Immunology and Cancer
The immune system is extremely intricate and finely tuned. If any one aspect of the system malfunctions because of poor nutrition, or if it is destroyed, you may become susceptible to cancer and foreign microbial invaders. The white blood cell army and the antibody army must be functioning perfectly to destroy any cancer cell or foreign invader and prevent either one from gaining a foothold in your body.

The major histocompatibility complex is part of your genetic makeup and is another component of the immune system, acting as a commander of the white blood cell and antibody armies. This complex allows the immune system to recognize the parts of your body so that it does not destroy them as it would destroy foreign substances. At the same time, it can recognize a substance or tissue (histo-) as not belonging to its body and subsequently take the necessary steps to destroy it. The histocompatibility complex is responsible for rejection of transplanted organs such as kidneys and hearts. If the histocompatibility complex is not working properly, a virus capable of converting normal cells to cancer cells may enter the body without being attacked because the immune system did not recognize it as foreign. The virus, if not destroyed, will convert normal cells to cancer cells in a process called transformation, and the cancer will multiply and eventually kill the person.

In 1970, F.M. Burnet introduced the concept of immunosurveillance, which states that killer cells of the immune system watch, or keep a surveillance on, all cells in the body and immediately destroy any cells that start to have a malignant or cancerous potential. (6) There is a lot of evidence to support this concept. The most clear-cut and convincing evidence comes from observations of patients with suppressed immune systems caused by drugs or radiation or an inherited disorder. Patients with inherited immunodeficiencies, whose immune systems do not function normally from birth, or patients whose immune systems acquire a malfunction later in life have one hundred times more deaths due to cancer than the expected cancer death rate in the normal population. (7,8) Kidney transplant patients, who receive drugs to suppress the immune system's ability to reject the new kidney, also have a higher rate of cancer than would be expected. (9,10) The cancers most frequently seen in these cases are the Iymphomas and epithelial cancers; however, all other types of cancers have been reported as well.

The immune system is relatively immature in infancy, and then runs down and does not function well in old age. These two times of life have the highest incidence of Iymphocytic leukemia. Other immune-deficiency states that can lead to cancer are seen with malaria, acute viral infections, and malnutrition.

Nutrition and the Immune System
Nutritional deficiencies decrease a person's capacity to resist infection and its consequences and decrease the capability of the immune system. (11) In old age, there is a decrease in skin hypersensitivity reactions, (12,14) a decreased number of T cells, (l5,16) and impairment of some phagocytic functions. Surveys of the population have discovered nutritional deficiencies in senior citizens that also lead to impairment of the immune system. (17) It is possible that the gradual impairment of the immune system associated with aging may, in fact, be due to one or more nutrient deficiencies. Poor nutrition adversely affects all components of the immune system, including T cell function, other cellular-related killing, the ability of B cells to make antibodies, the functioning of the complement proteins, and phagocytic function. When several of these functions or processes are impaired, the ability of the entire immune system to keep a watchful eye for cancer cells, abnormal cells, or foreign substances and to dispose of them is also markedly impaired.