Strength. Protection. Defense. Perseverance. These are the words one thinks of when considering immunity. We all try to keep from getting sick by taking precautions like washing our hands, covering our mouths and, especially, maintaining a healthy diet. Providing the body the right nutrients helps it work 24/7/365 to ward of invaders, called pathogens, be they viral, bacterial, fungal or other biological evil agent.
The immune system is a multilayer masterpiece of barriers—mucosal surfaces, skin and other membranes—and chemical defenders that work together to confront and banish pathogens. Their quest is for balance, as some components promote actions, such as inflammation and apoptosis (cell death), while others counter those actions when the goal is achieved, keeping the system in check. A hyper-stimulated system can lead to autoimmune problems, and a suppressed system can lead to further infection; both can lead to degeneration.
The key mobile components of this system are white blood cells called leukocytes. These include lymphocytes, which include B cells, T cells (T-helper and cytotoxic T cells) and natural killer (NK) cells; monocytes, which become either macrophages (consume pathogens) or dendritic cells (activate T lymphocytes); neutrophils (hunt bacteria and fungi); eosinophils, which target larger parasites; and basophils, which are responsible for releasing histamine.
Untriggered B cells circulate through the lymph system until they are activated in the thymus or by a T cell to produce antibodies (i.e., immunoglobulins), which each specialize in a specific antigen. There are five classes of immunoglobulins: immunoglobulin G (IgG), IgA, IgM, IgD and IgE.
T cells form the foundation of cell-mediated immunity, responding to self-cells that have changed due to a virus or a cellular mutation. Among the various T cell types, cytotoxic T cells cause cell death and attract macrophages for continued consumption of the foreign matter. Helper T cells, known as CD4 or CD8 cells, stimulate the activity of cytotoxic T cells. The two subclasses of CD4 cells are Th1 and Th2, each of which releases interleukins to trigger particular immune functions. Th1 responses activate macrophages to kill pathogens, create inflammation, stimulate antibody production and secrete interleukin-2 (IL-2) and interferon-gamma (IFN-gamma). And, Th2 responses feature high levels of antibody production, including secretion of certain antibodies and production of IL-4, IL-5, IL-10 and IL-30.
In addition to these worker cells, the immune system involves two fluid-like components. Complement is a mixture of proteins and proteases that can trigger production of cytokines that help kill foreign cells in membranes. Lymph is a plasma-like interstitial (between body cells) fluid that contains nutrients and white blood cells, and travels to and from lymph nodes, which are where lymphocytes meet antigens (foreign substances) caught up in the nodes.
The intricate science on immune function is reflected in the recent research on various nutrients and nutraceutical ingredients and their effects on various factors of immune modulation. Immune function is one of the hottest health research categories, with new results coming out every month. What follows is an overview of some such results spanning a variety of ingredients, from micronutrients and plant-based compounds to mother’s milk and live cultures.
The first stop in most dietary interventions is basic nutrients. Vitamins and minerals certainly have shown an impact on mechanisms of immune response. Most people are familiar with vitamin C supplements for cold and flu season—C has been shown to help maintain cellular integrity and improves NK and lymphocyte activity1—but a recent study showed how vitamin D might play a role in survivability during a particularly difficult immune challenge: lymphoma.
Researchers from the University of Iowa/Mayo Clinic Lymphoma Specialized Program of Research Excellence (SPORE), which is funded by the National Cancer Institute (NCI), studied 374 newly diagnosed diffuse large B-cell lymphoma patients, finding half were deficient in vitamin D, based on the widely used clinical value of less than 25 mg/mL total serum 25(OH)D.2 Further, after adjusting for other variables, researchers discovered those with deficient D levels were 1.5-times more likely to experience progression of the disease and twice as likely to die from it than did patients with higher D levels. In the end, lead investigator, Matthew Drake, M.D., Ph.D., an endocrinologist at Mayo Clinic, Rochester, MN, suggested vitamin D supplementation could potentially be a viable treatment option for this and other cancers, pending further investigation.
In other areas of immune health, vitamin D appears to affect signaling within macrophages and keratinocytes in the epidermis, enhancing their responsiveness to barrier defense.3 The other letter nutrients have important roles in immune response. Vitamin A, and its active metabolite retinoid acid, can influence adaptive immunity by increasing antibody response and regulating T/B cell populations and cellular differentiation.4 And vitamin E affects cytokine production, thereby impacting inflammatory response, especially in the elderly.5 In 2009, scientists at Jean Mayer USDA Human Nutrition Research Center, Boston, observed differences in vitamin E’s immune actions are influenced by genes.6
On minerals, zinc functions as an intracellular signal molecule for immune cells.7 Similar to deficiency of vitamin D, a lack of sufficient zinc in the body has been linked to increased production of pro-inflammatory cytokines and oxidative stress.8 On the flip side, normal plasma zinc concentrations correlate to decreased risk of pneumonia.9 Likewise, zinc supplementation (as zinc gluconate) appears to lessen the chances of infection.10
Selenium rounds out the recent mineral research, with deficiency of selenium, especially selenoproteins, having been associated with diminished macrophage activities, according to a 2009 NCI study.11 Chinese Academy of Sciences, Beijing, researchers confirmed the negative effect low selenium levels can have on innate immunity, showing selenium-deficient animals were more not only more susceptible to bacterial infection (Listeria monocytogenes), but also suffered a decreased response to the infection.12