In addition to the effect of trace elements on immune function, recent studies from Beck et al. (1995) have demonstrated that selenium (Se) levels can influence the genetics of a viral pathogen. Thus, trace element nutrition influences not only the host response to a pathogen but also the pathogen itself.
This paper reviews the effect of the trace minerals zinc (Zn), copper (Cu), and Se on immune function, as well as the effect of Se on a viral pathogen. Implications for soldiers in the field will also be discussed.
Zn is perhaps one of the most studied trace elements with respect to its effect on the host immune system. Deficiencies in Zn have been classified into three syndromes by Henkin and Aamodt (1983): acute, chronic, and subacute deficiency. It has been suggested that subacute deficiency is the most common, affecting an estimated 4 million people in the United States (Walsh et al., 1994). Zn is obtained in the diet primarily from meat (50%), cereals and legumes (30%), and dairy products (20%) (USDA, 1986).
Zn deficiency has been noted to result in increased susceptibility to infectious disease (Bogden et al., 1988). In a mouse model of Zn deficiency (Fernandes et al., 1979; Fraker et al., 1978, 1986), a 30-d feeding period of suboptimal levels of Zn led to reduced thymus size and depleted macrophages and lymphocytes in the spleen. Suboptimal Zn status has also been associated with decreased T-cell function and antibody responses (Kruse-Jarres, 1989). If the Zn deficiency is corrected, immune status is restored (Walsh et al., 1994).
Excess levels of Zn have also been reported to be immunosuppressive, including decreased activities of polymorphonuclear leukocytes, decreased T-cell proliferation to mitogen, and decreased antibody production (Schlesinger et al., 1993). Thus, Zn status, both excess and deficient, adversely affects immune function.
Singh et al. (1994) found that supplemental Zn given prior to strenuous exercise reduced the amount of reactive oxygen species that occur post exercise. This antioxidant effect of Zn may be of importance to troops who are under chronic physical stress.
Driessen et al. (1995) found that, in vitro, lipopolysaccharide-stimulated peripheral blood mononuclear cell cultures exposed to 0.0125 mM Zn had elevated interleukin (IL)-1β levels that were 50 percent higher than cultures that were not supplemented with Zn. Secretion of interferon-gamma (INF-γ) increased 10-fold when cultures were supplemented with 0.1 mM Zn. However, monocyte stimulation by superantigens (staphylococcal enterotoxins A and E) was decreased in cultures supplemented with Zn. Thus, depending on the type of stimulus, supplemental Zn may exert different effects.
Zinc is a cofactor for a number of enzymes, including thymidine kinase, ribonuclease, and RNA and DNA polymerases. All of these enzymes are