The immunobiology of zinc

Zinc-binding proteins (metallothionein and alpha-2 macroglobulin) and immunosenescence

Zinc is a relevant trace element for the efficiency of the entire immune system. The binding of zinc with some proteins, such as metallothioneins (MT) and alpha-2 macroglobulin (alpha-2M) is crucial for the immune efficiency during ageing and in age-related diseases, because these proteins may be involved in antagonistic pleiotropic effects. Indeed, the presence of chronic inflammation during ageing, generally, induces overexpression of these proteins that, due to their original biological function in fighting stressor agents, continuously sequester intracellular zinc. As a consequence, a low zinc ion availability may appear in aged organisms leading to impairments of the immune response at thymic and extrathymic levels with the risk of the appearance of age-related diseases. Therefore, MT and alpha-2M turn from protective in "young-adult age" to harmful agents in "ageing" following the basic assumption of an evolutionary theory of ageing, named the "antagonistic pleiotropy", which suggests that a trade off between early beneficial effects and late negative outcomes can occur at a genetic and molecular level. On the other hand, some polymorphisms of MT (MT2A) and alpha-2M have been associated with atherosclerosis or Alzheimer disease, respectively. Physiological zinc supplementation in elderly restores the thymic endocrine activity and innate immune response (NK cell cytotoxicity) and increases the survival rate in old mice. Therefore, zinc supplementation is useful to achieve health longevity because these zinc-binding proteins may regain their original protective task against oxidative damage with, thus, a beneficial impact on immune response.

Effect of improved zinc status on T helper cell activation and TH1/TH2 ratio in healthy elderly individuals

Mild zinc deficiency is a common condition in healthy elderly individuals leading to impaired cell-mediated immune response. Here we report the effect of improved zinc status on TH1/TH2 balance and on the activation status of T helper cells in 19 healthy elderly subjects aged 69.8 +/- 5.1 years. Our investigations revealed a mild zinc deficiency which was adjusted by oral zinc supplementation for seven weeks. Improved serum zinc levels significantly reduced levels of activated T helper cells whereas changes in TH1/TH2 ratio (determined by CCR4 and CCR5 expression) were not observed. These findings suggest that elderly individuals may benefit from moderate zinc supplementation due to improved immune response leading to reduced incidences of autoimmune diseases and infections.

Uptake of dietary micronutrients from artificial diets by larval Heliothis virescens

Micronutrient assimilation from artificial diet by larvae of Heliothis virescens during selenium (Se) supplementation was studied. The metal content of pupae and plugs of the artificial diet on which they had developed from hatching was analyzed by inductively coupled plasma-mass spectrometry. Levels of the metals Cr, Co, Fe, Mg, Mn, Ni, Se, Na, and Zn were not bioaccumulated from the diet regardless of the amount of Se added to the diet. Only pupal Cu and Mo bioaccumulation were found to be altered significantly by dietary Se supplementation. Larvae fed Zn, which was found in higher levels in pupae than diet, had a deleterious response to increasing levels of dietary Zn. Larvae fed Cr, found in higher levels in diet than in pupae, were not adversely affected when increasing levels of Cr were added to the diet. Based on this analysis, metals were identified that might well impact the fitness of a given colony of insects in relation to their diet.

Flow cytometric measurement of labile zinc in peripheral blood mononuclear cells

Labile (i.e., free or loosely bound) zinc has the potential to modulate cellular function. Therefore, a flow cytometric assay for the measurement of labile zinc was developed to facilitate the investigation of the physiological roles of zinc. The zinc-sensitive fluorescent probe FluoZin-3 was used to quantify the amount of labile zinc in peripheral blood mononuclear cells isolated from human blood. Maximal fluorescence and autofluorescence of the probe were measured after the addition of zinc in the presence of the ionophore pyrithione, or the membrane-permeant chelator N,N,N',N'-tetrakis-(2-pyridyl-methyl)ethylenediamine, respectively. In this way, the intracellular concentrations of labile zinc in resting cells were estimated to be 0.17 nM in monocytes and 0.35 nM in lymphocytes. The method was successfully employed to monitor phorbol 12-myristate 13-acetate-induced zinc release, which occurred in monocytes but not lymphocytes, and the displacement of protein-bound zinc by the mercury-containing compounds HgCl(2) and thimerosal. Costaining with dyes that emit at higher wavelengths than FluoZin-3 allows multiparameter measurements. Two combinations with other dyes are shown: loading with propidium iodide to measure cellular viability and labeling with antibodies against the surface antigen CD4. This method allows measurement of the concentration of biologically active labile zinc in distinct cell populations.

Cytotoxic effect of zinc-citrate compound on choriocarcinoma cell lines

This study investigated the cytotoxic effect of zinc-citrate compound (CIZAR) on choriocarcinoma cell lines. Primary cultured normal trophoblast cells (NPT), human tumorigenic poorly differentiated trophoblast cell line (HT), and choriocarcinoma cell line (BeWo) were exposed to different concentrations of CIZAR and cultured at different times. Cell viability was determined by CCK-8 assay. The effects on cell cycle progression, population distribution and apoptotic incidence were determined by flow cytometry. The appearance of apoptosis was confirmed by DNA laddering and DAPI staining. The quantitative analysis of telomerase was measured by TRAPeze telomerase detection kit. The molecular mechanism of CIZAR-induced apoptosis was examined with Western blot analysis and colorimetric caspase-3 activity assay. In in vitro condition, CIZAR had a selective cytotoxic effect on choriocarcinoma cell line in dose- and time-dependent patterns. Flow cytometric analysis, DNA laddering, and DAPI staining indicated that BeWo cells only have been induced apoptosis by CIZAR. Shortening of telomere was also observed only in BeWo cells. Results also displayed that CIZAR-induced apoptosis involves the up-regulation of p21(WAF1) and Bax protein and down-regulation of Bcl-2 which were accompanied by the activation of caspase-3. Taken together, our results suggest that CIZAR is an apoptotic inducer in malignant trophoblast cells (BeWo).

