Type I Hypersensitivity: Allergic Reactions

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  • 0:05 Hypersensitivity Reactions
  • 0:47 Type I Hypersensitivity
  • 1:41 The Pathophysiology of…
  • 3:28 Anaphylactic Shock
  • 4:11 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson delves into something known as type I hypersensitivity reactions. You'll find out how everything from mast cells, basophils, and IgE to histamine, bee stings, and peanut allergies all play a role in this process.

Hypersensitivity Reactions

Your immune system is definitely there for a good reason. It helps protect you against some nasty things. However, every now and then something goes wrong. It's not a perfect system by any means. If it were, it would be infallible, and we would have no reason for this lesson. However, sometimes our immune system produces excessive and even fatal reactions to everything from allergens to pathogens to even our own body's cells or receptors. These types of reactions are called 'hypersensitivity reactions,' and we'll be focusing in on one major type in this lesson.

Type I Hypersensitivity

The first type of hypersensitivity reaction is called, unsurprisingly, type I hypersensitivity. This is appropriately called 'immediate hypersensitivity' because your body's response to an antigen occurs immediately, or within minutes of exposure to it. This is the most common type of hypersensitivity reaction, and therefore, I'm more than sure you can come up with several examples of substances or events that can cause you a combination of:

  • Redness
  • Swelling or congestion
  • Pain
  • Itching

For example, some things that can cause these signs include:

  • Bee stings
  • Drug allergies to things like penicillin
  • Food allergies to things like peanuts or milk
  • Pollen, which may cause allergic asthma
  • Atopy, or a genetic predisposition to allergies

The Pathophysiology of Type I Hypersensitivity

In essence, if it causes a fast onset allergic reaction to something your body encounters, it's a type I hypersensitivity reaction.

The way all of the things I mentioned above work is mainly thanks to an antibody called IgE, which is the primary class of antibody involved in type I hypersensitivity reactions.

Once your body is exposed to an allergen, it makes IgE antibodies specific for that allergen. However, in people hypersensitive to an allergen, the level of IgE specific to the allergen is sometimes thousands of times higher than in people not allergic to the same compound.

These antibodies then use their Fc, or tail portion, to attach to the surface of white blood cells, called mast cells and basophils, which are the primary cells involved in type I hypersensitivity reactions.

Only when you are re-exposed to the same allergen does the allergen actually cause you issues, as it binds to the arms of the Y-shaped antibody IgE located on the surface of the mast cells and basophils.

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