Immune Deficiency Diseases: Definitions & Types

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  • 0:28 What is the Immune System?
  • 1:12 Immune Deficiency
  • 2:15 HIV & AIDS
  • 3:02 SCID & CVID
  • 5:07 Graft-vs-Host Disease
  • 6:33 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson will teach you about the immune system, what immune deficiency means, why that's dangerous, and about the important causes of such a problem, including HIV/AIDS, SCID, CVID, and more.

Immune System Diseases

For this lesson, let's pretend we are part of a local town's police force. You can be the sheriff if you want. You're located in a building, you're in charge of training the new officers on staff, and they're in charge of patrolling the city streets to ensure the safety of the neighborhood using their cars, radar guns, badges, and, of course, actual guns. We'll use this storyline to discuss important diseases that involve immune system deficiency.

What Is the Immune System?

The immune system is a collection of cells, tissues, and organs that are responsible for fighting off infection and disease. It helps us protect our body from viruses, bacteria, fungi, and parasitic worms, all trying to use our body's precious resources or destroy us outright. By that definition I think it's clear the connection between the immune system and your police force.

Your police force patrols the neighborhood and your immune system's cells patrol your body. You have buildings where officers come in to work, where they train, and where they hold criminals. The body also has tissues and organs where immune system cells are trained, where they haul off suspects to, and where the officers sit and work.

Immune Deficiency

But unfortunately, your police force, like some in real life, is a bit under budget. There's not all that much money to hire or train officers, to heal injured policemen and women, and to keep the buildings in appropriate shape. When your body's immune system is affected in a similar way, it results in an immune deficiency disorder. This is when your body, whether due to genetics or disease, doesn't have enough immune system cells to properly fight off disease or when it has dysfunctional tissues and organs that result in an inadequate production of immune cells.

Anyways, you can appreciate that if your police force is short on staff and has inadequate buildings, cars, and equipment, it cannot do a very good job of preventing crime or stopping criminals in their tracks. This causes an increase in thefts, fires, and an overall high crime rate around your neighborhood. Let's discuss how this scenario can arise in your body, resulting in a predisposition to disease, by discussing some immune deficiency problems.


One very famous example is AIDS, or acquired immunodeficiency syndrome. AIDS is caused by a virus known as HIV, or human immunodeficiency virus. Anyways, this virus is like a crook that enters your body and kills important immune system cells, called CD4+ T cells, the cells that are actually supposed to kill the virus!

This results in a depletion of police officers in the body and because there are fewer police officers at your disposal, they are unable to catch opportunistic pathogens, which are disease causing agents that attack the body when it is weak, meaning these guys are normally too afraid of the police, but when they see there are fewer of them, that's when they strike the body to cause disease.


But these immune deficiency disorders don't always have to strike at the already well-trained officers in your police force. Sometimes they strike at the police academy center, thereby ensuring your cadets never get the training they need, meaning these cadets never fully develop, and the few that do tend to be dysfunctional because of the poor training.

An example of this case is something abbreviated as SCID, or severe combined immunodeficiency. This disorder arises due to a genetic mutation, meaning your genes, the architects and writers that design the training center and manual, are defective. This obviously leads to poorly trained or even non-existent immune system cells in your body.

Namely, it is the white blood cells called B and T cells, or B and T lymphocytes, that are affected. If you've ever heard of the bubble boy, then you know how deadly SCID can be, as severe combined immunodeficiency is sometimes known as the bubble boy disease. The children born with this disorder are so deplete of police officers in their body that they are very susceptible to very dangerous infections that may easily kill the child very quickly if left untreated.

Another way by which your police force can be affected is due to a lack of equipment. I mean, if you had a lot of officers, but they didn't have any weapons to fight criminals, then obviously they'd be of little to use to you. Well, there is a disease abbreviated as CVID, or common variable immunodeficiency, that causes your police force to lose its weapons.

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