Zinc requirements and the risks and benefits of zinc supplementation

The adult human contains 2-3g of zinc, about 0.1% of which are replenished daily. On this basis and based on estimates of bioavailability of zinc, dietary recommendations are made for apparently healthy individuals. Absent chemical, functional, and/or physical signs of zinc deficiency are assumed indicative of adequacy. More specific data are seldom available. Changing food preferences and availability, and new food preparation, preservation, and processing technologies may require re-evaluation of past data. Conservative estimates suggest that 25% of the world's population is at risk of zinc deficiency. Most of the affected are poor, and rarely consume foods rich in highly bioavailable zinc, while subsisting on foods that are rich in inhibitors of zinc absorption and/or contain relatively small amounts of bioavailable zinc. In contrast, among the relatively affluent, food choice is a major factor affecting risk of zinc deficiency. An additional problem, especially among the relatively affluent, is risk of chronic zinc toxicity caused by excessive consumption of zinc supplements. High intakes of zinc relative to copper can cause copper deficiency. A major challenge that has not been resolved for maximum health benefit is the proximity of the recommended dietary allowance (RDA) and the reference dose (RfD) for safe intake of zinc. Present recommendations do not consider the numerous dietary factors that influence the bioavailability of zinc and copper, and the likelihood of toxicity from zinc supplements. Thus the current assumed range between safe and unsafe intakes of zinc is relatively narrow. At present, assessment of zinc nutriture is complex, involving a number of chemical and functional measurements that have limitations in sensitivity and specificity. This approach needs to be enhanced so that zinc deficiency or excess can be detected early. An increasing number of associations between diseases and zinc status and apparently normal states of health, where additional zinc might be efficacious to prevent certain conditions, point at the pharmacology of zinc compounds as a promising area. For example, relationships between zinc and diabetes mellitus are an area where research might prove fruitful. In our opinion, a multidisciplinary approach will most likely result in success in this fertile area for translational research.

Zinc as an ambivalent but potent modulator of murine hair growth in vivo- preliminary observations

Oral zinc (Zn(2+)) is often employed for treating hair loss, even in the absence of zinc deficiency, although its mechanisms of action and efficacy are still obscure. In the current study, we explored the in vivo effects of oral zinc using the C57BL/6 mouse model for hair research. Specifically, we investigated whether continuous administration of high-dose ZnSO(4) x 7H(2)O (20 mg/ml) in drinking water affects hair follicle (HF) cycling, whether it retards or inhibits chemotherapy-induced alopecia (CIA) and whether it modulates the subsequent hair re-growth pattern. Here, we show that high doses of oral zinc significantly inhibit hair growth by retardation of anagen development. However, oral zinc also significantly retards and prolongs spontaneous, apoptosis-driven HF regression (catagen). Oral zinc can also retard, but not prevent, the onset of CIA in mice. Interestingly, Zn(2+) treatment of cyclophosphamide-damaged HFs also significantly accelerates the re-growth of normally pigmented hair shafts, which reflects a promotion of HF recovery. However, if given for a more extended time period, zinc actually retards hair re-growth. Thus, high-dose oral zinc is a powerful, yet ambivalent hair growth modulator in mice, whose ultimate effects on the HF greatly depend on the timing and duration of zinc administration. The current study also encourages one to explore whether oral zinc can mitigate chemotherapy-induced hair loss in humans and/or can stimulate hair re-growth.

Zinc: a multipurpose trace element

Zinc (Zn) is one of the most important trace elements in the body and it is essential as a catalytic, structural and regulatory ion. It is involved in homeostasis, in immune responses, in oxidative stress, in apoptosis and in ageing. Zinc-binding proteins (metallothioneins, MTs), are protective in situations of stress and in situations of exposure to toxic metals, infections and low Zn nutrition. Metallothioneins play a key role in Zn-related cell homeostasis due to their high affinity for Zn, which is in turn relevant against oxidative stress and immune responses, including natural killer (NK) cell activity and ageing, since NK activity and Zn ion bioavailability decrease in ageing. Physiological supplementation of Zn in ageing and in age-related degenerative diseases corrects immune defects, reduces infection relapse and prevents ageing. Zinc is not stored in the body and excess intakes result in reduced absorption and increased excretion. Nevertheless, there are cases of acute and chronic Zn poisoning.

Apoptosis of blood mononuclear cells in alcoholic liver cirrhosis. The influence of in vitro ethanol treatment and zinc supplementation

Ethanol consumption induces apoptosis in a variety of tissues, among others in liver and lymphoid tissue. Zinc has been shown to influence apoptosis of blood mononuclear cells by inhibiting the mitochondrial pathway of cell death. The aim of this study was to examine the influence of zinc on spontaneous and in vitro alcohol-induced apoptosis of peripheral blood mononuclear cells (PBMCs) of patients with alcoholic cirrhosis. PBMCs were isolated from the blood of 26 patients with cirrhosis and 20 healthy controls. PBMCs and among them CD4+ T helper cells of cirrhotic patients exhibited accelerated spontaneous (without treatment) apoptosis in vitro. When apoptosis was induced in vitro by treating cells with 80 mM ethanol, CD8+ T lymphocytes of a healthy control were more sensitive to ethanol treatment than those of cirrhotic patients. Thirty micromolar zinc supplementation inhibited both spontaneous and ethanol-induced apoptosis of immune cells derived from the blood of the healthy control and cirrhotic patients. In sera of patients with cirrhosis, an elevated level of IL-12, but also sFas (CD95) and sFas ligand (sFasL) was detected. Moreover, in vitro, PBMCs of cirrhotic patients spontaneously released more sFas and sFasL than control PBMCs. Ethanol treatment significantly increased sFas, but decreased sFasL release from PBMCs of cirrhotic patients, while it only slightly affected control cells. As zinc supplementation did not significantly influence sFas or sFasL release, it seems likely that it is rather the mitochondrial pathway of ethanol-related immune cell death that may be inhibited by zinc supplementation.

Zinc and Cadmium Interactions in a Renal Cell Line Derived from Rabbit Proximal Tubule

BACKGROUND

The aim of this work was to characterize the relationship between zinc (Zn(2+)) and cadmium (Cd(2+)) and the toxic effects of Cd(2+) in immortalized renal proximal tubule cells RP1.

METHODS

An RP1 cell line was developed from primary cultures of microdissected S1 and S2. Uptakes of (65)Zn and (109)Cd and competitive experiments with Cd(2+) and Zn(2+) were performed and kinetic parameters were determined. Oxygen consumption, metallothionein synthesis, and necrotic and apoptotic phenomena were studied.

