Resistance and susceptibility to infection in inbred murine strains. IV. Effects of dietary zinc

An alloy of zinc and innate immunity: Galvanising host defence against infection

Innate immune cells such as macrophages and neutrophils initiate protective inflammatory responses and engage antimicrobial responses to provide frontline defence against invading pathogens. These cells can both restrict the availability of certain transition metals that are essential for microbial growth and direct toxic concentrations of metals towards pathogens as antimicrobial responses. Zinc is important for the structure and function of many proteins, however excess zinc can be cytotoxic. In recent years, several studies have revealed that innate immune cells can deliver toxic concentrations of zinc to intracellular pathogens. In this review, we discuss the importance of zinc status during infectious disease and the evidence for zinc intoxication as an innate immune antimicrobial response. Evidence for pathogen subversion of this response is also examined. The likely mechanisms, including the involvement of specific zinc transporters that facilitate delivery of zinc by innate immune cells for metal ion poisoning of pathogens are also considered. Precise mechanisms by which excess levels of zinc can be toxic to microorganisms are then discussed, particularly in the context of synergy with other antimicrobial responses. Finally, we highlight key unanswered questions in this emerging field, which may offer new opportunities for exploiting innate immune responses for anti-infective development.

Effect of oral zinc supplementation upon Taenia crassiceps murine cysticercosis

The effect of zinc supplementation on Taenia crassiceps murine cysticercosis was studied in susceptible BALB/cAnN mice. Female offspring of mice supplemented with high zinc throughout gestation and lactation were intraperitoneally infected with T. crassiceps cysticerci. Offspring from nonsupplemented mothers were used as controls. Significantly fewer parasites were recovered from zinc-supplemented mice (Zsm) 30 days after infection. Increased resistance was not related to the IgG antibody response. At early stages of infection, T cells from Zsm proliferated to T. crassiceps antigens, whereas cells from control mice did not respond. Infection caused in both groups a decrease in CD3+ cell percentages, which was more pronounced in the controls, and paralleled by a decrease in CD8+ cells; CD3+ and CD8+ percentages returned to normal levels at later stages of infection. In contrast, the CD4+ subpopulation only decreased in control mice. Intracellular cytokine determinations indicate that zinc supplementation favored a stronger and persistent type-1 T cell response in cysticerci-infected mice, which probably participates in the observed increased resistance.

Zinc deficiency impairs immune responses against parasitic nematode infections at intestinal and systemic sites

Research on the complex interactions among host nutritional status, parasitic infection and immune responsiveness has focused on the detrimental consequences of parasitic infections on host nutritional status and on mechanisms by which malnutrition impairs immunocompetence. Curiously, relatively few studies have examined the effects of malnutrition on the immune response in the parasite-infected host, and even fewer have considered the events occurring at the intestinal level, where absorption of nutrients occurs, intestinal parasites reside, and the gastrointestinal-associated lymphoid tissues play a role in directing both the local and the more systemic immune responses. Our work using a zinc-deficient nematode-infected mouse model reveals that parasites are better able to survive in the zinc-deficient hosts than in well-nourished hosts; that the production of interleukin-4 in the spleen of zinc-deficient mice is depressed, leading to depressed levels of IgE, IgG(1) and eosinophils; and that the function of T cells and antigen-presenting cells is impaired by zinc deficiency as well as by energy restriction. Given the paramount role of the gastrointestinal-associated lymphoid tissues in inducing and regulating immune responses to intestinal parasites and in orchestrating responses in the spleen and peripheral circulation, we conclude that zinc deficiency (in association with energy restriction) exerts profound effects on the gut mucosal immune system, leading to changes in systemically disseminated immune responses and, importantly, to prolonged parasite survival.

Advances in the role of minerals in immunobiology

Immunology and our understanding of its various cells, immunoglobulins and lymphokines are recent events that date from the work of Pasteur and Metchnikoff in the late nineteenth century. Experimental evidence has shown the importance of adequate dietary protein and vitamins. The present review examines past and recent experimental evidence for the role of minerals in the functioning of the immune system. Included is in vivo and in vitro information on the macrominerals; calcium and magnesium, the micro-(trace) minerals; iron, zinc, copper, and selenium as they affect various components of the immune system. The effects of gold as either gold-thiomaleate or gold-thioglucose on selenium is also reviewed.

