Type III Hypersensitivity: Immune Complex Hypersensitivity

Type III Hypersensitivity: Immune Complex Hypersensitivity
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  • 0:05 Internal Voice
  • 0:33 Type III…
  • 2:51 Vasculitis, Arthritis,…
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Lesson Transcript
Instructor: Artem Cheprasov
This lesson will discuss what a type III hypersensitivity reaction causes. It will delve into which antibodies are involved, the creation of immune complexes, the development of arthritis, vasculitis, and glomerulonephritis, and much more.

Internal Violence

We've all heard of the unfortunate cases where gang violence leads to innocent bystanders getting hurt. Unfortunately, gang violence isn't just part of the world around us; it's also part of the world inside us. Our immune system engages in plenty of gang violence, so to speak, that ends up hurting our own body's cells, the innocent bystanders, in the process.

Type III Hypersensitivity Reactions

The gang violence I described is called type III hypersensitivity, or immune complex hypersensitivity. Why it's called that will be made clear in just a second.

In our immune system, we have little gangsters called antibodies. They fight for their turf - for their ground, so to speak. Their ground is our body. They want to defend our body because they need it for survival. Well, whenever an invader enters our body, such as a virus, bacteria, and so on, our antibodies, namely IgG and IgM in type III hypersensitivity, love to gang up on these guys - to neutralize them, get rid of them, and prevent them from hurting our body.

Each antibody will grab hold of a recognizable particle of an invader, called an antigen. Another antibody will grab hold of that same particle with one arm and another particle with the other arm. Further still, other antibodies will continue this chain reaction until immune complexes are formed. These immune complexes are aggregates of antibodies and antigens. They are supposed to serve a good purpose. When you have more antibodies than antigens, very large clumps of antibody-antigen complexes can be formed. These large clumps are easily recognized and engulfed by white blood cells, called phagocytes, for destruction.

However, when there are slightly more antigens than antibodies for that specific antigen, your body can only form smaller-sized aggregates of antibodies and antigens. There just aren't enough antibodies to go around and form a chain reaction large enough to form large immune complexes. This is bad, because smaller immune complexes aren't as readily or easily cleared by phagocytes. Instead, these smaller immune complexes float around freely and get lodged in all sorts of different tissues, such as kidney glomeruli, joint capsules, and blood vessel walls.

Vasculitis, Arthritis, and Glomerulonephritis

This is the point at which our gang violence causes trouble to the community (our body, so to speak). When these smaller immune complexes lodge in these places, they cause innocent bystanders - the kidneys, blood vessels, and joints, among others - to get hurt. After getting stuck in one of the places I just mentioned, these immune complexes activate little proteins called complements, which in turn activate white blood cells that cause an inflammatory response. These cells include, among others, mast cells, macrophages, and neutrophils. The molecules released by the cells cause local inflammation, which attracts more inflammatory cells, which release more inflammatory mediators.

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