RESULTS

Kinetic parameters indicate that (65)Zn (Km = 71.8 +/- 10.6 microM) and (109)Cd (Km = 23.3 +/- 2.0 microM) were both transported by a saturable carrier-mediated process. Competition between Cd(2+) and Zn(2+) uptake was reciprocal. Cd(2+) induced an increase in necrosis and apoptosis, and a decrease in oxygen consumption, depending on Cd(2+) concentrations. Concomitant addition of Zn(2+) (10 microM) reduced the number of necrotic and apoptotic cells and maintained oxygen consumption at control levels. Cd(2+) alone, or in the presence of Zn(2+), increased metallothionein levels, whereas Zn(2+) alone did not.

CONCLUSION

Zn(2+) and Cd(2+) probably share the same transporter in the proximal tubule. Cd(2+) caused necrotic and apoptotic cell death. Cd(2+) toxicity may occur through an effect on the mitochondrial electron transport chain and not on metallothionein synthesis. Zn(2+) protects against the renal cell toxicity of Cd(2+).

Zinc in pharmacological doses suppresses allogeneic reaction without affecting the antigenic response

Zinc is an essential trace element for the immune system. Previously it was shown that zinc inhibits alloreactivity. In our present in vitro experiments, it is shown that zinc maintains the antigenic potency of the host while blocking the allogeneic response. These results were observed in experiments using tetanus toxoid as a well-established recall antigen and the mixed lymphocyte culture as an in vitro model for allogeneic reaction. To prove the in vivo relevance, an ex vivo experimental setup was established. This involved participants taking zinc orally for 1 week. Here it is shown that in vivo zinc application induced the same effect of blocking the mixed lymphocyte culture without influencing tetanus toxoid stimulation. So far, no clinical application studies have been performed, but the observed selective suppression of allogeneic reaction by zinc is the first step towards a new generation of immunosuppressants.

Oxidative stress in viral hepatitis and AIDS

Dominant types of viral hepatitis are presently A, B, and C with prophylactic immunization available only for A and B. Hepatitis B and C and human immunodeficiency virus (HIV) infection constitute a worldwide scourge and treatment is far from satisfactory. Each produces severe oxidative stress (OS) and secondary cellular damage of varying severity and, as in toxic hepatitis, progression and regression are dependent on redox balance between oxidation and antioxidation. Experimental and clinical studies suggest that xenobiotics and co-infections exert cumulative, detrimental effects on their pathogeneses and further deplete antioxidants. It is proposed therefore that in the clinical management of these infections and especially in their early stages, considerable benefit should accrue from antioxidant repletion at dosages substantially above recommended daily allowances (RDAs) in conjunction with a nutritious high protein diet. Because plasma zinc and selenium concentrations are very low, their replenishment by high dosages is urgent and mandatory particularly in advanced HIV infections bordering on acrodermatitis enteropathica. Also recommended is their long-term continuance at high normal levels.

Effect of zinc supplementation on immune and inflammatory responses in pediatric patients with shigellosis

BACKGROUND

Several studies showed benefits of long-term zinc supplementation on the incidence, severity, and duration of diarrhea and on the incidence of respiratory infections. Prolonged zinc supplementation also improves cell-mediated immunity in severely malnourished children.

OBJECTIVE

We studied the effect of short-term zinc supplementation on intrinsic and specific immune and inflammatory responses in moderately malnourished children with acute shigellosis.

DESIGN

A randomized, double-blind, placebo-controlled trial was conducted in Shigella-infected children aged 12-59 mo. Elemental zinc (20 mg) and a multivitamin containing vitamins A and D, thiamine, riboflavin, nicotinamide, and calcium at twice the recommended dietary allowance were given daily for 2 wk to the zinc group (n = 28), whereas the multivitamin alone was given to the control group (n = 28). Standard antibiotic therapy was given to all patients.

RESULTS

Serum zinc concentrations increased in both groups during convalescence; however, zinc supplementation showed a significant effect. The lymphocyte proliferation response in the zinc group increased relative to that in the control group (P = 0.002), but no significant effects were seen on concentrations of cytokines (interleukin 2 and interferon gamma) released from mitogen-stimulated mononuclear cells or on concentrations of cytokines (interleukin 2, interferon gamma, and interleukin 1beta) in feces. Among the antigen [lipopolysaccharide and invasion plasmid-encoded antigen (Ipa)]-specific antibodies, plasma Ipa-specific immunoglobulin G responses at day 30 were significantly higher in the zinc group than in the control group. However, the 2 groups did not differ significantly in the other antigen-specific responses in plasma and stool.

CONCLUSION

A 14-d course of zinc supplementation during acute shigellosis increases the lymphocyte proliferation response and the Ipa-specific immunoglobulin G response.

The immune response to pneumococcal polysaccharide vaccine in zinc-depleted mice

Zinc depletion affects several facets of the immune system and the resistance to infections. We assessed the effect of zinc deprivation on the immune response to the pneumococcal polysaccharide antigens in the commercially available Pneumovax pneumococcal vaccine. Young female BALB/c mice were fed diets with 2.7, 5.8 or 25 micro g of elemental zinc per mg diet. After six weeks of pair feeding, there were significant differences in the mean body weights between the feeding groups and we demonstrated a dose response of the zinc level in the diet on growth. The induced zinc deficiency had no discernible effect on the antipneumococcal polysaccharide immunoglobulin M (IgM) response following immunization with the pneumococcal vaccine. Although zinc depletion has a detrimental effect on the immune system, the murine T-cell-independent response to antigens such as those in the pneumococcal polysaccharide capsule does not seem to be affected.

Intestinal and systemic immune responses to an oral cholera toxoid B subunit whole-cell vaccine administered during zinc supplementation

Zinc plays a critical role in the normal functioning of the immune system. We investigated whether zinc sulfate administered orally to adult zinc-replete volunteers modulates systemic and intestinal immune responses to an oral killed cholera toxoid B subunit (CTB) whole-cell cholera vaccine. The 30 participants were immunized twice, with a 17-day interval. The vaccinees in the intervention group ingested 45 mg of elemental zinc thrice daily for 9 days starting 2 days before each vaccine dose. The median serum anti-CTB immunoglobulin A (IgA) and IgG responses from day 0 to day 30, i.e. after two vaccine doses, were 13-fold lower (P value for identical distribution, <0.005) in the zinc-supplemented compared to the nonsupplemented vaccinees. The median serum vibriocidal responses from baseline to after one (day 0 to day 17) and two (day 0 to day 30) vaccine doses were at least sixfold (P = 0.033) and fourfold (P = 0.091) higher, while the median fecal anti-CTB IgA response after two doses was estimated to be fourfold higher (P = 0.084) in the zinc-supplemented vaccinees. These observations show that zinc reduces the antitoxin and may enhance the antibacterial responses in serum. Zinc may also improve the intestinal antitoxin immune response. Oral zinc administration has the potential to modify critical immune responses to antigens applied to mucosal surfaces.

