Free Term Paper on Blood and Immunity

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The immune system is composed of many interdependent cell types that collectively protect the body from bacterial, parasitic, fungal, viral infections and from the growth of tumor cells. Many of these cell types have specialized functions. The cells of the immune system can engulf bacteria, kill parasites or tumor cells, or kill viral-infected cells. Often, these cells depend on the T helper subset for activation signals in the form of secretions formally known as cytokines, lymphokines, or more specifically interleukins. The purpose of this article is to review the organs, cell types and interactions between cells of the immune system as a commentary on their importance and interdependence on the T helper subset. Such an understanding may help comprehend the root of immune deficiencies, and perceive potential avenues that the immune system can be modulated in the case of specific diseases.


The Organs of the Immune System


Bone Marrow -- All the cells of the immune system are initially derived from the bone marrow. They form through a process called hematopoiesis. During hematopoiesis, bone marrow-derived stem cells differentiate into either mature cells of the immune system or into precursors of cells that migrate out of the bone marrow to continue their maturation elsewhere. The bone marrow produces B cells, natural killer cells, granulocytes and immature thymocytes, in addition to red blood cells and platelets.

Thymus -- The function of the thymus is to produce mature T cells. Immature thymocytes, also known as prothymocytes, leave the bone marrow and migrate into the thymus. Through a remarkable maturation process sometimes referred to as thymic education, T cells that are beneficial to the immune system are spared, while those T cells that might evoke a detrimental autoimmune response are eliminated. The mature T cells are then released into the bloodstream.

Spleen -- The spleen is an immunologic filter of the blood. It is made up of B cells, T cells, macrophages, dendritic cells, natural killer cells and red blood cells. In addition to capturing foreign materials (antigens) from the blood that passes through the spleen, migratory macrophages and dendritic cells bring antigens to the spleen via the bloodstream. An immune response is initiated when the macrophage or dendritic cells present the antigen to the appropriate B or T cells. This organ can be thought of as an immunological conference center. In the spleen, B cells become activated and produce large amounts of antibody. Also, old red blood cells are destroyed in the spleen.

Lymph Nodes -- The lymph nodes function as an immunologic filter for the bodily fluid known as lymph. Lymph nodes are found throughout the body. Composed mostly of T cells, B cells, dendritic cells and macrophages, the nodes drain fluid from most of our tissues. Antigens are filtered out of the lymph in the lymph node before returning the lymph to the circulation. In a similar fashion as the spleen, the macrophages and dendritic cells that capture antigens present these foreign materials to T and B cells, consequently initiating an immune response.
The Cells of the Immune System
T-Cells -- T lymphocytes are usually divided into two major subsets that are functionally and phenotypically (identifiably) different. The T helper subset, also called the CD4+ T cell, is a pertinent coordinator of immune regulation. The main function of the T helper cell is to augment or potentiate immune responses by the secretion of specialized factors that activate other white blood cells to fight off infection.

Another important type of T cell is called the T killer/suppressor subset or CD8+ T cell. These cells are important in directly killing certain tumor cells, viral-infected cells and sometimes parasites. The CD8+ T cells are also important in down-regulation of immune responses. Both types of T cells can be found throughout the body. They often depend on the secondary lymphoid organs (the lymph nodes and spleen) as sites where activation occurs, but they are also found in other tissues of the body, most conspicuously the liver, lung, blood, and intestinal and reproductive tracts.

Natural Killer Cells -- Natural killer cells, often referred to as NK cells, are similar to the killer T cell subset (CD8+ T cells). They function as effector cells that directly kill certain tumors such as melanomas, lymphomas and viral-infected cells, most notably herpes and cytomegalovirus-infected cells. NK cells, unlike the CD8+ (killer) T cells, kill their targets without a prior "conference" in the lymphoid organs. However, NK cells that have been activated by secretions from CD4+ T cells will kill their tumor or viral-infected targets more effectively.

B Cells -- The major function of B lymphocytes is the production of antibodies in response to foreign proteins of bacteria, viruses, and tumor cells. Antibodies are specialized proteins that specifically recognize and bind to one particular protein that specifically recognize and bind to one particular protein. Antibody production and binding to a foreign substance or antigen, often is critical as a means of signaling other cells to engulf, kill or remove that substance from the body.

Granulocytes or Polymorphonuclear (PMN) Leukocytes -- Another group of white blood cells is collectively referred to as granulocytes or polymorphonuclear leukocytes (PMNs). Granulocytes are composed of three cell types identified as neutrophils, eosinophils and basophils, based on their staining characteristics with certain dyes. These cells are predominantly important in the removal of bacteria and parasites from the body. They engulf these foreign bodies and degrade them using their powerful enzymes.

