, percent live, and percent normal spermatozoa. These improvements are likely to be “supplementation-dependent,” since all of the parameters returned to baseline values during the posttreatment period. None of the couples reported a pregnancy during the study. The HPLC analysis conducted on the serum of one of the patients showed the existence of at least six different Se-containing peaks, whose Se content was affected by supplementation. The mechanism(s) involved in these improvements of semen parameters is presently under investigation.     

Modulation of hypercholesterolemia-induced alterations in apolipoprotein B and HMG-CoA reductase expression by selenium supplementation

Various studies demonstrated a significant association between the trace element selenium (Se), hypercholesterolemia and the risk of cardiovascular disorders. Present study was aimed to reveal the role of Se supplementation in modulation of hypercholesterolemia-induced changes in apolipoprotein B (apoB) and 3-hydroxy 3-methylglutaryl co-enzyme A (HMG-CoA) reductase expression during experimental hypercholesterolemia in Sprague-Dawley male rats. Animals were fed 0.2 and 1 ppm Se-supplemented control diet as well as 2% cholesterol-supplemented diet for 3 months. Apolipoprotein B levels were measured by ELISA and Western blot. HMG-CoA reductase mRNA expression was studied by RT-PCR. ApoB levels increased significantly on 2% cholesterol-supplemented diet feeding. On 1 ppm Se supplementation apoB levels decreased significantly. HMG-CoA reductase mRNA expression decreased significantly on cholesterol-supplemented diet feeding and on 1 ppm Se supplementation the mRNA expression further decreased. So the present results demonstrate that 1 ppm Se supplementation is responsible for down regulation of apoB and HMG-CoA reductase expression during hypercholesterolemia. These findings highlight the therapeutic potential of selenium supplementation in lipid metabolism.     

Thyroid function and plasma selenium in chronic uremic patients on hemodialysis treatment

It has been shown recently that Selenium (Se), an essential trace element for humans, is involved in the regulation of thyroid function, since the enzyme that catalyzes the liver conversion of the thyroid hormone T4 to the more active form T3 is a selenoenzyme. In chronic uremic patients, low blood Se levels as well as thyroid function abnormalities are often found. The present study was carried out to verify whether any correlation exists between Se levels and thyroid function, and to evaluate possible changes in hormonal pattern during Se supplementation in 10 chronic uremic patients on hemodialysis (HD) treatment. Se was supplemented orally as sodium selenite over six consecutive months. Basic plasma Se levels were significantly lower in patients than in normal controls. Right from the start of Se supplementation, plasma Se concentration promptly normalized and leveled off in the normal range throughout the study. Significant increase of FT3 and reduction of TSH levels were detected during Se supplementation. In Se-supplemented patients, a significant direct correlation was also found between reverse T3 (rT3) and TSH, and a significant inverse correlation was found between Se and TSH. Our results suggest that Se deficiency in chronic uremic patients represents a factor influencing the thyroid function and that the Se status should be determined in the evaluation of thyroid metabolism in these patients.     

Adenine nucleotide changes at initiation of bull sperm motility.

Testicular and cauda epididymal sperm were obtained via catheters previously implanted in the rete testis and proximal vas deferens of bulls and were used to examine the relationships among sperm motility, cyclic adenosine 3':5'-monophosphate (cAMP) level, adenine nucleotide levels, and rates of glucose and oxygen consumption. Testicular, cauda epididymal, and ejaculated sperm contain cAMP-stimulated protein kinase, adenylate cyclase, and nucleotide phosphodiesterase. Treatment of the nonmotile testicular sperm with phosphodiesterase inhibitors resulted in a doubling of cellular cAMP concentration and a 25% increase in their glucose consumption. No change in motility, ATP level, or rate of oxygen consumption was observed. Sperm in neat cauda epididymal semen had flagellating tails but no progressive motility. Dilution of these sperm into glucose-containing buffer resulted in an increase in intracellular cAMP concentration and a decrease in ATP level with concomitant increases in ADP and AMP levels. These biochemical changes occurred within 30 s after dilution and apparently preceded the initiation of progressive motility by most cells. Since sperm in neat cauda epididymal semen became progressively motile when diluted with neat cauda epididymal plasma as well as accessory sex gland fluid or buffer, composition of the fluid surrounding the sperm is not responsible for the initiation of progressive motility upon dilution nor does cauda epididymal plasma contain an inhibitory factor. Perhaps release from contact immobilization provides the stimulation for the initial acquisition of progressive motility by cauda epididymal sperm. We conclude that during epididymal passage sperm develop from a cell physically unresponsive to changes in cAMP concentration to a form which initiates progressive motility upon changes in cAMP concentration.     