A global view of the selectivity of zinc deprivation and excess on genes expressed in human THP-1 mononuclear cells

Among the micronutrients required by humans, zinc has particularly divergent modes of action. cDNA microarray and quantitative PCR technologies were used to investigate the zinc responsiveness of known genes that influence zinc homeostasis and to identify, through global screening, genes that may relate to phenotypic outcomes of altered dietary zinc intake. Human monocytic/macrophage THP-1 cells were either acutely zinc depleted, using a cell-permeable zinc-specific chelator, or were supplemented with zinc to alter intracellular zinc concentrations. Initially, genes associated with zinc homeostasis were evaluated by quantitative PCR to establish ranges for fold changes in transcript abundance that might be expected with global screening. Zinc transporter-1 and zinc transporter-7 expression increased when cellular zinc increased, whereas Zip-2 expression, the most zinc-responsive gene examined, was markedly increased by zinc depletion. Microarrays composed of approximately 22,000 elements were used to identify those genes responsive to either zinc depletion, zinc supplementation, or both conditions. Hierarchal clustering and ANOVA revealed that approximately 5% or 1,045 genes were zinc responsive. Further sorting based on this pattern of the zinc responsiveness of these genes into seven groups revealed that 104 genes were linearly zinc responsive in a positive mode (i.e., increased expression as cellular zinc increases) and 86 genes that were linearly zinc responsive in a negative mode (i.e., decreased expression as cellular zinc increases). Expression of some genes was responsive to only zinc depletion or supplementation. Categorization by function revealed numerous genes needed for host defense were among those identified as zinc responsive, including cytokine receptors and genes associated with amplification of the Th1 immune response.

The immune system: a target for functional foods?

The immune system acts to protect the host from infectious agents that exist in the environment (bacteria, viruses, fungi, parasites) and from other noxious insults. The immune system is constantly active, acting to discriminate 'non-self' from 'self'. The immune system has two functional divisions: the innate and the acquired. Both components involve various blood-borne factors (complement, antibodies, cytokines) and cells. A number of methodologies exist to assess aspects of immune function; many of these rely upon studying cells in culture ex vivo. There are large inter-individual variations in many immune functions even among the healthy. Genetics, age, gender, smoking habits, habitual levels of exercise, alcohol consumption, diet, stage in the female menstrual cycle, stress, history of infections and vaccinations, and early life experiences are likely to be important contributors to the observed variation. While it is clear that individuals with immune responses significantly below 'normal' are more susceptible to infectious agents and exhibit increased infectious morbidity and mortality, it is not clear how the variation in immune function among healthy individuals relates to variation in susceptibility to infection. Nutrient status is an important factor contributing to immune competence: undernutrition impairs the immune system, suppressing immune functions that are fundamental to host protection. Undernutrition leading to impairment of immune function can be due to insufficient intake of energy and macronutrients and/or due to deficiencies in specific micronutrients. Often these occur in combination. Nutrients that have been demonstrated (in either animal or human studies) to be required for the immune system to function efficiently include essential amino acids, the essential fatty acid linoleic acid, vitamin A, folic acid, vitamin B6, vitamin B12, vitamin C, vitamin E, Zn, Cu, Fe and Se. Practically all forms of immunity may be affected by deficiencies in one or more of these nutrients. Animal and human studies have demonstrated that adding the deficient nutrient back to the diet can restore immune function and resistance to infection. Among the nutrients studied most in this regard are vitamin E and Zn. Increasing intakes of some nutrients above habitual and recommended levels can enhance some aspects of immune function. However, excess amounts of some nutrients also impair immune function. There is increasing evidence that probiotic bacteria improve host immune function. The effect of enhancing immune function on host resistance to infection in healthy individuals is not clear.

Reactive oxygen species modulate Zn(2+)-induced apoptosis in cancer cells

Some recent evidence has suggested a protective role of zinc against cancer. The mechanism by which zinc exerts this action has not been defined and, in particular, it has not been clarified whether zinc may directly act on cancer cells and the molecular mechanisms involved in this effect. In this study, we examined the in vitro effect of zinc on the apoptosis of mouse TS/A mammary adenocarcinoma cells, studying the zinc-dependent modulation of the intracellular levels of reactive oxygen species (ROS) and of p53 and Fas/Fas ligand pathways. We showed that zinc concentrations ranging from 33.7 to 75 muM Zn(2+) induced apoptosis in mammary cancer cells. The apoptosis was associated with an increased production of intracellular ROS, and of p53 and Fas/Fas ligand mRNA and protein. Zn(2+) induced a faint metallothionein response in TS/A cells in comparison with mouse lymphocytes. The treatment of tumor cells with the antioxidant N-acetylcysteine was able to prevent Zn(2+)-induced apoptosis, as well as the increase of p53 and Fas ligand protein induced by zinc. The data demonstrate that zinc exerts a direct action on mammary cancer cells inducing ROS-mediated apoptosis and that the effect may be mediated by the ROS-dependent induction of p53 and Fas/Fas ligand.

Pneumococcal pulmonary infection, septicaemia and survival in young zinc-depleted mice

The aim of the present study was to explore whether mice fed a diet low in Zn (2.0 mg Zn/kg diet) for a relatively short period of time were more prone to severe Streptococcus pneumoniae infection than mice fed a normal diet (25 mg elemental Zn/kg). The Zn-deficient mice were compared with mice in two Zn-adequate control groups; one pair-fed and another with free access to the diet. After 2 weeks feeding, the mice were infected intranasally under anaesthesia with a suspension containing about 10(7) pneumococci. Clinical status was observed every day and blood samples were examined for S. pneumoniae every second day for a week. All infected mice examined carried the infecting strain intranasally. The survival time and time before positive blood culture were significantly shorter in the Zn-depleted group than in the pair-fed Zn-adequate group (hazard ratios 15.6 and 3.2, and respectively). At the end of the observation period, ten of the twelve mice in the Zn-deficient group were dead while one of twelve and two of twelve were dead in the two Zn-adequate control groups. This study shows that even acutely-induced Zn deficiency dramatically increases the risk of serious pneumococcal infection in mice.

