Body: Exploring Immunity and Allergy

The Immune System
The immune system is the mechanism within the body that enables it to protect itself against harmful substances likely to trigger illness or disease. It is in effect the body’s first line of defence. Not only does the immune system protect the body from the infiltration of micro-organisms and other materials that are detrimental to the body,it also provides protection against cancer by destroying defective cells.

The work of the immune system is not always benign however. It can sometimes lead to overreactions which can trigger allergic responses leading to conditions such as eczema, hay fever and asthma. A weakened immune system can make the body more susceptible to infection. At its worst, a compromised immune system can lead to auto immune conditions such as systemic lupus erythematosus (SLE) that are activated when the body treats it own cells as if they were harmful and the immune system begins to attack them.

Work of the Immune System
The helpful versus harmful nature of the immune system is determined by type of immunity- whether it is active or passive. In addition the immune system itself can either be over active or under active as follows:
Constituent Parts of the Immune System
The important components of the immune system include cells, chemicals and tissues. Cells- the most important cells within the immune system are T cells, B cells, antigen-presenting cells (APCs), neutrophils and mast cells. T cells are a type of white cell (lymphocyte). They are found in the blood, bone marrow and lymph nodes. They stimulate another group of white cells known as B cells in order to produce antibodies. They can also directly destroy antigens such as viruses that invade the body’s cells. B Cells as referred to above are also found in blood, bone marrow and lymph nodes. When stimulated by the T cells they turn into plasma cells and secrete antibodies. Antigen-presenting cells (APCs) are found in the skin and throughout lymph tissues. They process antigens so that they can be identifies and dealt with by the T cells. Another type of APC are macrophages which are responsible for disposing of foreign matter and debris resulting from the immune processes. Neutrophils are the commonest form of white blood cell, they also have a similar function to macophages. Mast cells are found throughout the body and release chemicals such as histamine that trigger inflammation in response to an immune reaction. Chemicals- antibodies are also known as immunoglobulins such as IgG, IgM, IgA, IgE and IgD are proteins secreted by plasma cells that activate enzymes triggering the destruction of bacteria and other pathogens by blood and tissue cells. Tissues- although many immune reactions occur in the bloodstream, lymph tissue is also important to immunity, for example lymph nodes (found throughout the body in such as neck, armpits and groin).

Triggers for immunity
Immune reactions are caused by the release of histamine and other chemicals from mast cells in the immune system which result in inflammation, swelling and contraction of smooth muscle. This response is an immediate response to foreign organisms and chemicals and can lead to asthma, eczema, hay fever, food allergies. Severe reactions can cause nausea, wheezing, itching, low blood pressure, abdominal pain, nettle rash and in sever cases, loss of consciousness. Examples of Conditions affecting the Immune System
The following conditions develop in response to immune system activity:
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