People who over react to certain substances to which other people are not hypersensitive are said to be allergic. The substances which cause allergic reactions are called allergens, and common allergens include foods (such as milk, shellfish, eggs), antibiotics (penicillin), venoms (wasps, bees), plants, dust or chemicals.
Types of Allergic Reactions
There are 4 types of allergic reactions:
Type I (anaphylactic) reactions
When a person becomes sensitized to an allergen, the immune system makes an imprint of the allergen so that it can be recognized the next time it enters the body. The immune system does this by producing an antibody (IgE) that matches the allergen and puts it on mast cells and basophils. Once the person becomes re-exposed the allergen will bind to the antibody. Mast cells and basophils release substances such as kinins, leukotrienes, histamine and prostaglandins. These substances cause increased blood capillary permeability, blood vessel dilation, constriction of lung airways and increased mucus secretion. The bodies immune system may induce a full anti-inflammatory response. The problem is that there is no need for such a reaction. The immune system sees a threat in specks of dust, or pollen that would otherwise never really harm a person.
The reaction can become life threatening with the onset of anaphylactic shock. The airways constrict even further, and the person goes into shock as there is fluid is lost from blood. Norepinephrine is usually used to treat this as it dilates the airways and causes a stronger heartbeat.
Type II (cytotoxic) reactions
This type of reaction occurs when antibodies (IgG and IgM) over-react to antigens on blood cells. The complement system is normally activated, releasing proteins in an attempt to destroy the potential danger. This reaction commonly occurs in the event of a mismatched blood transfusion.
Type III (immune-complex) reactions
This reaction occurs when some antigens escape from being destroyed by the immune system. The escaped antigens become logged under parts of blood vessels. Here they activate the complement system and cause inflammation. This process is the basis of autoimmune diseases such as rheumatoid arthritis.
Type IV ( cell-mediated) reactions
Normally referred to delayed hypersensitivity as this type of reaction begins after 12 – 17 hours after being exposed to the allergen. Some of the allergen is taken up and chopped into pieces and displayed on antigen presenting cells. These cells then migrate to the lymph nodes where they present the antigen to T cells. The cells play a role in coordinating an inflammatory response. Bacteria such as myobacterium tuberculosis, and toxins such as poison ivy can illicit this type of reaction. The reaction is also the basis of the tuberculosis skin test.
Allergy Treatments
There is a large number of medications available to treat allergies. Treatments are different because of the vast allergens available, the different ways to which our bodies react and the many kinds of antibodies involved.
Antihistamines are some of the most commonly used allergy medications used today. They can be used in reactions such as Type I reactions where histamine is released. Histamine mainly causes sneezing, increased mucus production or itching. Antihistamines bind to the same receptor that histamine binds to. This prevents histamine from stimulating cells and causing adverse reactions.
Related Posts
Commonly known as “hay fever,” seasonal allergies are inflammations of the mucous membranes which line the nasal passages and are caused by a particularly sensitive or over-reactive...
Coughing is the body’s natural reaction to remove substances from the throat and lungs. There are several types of coughs Productive cough are wet and produce sputum or mucus...
Schizophrenia is a psychiatric term for an assortment of grave and chronic mental disorders of the brain which result in distortions or misinterpretations of reality. The name...
A rash is a skin disorder that may appear over a small area of the body or it may be widely spread over various large areas or even over the entire skin of the body. Wherever...
The brain disorder, schizophrenia affects over 2 million adults in America usually before the age of 30.
What is Schizophrenia?
Schizophrenia is a disorder of the brain that...
Comments
Recent Comments