Zinc-mediated regulation of caspases activity: dose-dependent inhibition or activation of caspase-3 in the human Burkitt lymphoma B cells (Ramos)

Divalent cations, including Zinc and Manganese ions, are important modulators of cell activation. We investigated the ability of these two divalent cations to modulate apoptosis in human Burkitt lymphoma B cells line (Ramos). We found that Zinc (from 10 to 50 microM) inhibited Manganese-induced caspase-3 activation and apoptosis of Ramos cells. Higher concentration of Zinc (50 to 100 microM) did not prevent Manganese-mediated apoptosis but rather increased cell death among Ramos cells. This Zinc-mediated cell death was associated with apoptotic features such as cell shrinkage, the presence of phosphatidylserine residues on the outer leaflet of the cells, chromatin condensation, DNA fragmentation and decrease of mitochondrial transmembrane potential. Zinc-mediated apoptosis was associated with caspase-9 and caspase-3 activation as revealed by the appearance of active p35 fragment of caspase-9 and p19 and p17 of caspase-3 as well as in vivo cleavage of PARP and of a cell-permeable fluorogenic caspase-3 substrate (Phiphilux-G(1)D(2)). Both Zinc-mediated apoptosis and caspase-3 activation were prevented by the cell-permeable, broad-spectrum inhibitor of caspases (zVAD-fmk) or overexpression of bcl-2. In addition, we show that Zinc-induced loss of transmembrane mitochondrial potential is a caspase-independent event, since it is not modified by the presence of zVAD-fmk, which is inhibited by overexpression of bcl-2. These results indicate that depending on its concentration, Zinc can exert opposite effects on caspase-3 activation and apoptosis in human B lymphoma cells: concentrations below 50 microM inhibit caspase-3 activation and apoptosis whereas higher concentrations of Zinc activate a death pathway associated with apoptotic-like features and caspase-3 activation.

Zinc intervention on macrophages and lymphocytes response

Normal zinc levels are essential for the development and maintenance of immune functions; Zn deficiency is detrimental to the embryo and offspring of experimental animals, especially concerning immune development. It is known that Zn supplementation improves immune responses. To further explore the relation between Zn administration and the metal in vitro effects, we studied zinc (500 mg/l) supplementation impact on lymphocytes and macrophages and zinc in vitro effects, in BALB/c mice supplemented from gestation to lactation. Results show a significant increase in proliferation (assessed by 3H incorporation) in lymphocytes exposed to Zn (0.1 mM) in vitro, in 3-wk-old mice; this effect is annulled when the supplementation period is lengthened, indicating saturation of the mechanisms involved in zinc induced stimulation. Macrophages functional capacity assessed by erythrophagocytosis was also improved by Zn supplementation and furthermore by the in vitro exposure to the metal, in mice 3 wk old, this was also depressed by Zn accumulation due to the supplementation period extension (9 weeks). Results show an improvement in the immune parameters analysed due to zinc supplementation and to zinc in vitro exposure. Results also suggest the accumulation of zinc as a result of prolonged supplementation periods, suppresses the cells response to zinc in vitro.

Zinc, infections and immunosenescence

Infections may cause mortality in old age due to damaged immune responses. As zinc is required as a catalyst, structural (zinc fingers) and regulatory ion, it is involved in many biological functions, including immune responses. Low zinc ion bioavailability and impaired cell-mediated immunity are common in ageing and may be restored by physiological supplementation with zinc for 1-2 months, impacting upon morbidity and survival. This article reviews the role of zinc in immune efficacy during ageing, and also describes the main biochemical pathways involved in the role of zinc in resistance to infections in ageing in order to better understand the possible causes of immunosenescence.

Immune stimulating activity of two new chitosan containing adjuvant formulations

Recombinant proteins have potential as both human and veterinary vaccine antigens, but they are often weakly immunogenic and immunization with recombinant proteins may not elicit a significant immune response that recognizes the native protein. This report describes the immune stimulating activity of two new adjuvant formulations, a zinc-chitosan particle formulation designed to bind to histidine tagged recombinant proteins; and an emulsion formulation containing chitosan. BALB/c mice vaccinated with formulations comprising recombinant beta-human chorionic gonadotropin (betahCG) and each adjuvant had prolonged high titer antibodies that recognized both the recombinant betahCG and native hCG. betahCG is an established target for immunocontraceptive vaccines and a potential target for tumor immunotherapy. Isotype analysis of these antibodies revealed an IgG1 response in mice immunized with zinc-chitosan particles and a mixed IgG1, IgG2a and IgG2b response with the emulsion. These chitosan based adjuvant formulations were effective in sensitizing mice and guinea pigs for antigen specific DTH responses, indicating that these adjuvants stimulate both B and T lymphocytes. The ability of these adjuvants to stimulate significant responses with a poorly immunogenic recombinant protein suggests that they may have potential in developing vaccines based on synthetic peptides and subunit antigens.

Zinc and the immune system

Zn is an essential trace element for all organisms. In human subjects body growth and development is strictly dependent on Zn. The nervous, reproductive and immune systems are particularly influenced by Zn deficiency, as well as by increased levels of Zn. The relationship between Zn and the immune system is complex, since there are four different types of influence associated with Zn. (1) The dietary intake and the resorption of Zn depends on the composition of the diet and also on age and disease status. (2) Zn is a cofactor in more than 300 enzymes influencing various organ functions having a secondary effect on the immune system. (3) Direct effects of Zn on the production, maturation and function of leucocytes. (4) Zn influences the function of immunostimulants used in the experimental systems. Here we summarize all four types of influence on the immune function. Nutritional aspects of Zn, the physiology of Zn, the influence of Zn on enzymes and cellular functions, direct effects of Zn on leucocytes at the cellular and molecular level, Zn-altered function of immunostimulants and the therapeutic use of Zn will be discussed in detail.

Micronutrients and innate immunity

Micronutrients such as zinc, selenium, iron, copper, beta-carotene, vitamins A, C, and E, and folic acid can influence several components of innate immunity. Select micronutrients play an important role in alteration of oxidant-mediated tissue injury, and phagocytic cells produce reactive oxidants as part of the defense against infectious agents. Thus, adequate micronutrients are required to prevent damage of cells participating in innate immunity. Deficiencies in zinc and vitamins A and D may reduce natural killer cell function, whereas supplemental zinc or vitamin C may enhance their activity. The specific effects of micronutrients on neutrophil functions are not clear. Select micronutrients may play a role in innate immunity associated with some disease processes. Future studies should focus on issues such as age-related micronutrient status and innate immunity, alterations of micronutrients in disease states and their effect on innate immunity, and the mechanisms by which micronutrients alter innate immunity.