Dibutyryl cyclic AMP decreases capacitation time in vitro in mouse spermatozoa

Epididymal mouse sperm suspensions were preincubated for various times in medium containing glucose and/or dibutyryl cyclic AMP and then assessed for fertilizing ability in vitro, loss of the acrosome and motility changes. Capacitation time was significantly reduced by exposure to glucose and 0.1 mM-dbcAMP for 30 min as evidenced by early and synchronous fertilization of eggs, compared with glucose alone. Although this was accompanied by a precocious development of whiplash motility, the rate of acrosome loss in isolated sperm suspensions was not accelerated by the presence of exogenous cyclic nucleotide. Exposure of spermatozoa to 1 mM-dbcAMP in the presence of glucose resulted in very poor fertilization, but the effect could be prevented by withholding glucose until eggs were introduced; this may be due to free butyrate in the system since the inclusion of 1 mM-butyrate in glucose-containing medium had a similar inhibitory effect. Although cyclic nucleotide supported the acrosome reaction but not motility changes, no fertilization was obtained unless zonae were removed, when a low level of fertilization (30%) was observed. Both whiplash motility and acrosome loss are thus obligatory for sperm penetration of the zona and glycolytic metabolism supports both changes, perhaps by promoting endogenous generation of cyclic AMP to act as an intermediary in these two distinct phenomena.     

Effect of different levels and sources of zinc supplementation on quantitative and qualitative semen attributes and serum testosterone level in crossbred cattle (Bos indicus x Bos taurus) bulls

An experiment was conducted on 16 crossbred bulls (about 2 years of age, 316.2+/-0.77 kg average body weight), divided into groups I, II, III and IV to study the effect of different levels of Zn supplementation from inorganic and organic sources on semen quality. The animals in the first 3 groups were supplemented with 0, 35 and 70 ppm Zn from Zn sulfate, respectively and the animals in-group IV were supplemented with 35 ppm Zn as Zn propionate. Semen collection and evaluation was done in the first month (to assess semen quality at the start of the experiment) and 7th, 8th and 9th month of experimental feeding to evaluate the effect of supplemental Zn on semen attributes. We gave 6 months for Zn feeding, so that 3 sperm cycles of spermatogenesis had passed and the collected semen reflected the complete effect of Zn supplementation. Six ejaculates from each bull were collected and evaluated for semen quantitative (ejaculate volume, sperm concentration and sperm number per ejaculate) and qualitative characteristics (semen pH, mass motility, individual motility, sperm livability percent and abnormal sperm percent, percent intact acrosome, bovine cervical mucus penetration test, hypo-osmotic sperm swelling test) and activity of seminal plasma enzymes i.e., alkaline phosphatase, acid phosphatase, GOT and GPT. Testosterone level in the blood serum of crossbred bulls was also estimated. Mean values of semen quantitative and qualitative characteristics at the start of the experiment were statistically non significant (P > 0.05) in all the crossbred cattle bulls, however, there were statistically significant differences among the bulls of different groups after 6 months of zinc supplementation. Mean ejaculate volume (mL) was 2.37, 4.70, 5.86 and 6.38, respectively in groups I to IV, indicating a statistically significant (P < 0.05) higher semen volume in Zn-supplemented groups as compared to the control group of bulls. Similarly, sperm concentration (million.mL(-1)), live sperm (%) and motility (%) were significantly (P < 0.01) higher in Zn-supplemented groups as compared to the control group. The results of BCMPT and HOSST revealed a significant improvement in sperm functional ability in all the groups supplemented with Zn as compared to the control group. The activity of alkaline and acid phosphatase in seminal plasma was significantly (P < 0.05) higher in the Zn-supplemented groups, whereas GOT and GPT activities in seminal plasma were significantly (P < 0.05) lower in the Zn propionate supplemented group as compared to the control group. Testosterone concentration (ng.mL(-1)) in blood serum was significantly higher in animals of groups III and IV, as compared to control group. It may be concluded that Zn supplementation either in the inorganic or organic form in the diet of crossbred bulls improved the qualitative and quantitative attributes of semen; however, the number of sperm per ejaculate, mass motility and semen fertility test like bovine cervical mucus penetration was significantly higher in bulls given Zn in an organic form (Zn propionate) as compared to an inorganic form (Zn sulfate).     

