Immunity and health
When we ask ourselves the question "What is health?" we are usually faced with a wide range of answers, each as bewildering as the next.
If fitness is not health, we feel that there is a hidden truth behind this idea. The fitness of the immune system is an integral part of our health. Without an active immune system, cellular defences (the white blood cell system that protects us) are dormant. It is therefore on the reawakening of the cellular defence mechanisms that scientists have turned their attention and are now focusing. The extreme increase in the rate of cancers of all types has required innovation, invention and investment in deepening our knowledge of immunity. It has become imperative to create practical methods to help and improve immune function.
Our level of immunity, i.e. the way our immune system is activated, depends on the quality and quantity of nutrients in our diet, as well as the amounts of pollutants in our body. People with weak or slow immune systems are more likely to develop diseases, including cancer, because the body is less able to defend itself against them. When the strength of the immune system depends on external factors, such as diet and pollution, most cancers have an environmental agent as a trigger.
Natural killer cells or NK cells are an essential component of our immune defences. This type of white blood cell or lymphocyte is produced in the bone marrow (as are other types of lymphocytes such as T and B cells) and the mature cells with the T cell in the thymus gland. The production of these defence cells increases in the presence of tumour cells.
Of all the gatekeepers of the immune system, NK cells are the most aggressive (acronym for natural killer). They are the backbone of the immune system and our first line of defence against mutant and virus-infected cells such as tumour cells and the recent Severe Acute Respiratory Syndrome (SARS), which threaten our health.
Natural killer cells are lymphocytes without immunological memory and are part of our innate immune system. This means that they act by pure instinct, programmed to destroy infected and cancerous cells. These cells represent about 5-16% of the total lymphocyte population and are totally dedicated to this search and destroy mission.
However, NK cells do not kill indiscriminately. They look for a "banner" displayed by normal cells and, if they find that banner, they will avoid that kind of cell. This signal overrides the strong urge of NK cells to kill. If this banner is absent on the target cell, the NK cell attacks: it binds to the target and releases a lethal dose of chemicals that penetrate the cell wall. Fluids begin to seep in and out and, in this case, the cell explodes.
NK cell destroying tumour cells
After leaving the bone marrow, NK cells most often accumulate in the secondary lymphoid tissues - the tonsils, lymph nodes and spleen. There, these NK cells await activation (probably after stimulation by sentinel dendritic cells) before reacting in one of two ways. Either they rapidly secrete cytokines, chemical messenger proteins that modulate T and B cell responses, or NK cells become potent killers of virus-infected cells. Although NK cells provide a crucial initial defence against many infectious agents and tumour cells, they do so more by discrimination than by sheer determination.
However, NK cells do not always succeed in detecting tumour cells. These undetected tumour cells may lack antigenic properties that normally provoke the immune system, or the suppressor lymphocytes may hinder the NK cell assault. NK cells have a major role in the immune system, attacking cancer. NK cells are also suppressed by chronic diseases, such as chronic viral diseases. Therefore, a wider range of factors should be considered in a cancer patient than just the number of NK cells.
Studies have shown that patients with persistent malignancy and large tumour masses have decreased NK cell activity. Low NK cell activity is significantly associated with the development of metastases. In patients with metastatic disease, life span is directly related to the level of NK cell activity.
By removing a primary tumour, potential malignant cells can be recirculated and develop into secondary metastatic sites. In addition, the repressive effects of surgery and anaesthesia on NK cell activity may facilitate the survival of tumour cells released from the growth of the primary or metastatic tumour and contribute to an increased incidence of metastasis.
NK cell destroyed tumour cell
Radiotherapy and chemotherapy will reduce NK cell activity, so it is important to reduce the adverse effect on the immune system. Low NK cell activity also occurs in autoimmune diseases and in chronic fatigue syndrome. Of great concern is the fact that many common chemicals alter, weaken and decrease NK cell function and numbers.
Biological response modifiers can increase the activation, proliferation or cytotoxicity of pre-existing NK cells. Cytokines - such as IL2 and IL12 interferons -, bacterial products, plant lectins and extracts, coriolus versicolor, medicinal fungi, transfer factor and antioxidants, such as vitamin C, all have a function in improving immune function.
In addition, there are calls for efforts to overcome the repressive effects of surgery and anaesthesia on NK cell activity. This repression may, in addition, facilitate the survival of tumour cells released from primary or metastatic tumour growth and contribute to the increased frequency of metastasis. Therefore, low doses of interferons and the complementary use of plant extracts may be safe and, with appropriate treatment, effective in preventing tumour development and metastasis.
Activation of NK cells can be easily achieved by treatment with interferon, interferon inducers, interleukin-2 and bacterial adjuvants.