Therapeutic application of zinc in human immunodeficiency virus against opportunistic infections

The relevance of zinc in resistance to infections by virus, fungi and bacteria is recognized because of its pivotal role in the efficiency of the entire immune system, in particular in conferring biological activity to a thymic hormone called thymulin, which has differentiation properties on T-cell lines. In infection with human immunodeficiency virus (HIV), the zinc-bound form of thymulin (active thymulin, ZnFTS) is strongly reduced in stage IV of the disease (Centers for Disease Control and Prevention classification) with concomitant decrements in CD4(+) cell count and zincemia values. The zinc-unbound form of thymulin (inactive thymulin, FTS) is, in contrast, very high. The in vitro addition of zinc to plasma samples induces a recovery of the thymulin active form, suggesting low zinc bioavailability as the cause of impaired thymic functions with consequent CD4(+) depletion. An analysis of risk factors for the incidence of recidivism opportunistic infections shows CD4(+) depletion and zinc deficiency to have significant scores. Supplementation with zinc for 1 mo (45 mg Zn(2+)/d) associated with zidovudine (AZT) therapy in stage IV induces recovery of active zinc-bound thymulin, of zincemia, of CD4(+) cells with concomitant reduction (50%) of recidivism opportunistic infections compared with the AZT-treated group. Complete disappearance of recidivism by Candida aesophagea or Pneumocystis carinii is observed after supplementation with zinc. The relative risk factors (CD4(+) depletion and zinc-deficiency) have lower scores in the HIV-positive zinc-treated group, confirming, as such, the relevance of zinc in opportunistic infections that involve extracellular matrix. Such an assumption is indirectly confirmed with new HAART, where no opportunistic infections occur. Indeed, HIV RNA is inversely correlated with both CD4(+) and zincemia values (r = -0.73, P<0.01) in HAART-treated subjects. Lower scores for the same relative factors for the appearance of opportunistic infections are present in HAART-treated subjects compared with those treated with AZT. These findings, on the one hand, show the poor efficacy of AZT therapy compared with HAART therapy for the progression of HIV, but on the other hand, they suggest that the lack of occurrence of opportunistic infections by HAART may also result from major zinc bioavailability. This further supports the key role played by zinc against opportunistic infections in HIV with a possible independent effect by either HIV or the pathogens involved.

Zinc-altered immune function and cytokine production

Although the intriguing role of zinc as an essential trace element for immune function is well established, particular progress in determining the molecular principles of action of this ion was made recently. Leukocyte responsiveness is delicately regulated by zinc concentration. Zinc deficiency as well as supraphysiologic levels impair immune function. Furthermore, the activities of many immunostimulants frequently used in immunologic studies are influenced by zinc concentration. Therefore, our knowledge from in vitro studies is widely dependent on the zinc concentration, and when not in physiologic range, immunologic responses are artificially low. Decreased production of TH1 cytokines and interferon-alpha by leukocytes in the healthy elderly person is correlated with low zinc serum level. The defect in interferon-alpha production is reconstituted by the addition of physiologic amounts of zinc in vitro. Interestingly, zinc induces cytokine production by isolated leukocytes. Zinc induces monocytes to produce interleukin-1, interleukin-6 and tumor necrosis factor-alpha in peripheral blood mononuclear cells and separated monocytes. This effect is higher in serum-free medium. However, only in the presence of serum does zinc also induce T cells to produce lymphokines. This effect on T cells is mediated by cytokines produced by monocytes. Stimulation also requires cell-to-cell contact of monocytes and T cells. Information is presented to illustrate the concepts that the zinc concentration must be taken into account whenever in vitro studies are made or complex alterations of immune functions are observed in vivo.

The inhibitory effect of zinc on cadmium-induced cell apoptosis and reactive oxygen species (ROS) production in cell cultures

The prevention of apoptosis by Zn(2+) is a well-known phenomenon. Both in in vitro and in vivo Zn(2+) supplementation prevents apoptosis induced by a variety of agents, among them by cadmium ions. The target for protective action of Zn ions on cell apoptosis is still unknown. In this paper we have evaluated the effect of in vitro ZnCl(2) supplementation at a concentration corresponding to the physiological level (10 microM) and higher (50 microM), on apoptosis induced with different Cd concentrations in two cell types: HeLa human tumor cell line and bovine aorta endothelial cells (BAECs). We demonstrated that Zn supplementation, especially at 10 microM concentration, significantly inhibited apoptosis in both types of cells. To assess the mechanism involved in the Zn effect we examined the influence of Zn supplementation on Cd accumulation in cells, Cd-induced superoxide anion (O(2)(-)) and hydrogen peroxide (H(2)O(2)) production. Zn caused 1.2-2.0-fold inhibition of Cd accumulation, 1.2-2.0-fold inhibition of Cd-induced apoptotic cell death, 1.1-2.0-fold decrease in reactive oxygen species (ROS) production in HeLa cells and in BAECs. These results indicate that inhibition of Cd-induced apoptosis in cells by Zn might be due, not only by inhibition of Cd accumulation in cells but, at least in part, to inhibition of Cd-induced production of ROS, which in turn are known as strong inducers of apoptosis.

The influence of cadmium and zinc ions on the interferon and tumor necrosis factor production in bovine aorta endothelial cells

The influence of CdCl(2), used at 1, 10 and 100 microM concentration, and ZnCl(2) at 1, 10 and 100 microM concentration on the production of interferon (IFN) and tumor necrosis factor (TNF) in bovine aorta endothelial cells (BAECs) was examined. BAECs were treated with cadmium ions or zinc ions alone or together with cytokine inducers: Newcastle disease virus (NDV) and lipopolysaccharide (LPS). Cadmium ions at 1 and 10 microM concentration, used alone induced a low, but detectable TNF activity in BAECs, and zinc ions at 1, 10 and 100 microM concentration induced both IFN and TNF activity. In contrast to that, cadmium added to BAECs together with the virus or LPS as cytokine inducers significantly inhibited the production of IFN and TNF. Cadmium effect depended on the concentration used, and 1 and 10 microM CdCl(2) partially, but 100 microM cadmium completely inhibited the production of both cytokines. Zinc ions at 1 and 10 microM concentration, which only slightly inhibited the production of both cytokines, did not reconstitute cadmium-depressed IFN and TNF production. These data indicate that cadmium-induced depression of cytokine production in bovine endothelial cells, in response to viral and bacterial stimuli, cannot be reversed by zinc supplementation.

