Boosting the Immune System

  White blood cells, or leukocytes, are the immune system's first line of defense, moving quickly to the site of an injury or infection. Each category of white blood cells performs a specific function.

  Monocytes, the largest cells in the blood, act as "garbage collectors." They engulf and digest foreign particles, as well as damaged or aging cells. Neutrophils are the most abundant type of white blood cell; their function is to ingest and destroy microorganisms. Eosinophils ingest and destroy antigen-antibody combinations, while basophils secrete histamine or heparin in response to contact with antigens.

  Lymphocytes play the central role in the immune system, and are responsible for the development of specific immunities. The three major groups of lymphocytes are B cells, responsible for the production of antibodies; T cells, which play a major role in cell-mediated immunity; and null cells, which destroy cells that have become infected or cancerous.

  The immune system identifies and remembers specific antigens via two methods: cell-mediated immunity and humoral immunity. In cell-mediated immunity, T cells help identify and destroy cancerous cells, viruses and microorganisms such as bacteria and fungi. The cells are termed "T" because after being generated by bone marrow stem cells, they migrate to the thymus gland, where they are programmed to identify particular types of immunogens. T cells do not produce antibodies; rather, they attack various abnormal cells, including cancer cells and host cells that have been taken over by viruses or other microorganisms. T cells also attack antigens by secreting mediator proteins called lymphokines, which are not immunologically specific, but which function to regulate the immune system.

  Humoral, or antibody-mediated immunity, involves the production of antibodies, which are also known as immunoglobulins. These glycoproteins are produced in response to antigens, and have specific antigen-combining sites that correspond to the chemical structure of invading substances. When B cells encounter an antigen, they produce antigen-specific antibodies, thereby "remembering" the chemical structure of invading cells so that upon the next exposure, the body can launch its defense immediately.

  Immune boosters are particularly important for those who are HIV positive, notes Raphael B. Stricker, M.D., director of the Cellular Immunity Foundation, San Francisco. But a healthy immune system is critical for everyone, and immune-system enhancement is also a potential option for less critical conditions such as colds and flu.

  Several herbs, dietary supplements and food components have been linked to an increase in immune function. Research is still underway to help determine precisely how these compounds work, but early evidence is promising, suggesting that immune boosters derived from plant sources may prove very beneficial in helping maintain health.

  Known as the king of blood purifiers, echinacea (E. purpurea) helps improve lymphatic filtration and drainage. It is also thought to help remove foreign substances by stimulating phagocytosis and the production of immune-response compounds. Although most frequently used as an energy booster, ginseng also appears to stimulate cellular immune function.

  In a study published in the January 1997 Immunopharmacology, researchers found that extracts of both ginseng and echinacea enhanced the immune response of healthy subjects and those with either chronic fatigue syndrome or AIDS. The extracts also increased antibody-dependent cytotoxicity, or the ability of the immune system to destroy infected targets.

  Astragalus root, which is effective in treating digestive ailments, is also thought to inhibit tumor spreading, as well as boost resistance to colds and flu, perhaps by increasing the number of stem cells in bone marrow and lymph tissue, then stimulating differentiation of these cells into immune-competent cells.

  It should be noted that although certain treatments appear to be excellent therapy for those with compromised immune function, extended (over two weeks) use of immune boosters is not recommended for otherwise healthy individuals suffering from a cold or the flu.

  Found in yogurt and other cultured dairy products, friendly bacteria such as Streptococcus thermophilus and Lactobacillus bulgaricus have been noted for their beneficial effects in the intestinal tract, but probiotics such as these are also believed to boost the immune system by increasing the activity of phagocytes, the cells that ingest dead and invading cells.

  Finally, preliminary evidence suggests that maritime pine bark extract may act as a modulator of the macrophage immune response by regulating nitrogen monoxide production, although most research thus far has focused on whether it can reduce memory loss, inhibit platelet aggregation and improve circulation. This extract from the tree Pinus maritima is marketed as Pycnogenol® and contains a number of antioxidant bioflavonoids, particularly procyanidins consisting of catechin and epicatechin units.

  The immune system is incredibly complex, and further research is sure to contribute to our understanding of how the body's defense system fights invaders, and how certain substances may be able to help that system along. In the meantime, it's good to know that our built-in immune system is incredibly effective - even if it does get a little confused about ragweed pollen and cat dander from time to time.

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