Immune system hypersensitivity, or the over-reaction of the immune system, is classified into four primary types. The categories are known as type I, II, III, and IV hypersensitivities.
Type I hypersensitivity, for example, corresponds to allergies. Allergies generate an immediate immune response from the body that can range from uncomfortable to fatal. The mechanisms associated with the allergic response underlie conditions such as atopy, anaphylaxis, and asthma among others.
Anaphylaxis is a severe allergic reaction that affects nearly 1.6% of the general population. The most common sources of anaphylaxis are insect bites and stings, certain foods, and medications. Symptoms may first present like a typical allergic response such as a runny nose or skin rash, but after 30 minutes or so more serious symptoms appear including coughing, dizziness, hives, low blood pressure, shortness of breath, etc. Some people report feeling a "sense of doom" before the attack.
The immune system response originates when parts of the antigen’s molecules are delivered to T-helper cells located in the lymph nodes. A series of immune system reactions then reclassify the antigen as an allergen, a vastly more dangerous threat. After the initial exposure, the body retains allergen-specific antibodies that are prepared to spring into action upon the next exposure.
Anaphylactic shock occurs when blood pressure drops due to blood vessel dilatation and airways constrict. The combination can potentially deprive oxygen to major organs.
Epinephrine is the only sure fire way to immediately stop anaphylaxis. It counteracts the reaction produced by histamines by relaxing airways and constricting certain blood vessels. It is important to administer epinephrine as soon as possible with an auto-inject device such as an EpiPen. When in doubt it is better to be safe than sorry.
The body can gradually be desensitized to certain allergens with immunotherapy. However, desensitization is a very mediated process that is conducted over months or years, and always under trained supervision.
More about immune system hypersensitivities and anaphylaxis:
Med School Phys Podcast:
Hypersensitivity Responses
Mental Floss:
Here’s What Happens to Your Body During Anaphylaxis
