Our immune system is the most dynamic body component in determining our state of health or disease. It will be the basis, I believe, of future breakthroughs in medicine. There is a great deal of evidence from current and past research demonstrating life’s effects on human immune function and our immune system’s influences upon our health. These investigations provide a continuous flood of knowledge about the sensitive balance and many levels involved in our wellness. Psychoneuroimmunology, which provides a bridge between psychology and the nervous and immune systems, now plays an essential role in medicine.

Our immune system constantly interacts with our internal environment, protects us from our external environment, and provides the inherent knowledge to sense the difference between friend and foe. For many reasons, including genetics and individuality, some of us may be overactive or too underactive in our defenses, and this can create a great variety of health problems, such as allergies, infections, and cancer.

There are many components to our immune system—organs, bone marrow, cells, antibodies, chemicals, and the nutrients that help nourish and generate them. Most of these cells and tissue constituents are part of what is called in medicine the reticuloendothelial system, which plays a "defensive role in inflammation and immunity" (Dorland’s Medical Dictionary) and in the formation and destruction of blood cells. Our immune system protects us from viruses, bacteria, yeasts and fungi, foreign proteins, and cancer cells. It provides two kinds of protection: Innate (inborn) nonspecific immunity and specific learned or acquired immunity. Specific immunity depends on "humoral" (antibodies and chemicals carried in the blood) and cellular (white blood cells) responses, which can be immediate or delayed.

The thymus-derived lymphocytes (T lymphocytes or, simply, T cells) run the cellular defense and the delayed immune reactions. T cells, specifically T-helper lymphocytes, guide the B cells to produce antibodies (each cell produces only one specific antibody), a process that takes a three-to-five or more days induction period, often the time of infection by new viruses. Reexposure to the same virus will create a more rapid antibody response. This is our important immune memory and there are "memory B cells" that circulate in the blood to respond to subsequent infections. The T-helper cells stimulate immune activity, especially B cell activity, whereas the T-suppressor cells slow down certain functions such as antibody formation, usually after a problem has been handled. Another important cell which is neither a T or B cell or a phagocyte is the NK (natural killer) cell. The T lymphocytes also send messages to (and receive messages from) the macrophages and other phagocytes to "attack" virus-infected cells and foreign organisms, either by engulfing or marking them. Other T cells can also be cytotoxic to virus-infected cells. All of these important T lymphocytes originate in the bone marrow and mature in the thymus gland, the "king" of the immune system. B lymphocytes also originate in the bone marrow and may mature there, in the spleen, lymph nodes, and elsewhere; they are programmed to become the antibody factories or the plasma cells, which are formed from B cells and also produce the specific antibodies.