Serum concentrations of sIL-2R, IL-6, TGF-beta1, neopterin, and zinc in chronic hepatitis C patients treated with interferon-alpha

T lymphocytes and immunoregulatory cytokines play an important role in the host response to hepatitis C virus (HCV) infection. Zinc is required for a wide spectrum of immune functions, including T-cell activity. To determine the clinical significance of the cytokines sIL-2R, IL-6, TGF-beta1, neopterin, and of zinc in chronic heptatitis C virus (HCV) infection, we investigated their concentrations in the serum of 16 patients with chronic HCV infection before, during and at the end of therapy with interferon (IFN) alpha (Roferon A), and after 6 months follow-up. Elevated concentrations of sIL-2R, IL-6, TGF-beta1, and neopterin were found in the serum of all patients prior to therapy, as compared to healthy controls. sIL-2R patterns differed in responders and non-responders. While the mean concentration of sIL-2R (335.75 pg/ml) before therapy was about 40% higher in complete responders (n=4) than in controls (272.20 pg/ml), the mean concentration in non-responders (n=6) was 4-fold higher than in controls (1153.33 pg/ml). During therapy, sIL-2R levels in responders decreased by about 40%. Mean IL-6 concentrations in both complete and partial responders (n=6) decreased continuously during treatment, while mean concentrations in non-responders decreased for only a short time, and increased again after cessation of therapy. Mean levels of TGF-beta1 behaved similarly to those of IL-6. Only negligible differences in mean neopterin levels were found between responders and non-responders over the entire observation time. The mean serum zinc concentrations slightly decreased in all 3 patient groups, the greatest reduction occurring in 3 of the 4 responders. The present findings underscore the importance of the immune system in the pathogenesis of chronic HCV infection. Serum sIL-2R levels may be used as a serological marker of outcome following IFN-alpha treatment.

Inhibition of apoptosis by ionomycin and zinc in peripheral blood mononuclear cells (PBMC) of leprosy patients

PBMC from tuberculoid (BT/TT) and lepromatous leprosy (BL/LL) leprosy patients showed spontaneous apoptosis when cultured in the absence of mitogen for 24 h, which was inhibited by anti-tumour necrosis factor-alpha (TNF-alpha) antibodies. Apoptosis was also inhibited by ionomycin and zinc, which also increased IL-2 and decreased TNF-alpha production. The increase in IL-2 production suggests a mechanism whereby dietary supplements with zinc might alter the cell-mediated immunity response in leprosy patients.

Zinc status in patients with alveolar echinococcosis is related to disease progression

Zinc is an essential trace element for immune function that plays a role in immune response against parasites. To determine a possible relationship between zinc level and disease status in alveolar echinococcosis (AE), we investigated serum concentrations of zinc, immunoglobulin (Ig)E, IgG, and C-reactive protein (CRP) in 40 AE patients and 20 controls. Patients were classified into three groups: group A: patients after curative surgery, group B: patients with stabilized disease, group C: patients with progressive disease. Patients showed significantly higher levels of IgE and IgG than controls. Amounts of IgE and IgG were related to disease severity, achieving highest levels in group C and lowest in group A. Zinc levels were comparable in patients and controls. However, there was an obvious association between zinc concentration and disease severity. Zinc was far below the normal range in group C (median 9.2 micromol/l) and significantly diminished compared to group B and controls. An inverse pattern was seen for CRP. In conclusion, lowered zinc concentration in progressive cases may be caused by enhanced immune activation but consumption of zinc by the growing parasite may also play a role. Furthermore, decreased zinc levels may contribute to the observed immunosuppression in AE.

Micronutrient supplementation in the AIDS diarrhoea-wasting syndrome in Zambia: a randomized controlled trial

OBJECTIVE

As HIV has spread through sub-Saharan Africa, persistent diarrhoea has emerged as a major problem in hospitals and in the community in severely affected areas. We have previously demonstrated that antiprotozoal therapy with albendazole reduces diarrhoea in AIDS patients in urban Zambia. This trial was designed to test the hypothesis that the clinical response to albendazole might be improved by oral micronutrient supplementation.

DESIGN

Randomized, placebo-controlled trial.

SETTING

Home care service of Ndola Central Hospital, Zambia.

PATIENTS

HIV-seropositive patients with persistent diarrhoea.

INTERVENTION

Patients were randomized to albendazole plus vitamins A, C and E, selenium and zinc orally or albendazole plus placebo, for 2 weeks.

MAIN OUTCOME MEASURES

Time with diarrhoea following completion of treatment; mortality; adverse events.

RESULTS

Serum vitamin A and E concentrations before treatment were powerful predictors of early mortality, but supplementation did not reduce time with diarrhoea or mortality during the first month, even after taking into account initial vitamin A or E concentrations, CD4 cell count or clinical markers of illness severity. Serum concentrations of vitamins A and E did not increase significantly in supplemented patients compared with those given placebo, and there were no changes in CD4 cell count or haematological parameters. No adverse events were detected except those attributable to underlying disease.

CONCLUSIONS

Although micronutrient deficiency is predictive of early death in Zambian patients with the diarrhoea-wasting syndrome, short-term oral supplementation does not overcome it nor influence morbidity or mortality.

The prevention and treatment of cutaneous injury secondary to chemical warfare agents. Application of these finding to other dermatologic conditions and wound healing

Chemical warfare agents are easily and inexpensively produced and are therefore potentially accessible to even underdeveloped nations and are a threat to civilian populations as well as advancing troops. Sulfur mustard is by far the most significant chemical warfare agent that produces cutaneous injury. Significant advances over the past few years have been made in understanding the pathophysiology of the lesions produced by sulfur mustard, as well as development of barrier creams and pre and post exposure therapies to moderate the damage and accelerate healing. Not only have these advances improved our understanding of the sulfur mustard injury and the care of the patients, these are potentially numerous applications for these findings in other dermatologic conditions including the treatment of chronic wounds.