Macrophages -- Macrophages are important in the regulation of immune responses. They are often referred to as scavengers or antigen-presenting cells (APC) because they pick up and ingest foreign materials and present these antigens to other cells of the immune system such as T cells and B cells. This is one of the important first steps in the initiation of an immune response. Stimulated macrophages exhibit increased levels of phagocytosis and are also secretory.

Dendritic Cells -- Another cell type, addressed only recently, is the dendritic cell. Dendritic cells, which also originate in the bone marrow, function as antigen presenting cells (APC). In fact, the dendritic cells are more efficient apcs than macrophages. These cells are usually found in the structural compartment of the lymphoid organs such as the thymus, lymph nodes and spleen. However, they are also found in the bloodstream and other tissues of the body. It is believed that they capture antigen or bring it to the lymphoid organs where an immune response is initiated. Unfortunately, one reason we know so little about dendritic cells is that they are extremely hard to isolate, which is often a prerequisite for the study of the functional qualities of specific cell types. Of particular issue here is the recent finding that dendritic cells bind high amount of HIV, and may be a reservoir of virus that is transmitted to CD4+ T cells during an activation event.
 

The Immune Response
An immune response to foreign antigen requires the presence of an antigen-presenting cell (APC), (usually either a macrophage or dendritic cell) in combination with a B cell or T cell. When an APC presents an antigen on its cell surface to a B cell, the B cell is signalled to proliferate and produce antibodies that specifically bind to that antigen. If the antibodies bind to antigens on bacteria or parasites it acts as a signal for pmns or macrophages to engulf (phagocytose) and kill them. Another important function of antibodies is to initiate the "complement destruction cascade." When antibodies bind to cells or bacteria, serum proteins called complement bind to the immobilized antibodies and destroy the bacteria by creating holes in them. Antibodies can also signal natural killer cells and macrophages to kill viral or bacterial-infected cells.

If the APC presents the antigen to T cells, the T cells become activated. Activated T cells proliferate and become secretory in the case of CD4+ T cells, or, if they are CD8+ T cells, they become activated to kill target cells that specifically express the antigen presented by the APC. The production of antibodies and the activity of CD8+ killer T cells are highly regulated by the CD4+ helper T cell subset. The CD4+ T cells provide growth factors or signals to these cells that signal them to proliferate and function more efficiently. This multitude of interleukins or cytokines that are produced and secreted by CD4+ T cells are often crucial to ensure the activation of natural killer cells, macrophages, CD8+ T cells, and PMNs is listed in the chart below.

One possible line of therapy is to reintroduce some of these cytokines to people who have severe immune deficiencies. This approach can be tricky because large amounts of any particular cytokine can have serious side effects. Furthermore, their half-life in the body is usually relatively short. Another short-coming of "replacement" therapy is that many cytokines will activate the CD4+ T cells or macrophages harboring HIV, and this could lead to faster rates of HIV production by those cells. Theoretically, this could lead to progression of HIV rather than prophylaxis against opportunistic infections. However, recent progress in this area warrants attention and further study. Lack of interleukin-2 (IL-2) is believed to be one of the major causes of immune deficiency in AIDS. In recent studies where low dose IL-2 was administered to people with HIV, CD4 T cell counts rose, as did anti-viral specific immunity, and natural killer cell cytotoxic activity. Administration of IL-3 to people with HIV is currently under investigation as a treatment for HIV associated cytopenia (low production of cells from the bone marrow). IL-4, a cytokine that activates B cells and also has inhibitory effects on the production of TNF, is currently under investigation for the treatment of Kaposi's sarcoma. GM-CSF (granulocyte macrophage-colony stimulating factor), another growth factor produced by CD4+ T cells, is under investigation for the treatment of decreased white blood cell production for people on ganciclovir therapy.

Additionally, IFN-gamma (gamma interferon) is under investigation as a treatment for people with PCP. Hopefully, these studies will lead to cures for certain opportunistic infections, or for use in inhibiting HIV production and ultimately saving lives.

 
Immunity and the Immune System Term Paper and Term Paper Reference
By Stewart Hare 

Since the 1930’s the western diet has dramatically changed. This change is due to the change in farming from the natural farming process which has developed over 1000’s of years to a modern scientific farming which has changed farming into an industry. This food industry is not interested in producing good quality nutritional food for the nation but food that is easy to store and cheap to produce which in tern will maximise profit. This has changed the western diet to concise of high sugar, fat and protein which is low in vital nutrients.

Not only since the 1930’s has the western diet changed but also people’s lifestyles have changed. The over use of antibiotics, stress at work, lack of exercise, excessive consumption of alcohol, smoking, use of recreational drugs, increases in obesity and low nutritional status of food all affect the immune system and are contributing to the increase in degenerative diseases in western societies.