Selenium-mediated differential response of β-glucosidase and β-galactosidase of germinatingTrigonella foenum-graecum

β-Glucosidase and β-galactosidase activity profile tested in different seeds during 24 h germination revealed reasonably high levels of activity inVigna radiata, Cicer arietinum, andTrigonella foenum-graecum. In all seeds tested, β-galactosidase activity was, in general, higher than that of β-glucosidase.T. foenum-graecum seedlings exhibited maximal total and specific activities for both the enzymes during 72 h germination. Se supplementation as Na₂SeO₃ up to 0.75 ppm was found to be beneficial to growth and revealed selective enhancement of β-galactosidase activity by 40% at 0.5 ppm Se. The activities of both the enzymes drastically decreased at 1.0 ppm level of Se supplementation. On the contrary, addition of Na₂SeO₃ in vitro up to 1 ppm to the enzyme extracts did not influence these activities. Hydrolytic rates of β-glucosidase in both control and Se-supplemented groups were enhanced by 20% with 0.05M glycerol in the medium and 30% at 0.1M glycerol. The rates were marginally higher in Se-supplemented seedlings than the controls, irrespective of added glycerol in the medium. In contrast, hydrolysis by β-galactosidase showed a trend of decrease in Se-supplemented seedlings compared to the control, when glycerol was present in the medium. Addition of Se in vitro in the assay medium showed no difference in the hydrolytic rate by β-galactosidase when compared to control, while the activity of β-glucosidase declined by 50%. Se-grown seedlings showed an enhancement of transglucosidation rate by 40% in the presence of 0.1M glycerol. The study reveals a differential response to Se among the β-galactosidase and β-glucosidase ofT. foenumgraecum with increase in the levels of β-galactosidase activity.     

Involvement of mitochondrial activity in mediating ELF‐EMF stimulatory effect on human sperm motility

It has recently been reported that the exposure of human spermatozoa to an extremely low frequency (ELF) electromagnetic field (EMF) with a square waveform of 5 mT amplitude and frequency of 50 Hz improves sperm motility. The functional relationship between the energy metabolism and the enhancement of human sperm motility induced by ELF‐EMF was investigated. Sperm exposure to ELF‐EMF resulted in a progressive and significant increase of mitochondrial membrane potential and levels of ATP, ADP and NAD⁺ that was associated with a progressive and significant increase in the sperm kinematic parameters. No significant effects were detected on other parameters such as ATP/ADP ratio and energy charge. When carbamoyl cyanide m‐chlorophenylhydrazone (CICCP) was applied to inhibit the oxidative phosphorylation in the mitochondria, the values of energy parameters and motility in the sperm incubated in the presence of glucose and exposed to ELF‐EMF did not change, thus indicating that the glycolysis was not involved in mediating ELF‐EMF stimulatory effect on motility. By contrast, when pyruvate and lactate were provided instead of glucose, the energy status and motility increased significantly in ELF‐EMF‐treated sperm. Under these culture conditions, the inhibition of glycolitic metabolism by 2‐deoxy‐D ‐glucose (DOG) again resulted in increased values of energy and kinematic parameters, indicating that gluconeogenesis was not involved in producing glucose for use in glycolysis. We concluded that the key role in mediating the stimulatory effects exerted by ELF‐EMF on human sperm motility is played by mitochondrial oxidative phosphorylation rather than glycolysis. Bioelectromagnetics 32:15–27, 2011. © 2010 Wiley‐Liss, Inc.     

Selenium-mediated biochemical changes in Japanese quails

The effect of selenium (Se) on collagen characteristics and glutathione peroxidase (GSH-Px) activity in the skin of Japanese quailsCoturnix coturnix japonica fed a formulated, semipurified, low-Se diet (basal) (0.05 ppm) was investigated. The quails exhibited severe Se-deficiency symptoms and significant reduction in skin GSH-Px activity at the end of 30 d. Selenium supplementation at a 2-ppm level restored the normal skin conditions and enhanced skin GSH-Px activity significantly. But a dietary Se level of 0.1 ppm was found to be inadequate in restoring the general skin conditions and GSH-Px activity. A markedly low total collagen content of about 23% was observed in the skin of quails fed the basal diet, compared to 39% of total collagen content in the skin of the 2-ppm Se-supplemented group. Molecular organization of skin collagen of quails on the basal and 0.1-ppm Se diet showed an abundance of monomeric forms with less crosslinks, compared to the presence of polymeric forms with more crosslinks, indicating enhanced stability in the skin collagen of quails on the 2-ppm diet. The delay in the in vitro fibril formation of collagen from the basal and 0.1-ppm Se groups, compared to a relatively faster rate in the case of the 2-ppm Se group, indicates a disturbance in the aggregation phenomenon of collagen. The increase in skin GSH-Px activity and concurrent increase in polymeric collagen on increasing the dietary Se level suggest a possible role for Se in collagen metabolism.     

