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Antibodies: Their Function In the Immune System

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  • 0:07 Antibody Function
  • 0:35 Osonization
  • 2:53 Agglutination
  • 4:12 Neutralization
  • 5:27 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov
This lesson will delve into the three main ways by which antibodies function. We're going to discuss opsonization, agglutination and neutralization. We'll also learn what the Fc region is and why it's important.

Antibody Function

Antibodies, or immunoglobulins, are little glycoproteins floating around in your body that help you fight off a lot of terrible disease-causing bacteria, viruses and the like. You know that much, I'm sure. However, this lesson will go into a few more specifics on the various methods antibodies actually use to rev up your immune system and therefore protect you.

Opsonization

When our Y-shaped antibodies are released by antibody-producing factories called plasma cells, they float off to attach to a very specific antigen, like a protein on the surface of a foreign cell.

Let's use a bacterium in our example. Antibodies will be made for a specific molecule on the bacterium's surface. Only the variable domain, which is at the tip of both arms of the Y-shaped antibody, will be able to bind to a very specific molecule on the bacterium.

Once one or both of the arms of the Y-shaped antibody have bound to the antigen on the bacterium, the tail portion of the Y-shaped antibody, known as the Fc region, will stick out into space for several important reasons.

The Fc region will help to initiate a sequence of events involving other protein molecules, called complements. There are two main outcomes in the interaction between antibodies and complements. One will result in the lysis, or bursting open, of the cell the antibodies are attached to. You can basically imagine that the arms of the antibodies have sharp needles. As they come into contact with the fluid-filled balloon, our bacterium, a hole is created in the surface, causing the cell or balloon to burst apart. This obviously means the cell will die.

The other outcome is that the interaction between antibodies and complements will cause a process whereby a foreign substance coated by antibodies and complements is rendered more likely to be phagocytized. This process is called opsonization. Basically, opsonization is a mixture of proteins that acts like a juicy sauce on a meal. This juicy sauce, spread all over the cell, attracts phagocytes, which are white blood cells that ingest and kill foreign invaders in a process called phagocytosis.

Agglutination

While the antibodies can act as a juicy sauce to help attract dinner mates to kill the bacterium - or any other invader for that matter - antibodies can also act like sticky syrup. Since each Y-shaped antibody has two places it can bind something, it can use both arms to good effect. One arm can grab hold of one cell, and the other arm can grab hold of another identical cell. This makes the cells stick to one another. More antibodies can join in and form a chain reaction where lots of foreign invaders are stuck together and cannot move. It's like those sticky fly traps! The flies, or deadly pathogens, aren't going anywhere!

Once all of those cells are trapped, the tail, or Fc region of the antibodies, sticks out of the sticky clumps. Cells such as macrophages will recognize these regions and engulf the sticky mess for destruction. Other cells will recognize the Fc region and release substances that will kill the foreign cells on the spot.

This process, the process whereby antibodies cause cells to clump together, is called agglutination. I hope you can hear the 'glue' in agglutination.

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