Since the 1930’s over 3500 man-made chemicals have found their way into modern day food, this does not include hormones, pesticides and antibiotics which are in foods such as meat and grains. These chemicals are not only unnatural but stop nutrients being absorbed and used which hampers the body’s action to heal itself.

In the UK today, 50,000 chemicals are released into the environment by industry and 400 million litres of herbicides and pesticides are used. We in the UK consume 83 billion cigarettes, 80 million painkillers, 26 billion alcoholic drinks and a quarter of a million tons of food chemicals. All of this adds up to a nation whose immune systems are seriously compromised. The immune system is affected for better or for worst by the food that is consumed. Foods such as meat, sugar, salt, saturated fats, alcohol, dairy products and processed foods all have a negative affect on the immune system.

People who consume large amounts of meat are more likely suffer from cancer in later life than those who don’t. Meat is high in saturated fats, hormones, antibiotics, pesticides and herbicides. These all compromise the immune system.

White sugar has around 90% of its minerals and vitamins removed which when consumed makes the metabolism become inefficient, contributing to weight problems, poor energy control and unbalanced blood sugar levels.

Alcohol abuse severely compromises the immune system. Alcoholics suffer from malnutrition due to the reduction of food, impaired metabolism leading to weight loss and suffer from toxicity of the intestines. Alcohol is linked to cancer, hypertension, cerebrovascular disease and coronary heart disease. Regular heavy drinking can lose up to 10 years of your life expectancy by aging the liver, kidneys, heart and brain. Too much alcohol depletes the body of the minerals zinc, calcium, magnesium and also the B vitamins.?

Salt causes high blood pressure, irritates the stomach and retains fluid.

Dairy produces especially milk causes allergies and intolerances both in adults and children. Milk is also a risk factor for diabetes.

Foods that are good for the immune system are foods that are high in antioxidants such as fresh fruit and vegetables especially broccoli, watercress, carrots and peas. Eating plenty of fresh fruit, vegetables and oily fish will boost your immune system. Research has shown that people who consume large amounts of fruit and vegetables have less genetic damage which is one of the precursors to cancer.

Consuming fruit and vegetables such as apples, prunes, citrus fruits, cabbage and lettuce which are high in flavonoids will also boost your immune system. Flavonoids are substances found in plants that can protect your body from disease.

Soy beans are high in isoflavones which are one of the most potent anti-carcinogens of all. Soy products are also good at preventing heart disease.

Oily fish contains Omega 3 oils which keep arteries healthy, reduces the risk of blood clots and lowers cholesterol. Fish high in Omega 3 are salmon, tuna, mackerel and herring.?

Including pre-biotic food such as leeks, Chicory root, Jerusalem artichoke, onions, oats and bananas in your diet will strengthen your gut defence system.

Your lifestyle has a huge bearing on your immune system. Pollution, smoking, work stress, lack of sleep, being overweight, lack of exercise and excessive sunbathing all has a negative effect on your immune system.

Pollutants such as pollen, free radicals, household and industrial chemicals, lead, CFCs, carbon monoxide, cigarette smoke, bacteria, pesticides, chlorine, colourants and aluminium are a fact of every day life. These pollutants and toxins have a negative affect on our bodies. The liver, kidneys, skin and bowel are responsible for removing these pollutants and toxins from our bodies. If these organs are working below par due to a suppressed immune system then toxins will remain in our bodies. This will cause allergies and sensitivities and weakening the immune system further.

Stress, repressed anger, depression and chronic worries depress our immune system by reducing the ability of immune cells to form antibodies. It is a well known fact that when we are stressed we are more likely to get ill. Stress increases blood sugar and lipids which contributes to heart disease, infections and cancer.

Being overweight due to lack of exercise and excessive eating can increase the risk of hypertension and diabetes by 10%. Sun bathing uses up anti-oxidants and can age the skin up to 10 years. Too much exposure to the sun can cause skin cancer. Smoking cigarettes uses up large amounts of vitamin C and other anti-oxidants, this can leave smokers vulnerable to cancer and heart disease. Smoking ages the lungs, skin, circulation, heart and can lead to early menopause and osteoporosis.?

Since the 1930’s both diet and lifestyle has changed. Although there is an abundance of food, it tends to be substandard in nutritional value. The lack of nutrition in our food with the addition of stresses of modern day lifestyles is suppressing our immune systems at a time when we need it most. This combination has lead to a rise in degenerative diseases despite western societies spending billions in health care.

 

Stewart Hare C.H.Ed Dip NutTh

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