Zinc status, pregnancy complications, and labor abnormalities

Maternal plasma zinc levels, red blood cell levels, and serum alkaline phosphatase activity were used as indices of zinc status in 279 pregnant women at delivery and were compared with the incidence of complications during the antenatal period and major dysfunctional labor patterns. The median values for plasma zinc, red blood cell zinc, and alkaline phosphatase were used as cutoff points to subdivide the patient population into "low" and "high" groups. Low levels of maternal plasma zinc were associated with more complications in the antenatal or intrapartum periods than maternal levels of either alkaline phosphatase or red blood cell zinc. Plasma zinc levels less than the median value were more commonly associated with mild toxemia (p = 0.02), vaginitis (p = 0.01), and postdates (p = 0.01) in the antenatal period. During the intrapartum period, low plasma zinc levels were associated with a prolonged latent phase (p = 0.05), a protracted active phase (p = 0.04), labor greater than 20 hours (p = 0.03), second stage greater than 2.5 hours (p = 0.01), and cervical and vaginal lacerations (p = 0.02). Low levels of maternal alkaline phosphatase were strongly associated with a history of previous stillbirth (p = 0.0005). A low maternal red blood cell zinc level was not associated with complications during either period. Since a low plasma zinc level is a valid predictor of pregnancy complications and abnormal labor, the results suggest that plasma zinc screening, as part of the patient's antenatal workup should be evaluated.

The effect of dietary zinc and prothymosin alpha on cellular immune responses of RF/J mice

Mice of the RF/J strain on a normal diet are defective in some aspects of cellular immunity, as evidenced by their susceptibility to infection with Candida albicans, their failure to release detectable quantities of circulating migration inhibitory factor (MIF) in vivo, and the presence of a low rate of phagocytosis and killing by peritoneal macrophages. When the mice were fed a high-zinc diet (300 ppm) for 4 weeks and then treated daily with 160 ng prothymosin alpha, an increase occurred in resistance to infection with C. albicans, in the capacity to release MIF in vivo into the circulation and in the capacity of peritoneal macrophages to engulf (phagocytose) and kill cells of C. krusei. In addition, the number of spleen lymphocytes producing antibody to a T-dependent antigen was significantly increased in the mice fed a high-zinc diet and inoculated daily with prothymosin alpha.

Zinc status in women with recurrent vulvovaginal candidiasis

Zinc status has been shown to influence various cell-mediated immunologic mechanisms. These cell-mediated mechanisms are important in preventing mucocutaneous infections caused by Candida albicans. This study evaluated the relationship between zinc status and recurrent vaginal candidiasis by comparing plasma and erythrocyte zinc in 29 patients with recurrent vaginal candidiasis and 20 control subjects matched for age, race, and parity. The results indicated that there was a significantly lower level of plasma zinc in women with recurrent vaginal candidiasis (81 + 11.6 mg/dl) than in the control subjects (91 +/- 14.2 mg/dl) with a significant value of p = 0.015. These differences in plasma zinc levels were even greater when adjusted for dietary zinc and supplemental zinc with the use of analyses of covariance. No differences in erythrocyte zinc measurements were found between the two groups. These results suggest that mild zinc deficiency is associated with recurrent vaginal candidiasis and may play a role in the susceptibility of women to recurrent vaginal candidiasis.

T-lymphocyte subsets and interleukin-2 production in zinc-deficient rats

1. It has been suggested that zinc-deficiency impairs cellular (T-lymphocyte-mediated) immune responses via a selective effect on helper T-lymphocytes. We have addressed this question in the rat by employing recently developed reagents in the form of monoclonal antibodies which specifically identify rat T-lymphocyte subsets (identifying total T-cells, helper T-cells and suppressor T-cells) and also by quantifying helper T-cell function by measurement of the helper T-cell-derived molecule interleukin-2 (IL-2). 2. Zn-deficiency induced T-cell atrophy (assessed morphologically and phenotypically with anti-rat T-cell monoclonal antibodies) in both peripheral blood and spleen. The use of these specific monoclonal antibodies failed to demonstrate a selective effect of Zn deficiency on the helper T-cell fraction of the total T-lymphocyte population. 3. In contrast, the results of functional assays of the T-lymphocyte response were dependent on the conditions of culture but suggested that the generation of IL-2 and its corresponding receptor were determined by the intracellular Zn status. Thus, in vivo, helper T-lymphocyte numbers are non-specifically reduced since other T-cell subsets are also reduced in response to appropriate stimulation. The functional consequences of this are dependent on the intracellular concentration of Zn but appear to influence both IL-2 production and its receptors on activated T-cells.