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Student Guide: What are the Odds? Modeling the Chances of Getting an Autoimmune Disease

Downloadable and printable Student Guide PDF.
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Summary

Autoimmune diseases are pretty common, with more than 23.5 million people in the United States (or about 1 in 13) having one. Autoimmune diseases happen when a person's immune system attacks the person's own body by accident. Find out how this can happen by making a model with M&M's® candies and a six-sided die.

Useful Vocabulary

  • Immune system: Organs and cells in a person's body that normally defend against germs and harmful microorganisms.
  • Pathogen: A microorganism (or tiny, microscopic organism) that can make a person sick. Pathogens include harmful bacteria, microscopic fungi, viruses, and more.
  • Immune response: A series of steps the immune system goes through to fight off a pathogen. The immune system needs to recognize the pathogen and then attack and destroy the pathogen.
  • White blood cells: Also called leukocytes, these cells do most of the work in the immune response. There are several different types of white blood cells, each with a slightly different job, including B cells and T cells.
  • Antibodies: Tiny particles made by white blood cells that can attach to, or bind, a pathogen. The pathogen can then be destroyed by white blood cells.
  • Autoimmune response: Also known as autoimmunity, this is when the immune system accidentally makes an antibody that binds to its own healthy cells. It is common and usually not a problem, but if the body does not recognize the mistake, it can turn into an autoimmune disease.
  • Autoimmune disease: When the immune system attacks healthy cells in the body. A person's genetics can make them predisposed, meaning they have a higher risk of getting an autoimmune disease. Other factors (such as where a person lives, what they eat, and what things they are exposed to) can also affect whether they get an autoimmune disease.
  • Autoimmune response checkpoints: The immune system has checkpoints to stop an autoimmune response from turning into an autoimmune disease. If a checkpoint fails, it can cause an autoimmune disease. There are three checkpoints that you will explore in this activity:
    1. Checkpoint 1: Sometimes white blood cells (specifically B cells, which are made in the bone marrow, or T cells, which are made in the thymus) are made that have autoimmunity, meaning their antibodies bind human cells. The body must destroy them before they escape from the bone marrow or thymus, or they can cause an autoimmune disease.
    2. Checkpoint 2: Right before an immune response is triggered to fight a pathogen, white blood cells (called regulatory T cells) make sure that other white blood cells are not accidentally attacking the body's own cells. They need to do their job correctly to prevent an autoimmune disease.
    3. Checkpoint 3: After a pathogen is destroyed in the body, white blood cells (specifically activated T cells and B cells) must destroy themselves (through a process called apoptosis) to stop the immune response, or it could lead to an autoimmune disease.

Materials

To do this activity, you will need:

  • Bowl or cup of M&M's candies with an equal number of each color (1)
  • Six-sided die (1)
  • Pencil or pen (1)

Directions

  1. In this activity, you will be modeling the immune system to see how autoimmune diseases can develop. To investigate this, your model will use the three different autoimmune response checkpoints discussed. When testing your model, you will fill out two data tables. The first data table represents a group of 20 people with a normal chance of developing an autoimmune disease. The second data table represents a group of 20 people whose genetic makeup makes it more likely for things to go wrong at autoimmune checkpoints 2 and 3 (described in the Useful Vocabulary section). How common do you think autoimmune responses are for each group? How often do you think those responses will turn into a full-blown autoimmune disease for each group?
Normal Chances of Autoimmunity Group
Step in the ModelPerson Number
  12345678910 11 12 13 14151617181920
Setup What color was picked?                        
Checkpoint 1 Color match? (Yes/No)                        
If yes, what was the die number? (1 to 6)                        
Checkpoint 2 Color match? (Yes/No)                        
If yes, what was the die number? (1 to 6)                        
Checkpoint 3 Color match? (Yes/No)                        
If yes, what was the die number? (1 to 6)                        
Did the person get an autoimmune disease? (Yes/No)                        
Table 1. This data table represents a group of 20 people who have a normally functioning immune system. As with every individual, each one still has some risk of developing an autoimmune disease. Fill this data table out first. Download Table 1 (pdf).
  1. To fill out the data table, follow the directions in the "Autoimmunity Model" flowchart, below. Go through the flowchart for each of the 20 people in the data table. Use these steps to help guide you through the process:
    1. Whenever you randomly pick a candy, look away from the bowl and mix the candies a little so you do not know which color you will pick. No peeking!
    2. In the "Setup" row, write the color of the candy you picked in your data table for each person.
    3. Write your results in the data table as you test the model.
    4. If you do not have to roll a die when testing checkpoints, skip the "If yes, what was the die number?" row for that person.
    5. If you pick matching colors and roll a die, testing should end for this person only if a 6 is rolled on the die. This means the person got an autoimmune disease.
    6. Be sure to read the blue "What it represents" boxes in the flowchart so you know what you are modeling.
    7. At the beginning of the "Setup" and each checkpoint, make sure all candy has been returned to the bowl and there is still an equal number of each color.
Flowchart for testing the autoimmunity model
Figure 1. This is a flowchart of the model you will use in this activity. The "What it represents" blue boxes explain what each part of the model represents. As you follow the steps in the model and fill out each data table, keep the information in the boxes in mind.
  1. Were there many times when a person had an autoimmune response that did not turn into an autoimmune disease (i.e., the M&M's colors matched but the die roll was not a 6)? Did any of the people end up getting an autoimmune disease?
  2. Now look at the "Higher Risk at Checkpoints 2 and 3 Group" data table.
Higher Risk at Checkpoints 2 and 3 Group
Step in the ModelPerson Number
  12345678910 11 12 13 14151617181920
Setup What color was picked?                        
Checkpoint 1 Color match? (Yes/No)                        
If yes, what was the die number? (1 to 6)                        
Checkpoint 2 Color match? (Yes/No)                        
If yes, what was the die number? (1 to 6)                        
Checkpoint 3 Color match? (Yes/No)                        
If yes, what was the die number? (1 to 6)                        
Did the person get an autoimmune disease? (Yes/No)                        
Table 2. This data table represents a group of 20 people who are at higher risk for developing an autoimmune disease at checkpoints 2 and 3. Download Table 2 (pdf).
  1. Repeat the modeling process to fill out the new data table, but this time if you have a color match and roll a die, do the following:
    1. If the color match occurs when you are at checkpoint 1, then testing should end for the person only if a 6 is rolled on the die, again meaning the person got an autoimmune disease.
    2. If the color match occurs when you are at checkpoint 2 or 3 (meaning the person is at higher risk), then testing should end for this person if a 2, 3, 4, 5, or 6 is rolled on the die (but not if a 1 is rolled). This means the person got an autoimmune disease.
  2. In the "Higher Risk at Checkpoints 2 and 3" data table, how many times did a person have an autoimmune response but not develop an autoimmune disease? Did any of the people end up getting an autoimmune disease?
  3. Calculate the percentage of people who got an autoimmune disease for each data table. To do this, count up the number of times you wrote "Yes" in the bottom row, then divide that number by 20. For example, if in one of your data tables 3 people got an autoimmune disease, the percentage would be 3 divided by 20, which is 0.15 or 15%.
  4. Compare your results from each data table. Were there people with higher risk at none of the checkpoints that got an autoimmune disease, or people with two checkpoints at higher risk that did not get an autoimmune disease? Were there many times when a person had an autoimmune response that did not turn into an autoimmune disease? Overall, what do your results tell you about being genetically predisposed to getting an autoimmune disease and the likelihood of actually getting one?

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