In vitro modulation of keratinocyte wound healing integrins by zinc, copper and manganese

Although the trace elements zinc, copper and manganese are used in vivo for their healing properties, their mechanism of action is still only partially known. Some integrins expressed by basal layer keratinocytes play an essential part in healing, notably alpha2beta1, alpha3beta1, alpha6beta4 and alphaVbeta5, whose expression and distribution in epidermis are modified during the re-epithelialization phase. This study demonstrates how the expression of these integrins are modulated in vitro by trace elements. Integrin expression was studied in proliferating keratinocytes in monolayer cultures and in reconstituted skin that included a differentiation state. After 48 h incubation with zinc gluconate (0.9, 1.8 and 3.6 microg/mL), copper gluconate (1, 2 and 4 microg/mL), manganese gluconate (0.5, 1 and 2 microg/mL) and control medium, integrin expression was evaluated by FACScan and immunohistochemistry. Induction of alpha2, alpha3, alphaV and alpha6 was produced by zinc gluconate 1.8 microg/mL in monolayers, of alpha2, alpha6 and beta1 by copper gluconate 2 and 4 microg/mL and of all the integrins studied except alpha3 by manganese gluconate 1 microg/mL. Thus, alpha6 expression was induced by all three trace elements. The inductive effect of zinc was particularly notable on integrins affecting cellular mobility in the proliferation phase of wound healing (alpha3, alpha6, alphaV) and that of copper on integrins expressed by suprabasally differentiated keratinocytes during the final healing phase (alpha2, beta1 and alpha6), while manganese had a mixed effect.

Zinc, T-cell pathways, aging: role of metallothioneins

Zinc is an essential trace element for many biological functions, including immune functions. Indeed zinc is required for the biological activity of a thymic hormone, called thymulin in its zinc-bound form, important for the maturation and differentiation of T-cells. With advancing age zinc, thymic functions and peripheral immune efficiency show a progressive decline. Supplementing zinc in old age restores them. Zinc is also relevant for liver extrathymic T-cell pathway, being preeminent in old age. Since zinc is also required for metallothioneins (MTs) biological functions, binding zinc with high affinity, aim of the present article is to summarize findings from our laboratory regarding the role of zinc on T-cell pathways, investigating also the possible cause of thymic involution and impaired liver extrathymic T-cell pathway in aging. Partial hepatectomy and liver regeneration are good models for this aim because of the likeness with aging for many immune functions, including thymic functions. MTs levels are increased, other than into the liver, also into the thymus during aging and in young hepatectomized (pHx) mice as compared to young sham controls. MTs may be one of the possible causes of reduced thymic efficiency and impaired liver extrathymic T-cell pathway in old age because of their higher zinc binding affinity rather than thymulin with consequent reduction of the free quota of zinc available for normal cell-mediated immunity. Following that, MTs may contribute to thymic involution and impaired peripheral immune efficiency in aging and in young pHx mice with different roles during the whole life of an organism: protective in young-adult age which may became, at least, dangerous for immune responses in aging. In order to limit or avoid this latter MTs possible role in aging, supplementing physiological zinc may be useful to improve immune responses in old age because of no interference of endogenous zinc on already high thymus MTs levels, but with caution for competition phenomena with copper, as documented in old mice and in syndrome of accelerate aging.

Stress enhanced reduction in peripheral blood lymphocyte numbers in dairy cows during endotoxin-induced mastitis

Two groups of Holstein dairy cows, which showed either high- (HC; n = 8) or low (LC; n = 10) plasma cortisol concentrations in response to a psychological stressor (novel-environment test) in their first lactation, were used 1 year later for studying the effects of psychological stress on various aspects of the host defence during endotoxin-induced mastitis. Social isolation was used as a stressor; endotoxin was used to activate the host defence. HC-cows appeared to be more stressed by the experimental procedure than LC-cows. One hour after having been isolated, rectal temperature increased (+0.59 degrees C) in HC- but not in LC-cows. Handling, related to the intra-mammary administration of endotoxin, induced a higher increase in cortisol concentration in HC- than in LC-cows 1 h after injection. In addition, HC-cows vocalised significantly more frequently (595 +/- 222) than LC-cows (81 +/- 24) between 1.5 and 9.5 h after isolation. Between 3 and 5.5 h after endotoxin-treatment, cortisol concentrations increased profoundly in both LC- and HC-cows and peaked at 24.6 +/- 3.8 and 22.8 +/- 3.1 ng ml(-1), respectively. The rise in plasma cortisol concentration was associated with a decrease in the number of circulating lymphocytes between 0 and 8 h post injection (PI). Between 8 and 10 h PI, the number of circulating lymphocytes in HC-cows further decreased (40%) to 1.58x10(6) cells ml(-1) and remained so until 21 h PI. This was not the case with the LC-cows. The results show that a differing sensitivity of dairy cows to environmental stressors is associated with a significant difference in the number of circulating leukocytes following intra-mammary administration of endotoxin during a period of social isolation. The results further suggest that, apart from adrenocortical hormones, other factors related to general stress-responsiveness modulate the number of peripheral lymphocytes in dairy cows during endotoxin-induced mastitis. During environmental stress, these factors may enhance endotoxin-induced reduction in circulating lymphocyte numbers, particularly in cows that are sensitive to environmental stressors. As to the clinical relevance of these differences in stress responsiveness, no differences between LC- and HC-cows were found in disease incidence nor in duration of a disease episode during both the 1st and 2nd lactation. In the 2nd lactation. HC-cows tended to produce less milk than LC-cows.

Tissue zinc dynamics during the immune reaction in mice

Owing to the importance of zinc for the functioning of the immune system, the role of endogenous Zn, located both in lymphoid and nonlymphoid organs, was investigated during the standard humoral and cellular types of immune response. For this purpose, the dynamics of hepatic, thymic, splenic, and renal Zn content was determined in mice sensitized with (a) sheep red blood cells and (b) semiallogeneic lymphocytes during the local host vs graft reaction (HVGR). The data obtained by ion-coupled plasma spectrometry revealed that the humoral type of immunity is characterized by a significant increase of Zn concentration in the liver and in the thymus. Simultaneously, linear regression analysis showed that the generation of plaque-forming cells in the individual mouse was highly positively correlated with Zn concentration in the liver (r=0.897), and spleen (r=0.833), and negatively with Zn concentration in the thymus (r=-0.624). Similar relationships between the intensity of local immune reaction and tissue Zn levels were found in local HVGR at the fifth day in the liver and spleen (r=0.861 and r=0.695, respectively), at the seventh day in the thymus (r=-0.797), and at the tenth day in the liver (r=-0.859). The data emphasize the necessity of Zn for the development of normal immune response and point to the existence of a Zn-dependent hepato-thymic axis during the humoral and cellular types of immune reactivity.