Dietary selenium deficiency and supplementation differentially modulate the expression of two ER-resident selenoproteins (selenoprotein K and selenoprotein M) in the ovaries of aged mice: Preliminary data

In the present report, we determined the impact of dietary selenium (Se) deficiency and supplementation on the expression of two ER-resident selenoproteins i.e., Selenok and Selenom in the ovaries of aging mice. The mRNA expression of Selenok and Selenom (RT-qPCR) was significantly higher in the ovaries of mice fed diets supplemented with inorganic (ISe-S: 0.33 mg Se/kg) and organic (OSe-S: 0.33 mg Se/kg) Se compared to those fed a Se-deficient (Se-D: 0.08 mg Se/kg) diet and both Se-adequate (ISe-A: 0.15 mg Se/kg and OSe-A: 0.15 mg Se/kg) diets. Similarly, the protein signals of SELENOK (immunofluorescence assay) were also significantly higher in the Se-supplemented groups compared to those fed Se-D and Se-adequate (ISe-A and OSe-A) diets. Meanwhile, the rate of in vitro-produced blastocysts developing from MII oocytes was also evaluated and it was revealed that this rate was significantly higher in the Se-supplemented mice compared to those fed a Se-D diet. Altogether, the dietary Se supplementation increased the expression of Selenok (also its protein expression) and Selenom in the ovaries of aging mice, potentially contributing to an improved developmental potential of in vitro-matured M II oocytes.     

Selenium Supplementation Decreases Hepatic Fibrosis in Mice After Chronic Carbon Tetrachloride Administration

Oxidative stress stimulates fibrogenesis, and selenium (Se) has antioxidant properties. This study determined whether Se supplementation affects CCl₄-induced liver injury and fibrosis. Mice were administered CCl₄ over 4 weeks, while controls received olive oil. Se was provided as sodium selenite in the drinking water. Se increased liver Se-dependent glutathione peroxidase activity and decreased liver malondialdehyde after CCl₄. Se decreased liver inflammation but not necrosis caused by CCl₄. Se increased hepatocyte apoptosis after CCl₄ and the pro-apoptotic BAX and Bcl Xs/l proteins. Stellate cell apoptosis occurred only after CCl₄ in Se-supplemented mice. Se decreased stellate cell number and fibrosis after CCl₄. Liver matrix metalloproteinase-9 increased after CCl₄ with Se supplementation. In conclusion, Se supplementation decreased hepatic fibrosis after CCl₄ in the setting of decreased inflammation but increased apoptosis. The principal mechanisms for the decreased fibrosis are a lower number of collagen-producing stellate cells and increased collagen degradation.     

Effects of selenium supplementation on virus-induced inflammatory heart disease

The effects of 10 wk of selenium (Se) supplementation (5 ppm) in drinking water on immune responses and resistance to a myocarditic Coxsackie virus B3 (CB3) infection were studied in female Balb/c mice. Se supplementation reduced CB3-induced mortality: at day 14 postinoculation, survival was 58% in the Se-treated group as compared to 25% in the untreated group. Whole-blood glutathione peroxidase (GSH-Px) activity was elevated by 68% (p < 0.001) and Se content in the liver by 24% (p < 0.001). Red (RBC) and white blood cell (WBC) counts, as well as the number of cells in the spleen and thymus, were unaffected. The cellular counts of T-lymphocytes (CD4⁺, CD8⁺) and natural killer (NK⁺) cells in the blood were not affected. However, the CD4⁺/CD8⁺ ratio (5.2) tended to increase after Se supplementation (5.9). The spleen lymphoproliferative response to T and B-cell mitogens were increased by 9 and 43%, respectively (ns), in the Se-supplemented group. The total NK cell activity in blood and spleen showed minor increases, but when the activity in the blood was expressed per cell, the increase amounted to 35% (ns) with Se supplementation. The inflammatory and necrotic lesions in the ventricular myocardium at 7 and 14 d postinoculation were not significantly reduced by Se treatment, probably owing to the increased survival with Se even of mice with the most pronounced heart damage; comparable untreated mice were estimated to have died at day 14. Results indicate that modest doses of Se can improve immune function, which may increase the general resistance to this viral infection.