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Fighting the Flu: How Your Immune System Uses Its Memory

Difficulty
Time Required Short (2-5 days)
Prerequisites None
Material Availability Iron filings may need to be specially ordered. See the Materials and Equipment list for details.
Cost Low ($20 - $50)
Safety No issues

Abstract

Being sick is no fun, especially when your friends are doing exciting activities that you have to miss out on. Thankfully, common illnesses usually last for just a few days, and then you start to feel better. Why is this? It is thanks to the immune system, which is a group of special organs and cells in your body that constantly work to keep you healthy. In this science project, you will make a simple model to investigate how the immune system defends the human body from common illnesses, and the role of the immune system's memory in this process.

Objective

Investigate how memory cells in the immune system help the human body fight off illness.

Credits

Teisha Rowland, Ph.D., Science Buddies

Cite This Page

MLA Style

Science Buddies Staff. "Fighting the Flu: How Your Immune System Uses Its Memory" Science Buddies. Science Buddies, 30 June 2014. Web. 20 Aug. 2014 <http://www.sciencebuddies.org/science-fair-projects/project_ideas/HumBio_p036.shtml>

APA Style

Science Buddies Staff. (2014, June 30). Fighting the Flu: How Your Immune System Uses Its Memory. Retrieved August 20, 2014 from http://www.sciencebuddies.org/science-fair-projects/project_ideas/HumBio_p036.shtml

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Last edit date: 2014-06-30

Introduction

Have you ever been sick for a few days, but soon felt better? If so, you can thank your immune system! Your immune system is made up of different cells and organs in your body and normally defends you against germs and harmful microorganisms (pronounced my-crow-or-guh-nih-zums) all the time, whether you notice it or not. It does this so that you do not get sick, or so you get well quickly if you do get sick.

You are constantly being exposed to microorganisms, which are microscopic organisms. This means they are so small that you usually need a microscope to see one of them. Some microorganisms are more dangerous than others. In fact, our bodies actually need some types of microorganisms for us to live, such as certain bacteria in our stomachs that help us digest food. Any microorganism that can make you sick is called a pathogen. Pathogens include harmful bacteria, microscopic fungi, and viruses. If a pathogen gets into a person's body and makes him or her sick, then the person is said to be infected by that pathogen, or have an infection. For example, if a person gets infected by a virus, it is called a viral infection. Some viral infections can cause the flu. As another example, some bacterial infections can cause strep throat. Your immune system constantly tries to defend you against all of these pathogens so that you do not get an infection.

How does your immune system protect you from pathogens and keep you healthy? The immune system goes through a series of steps called the immune response to fight off any pathogens. Basically, the immune system must first recognize the pathogen and then attack and destroy it. You can watch this video from KidsHealth to see the immune response in action. Note: The video goes into more detail than will be covered here.

Video of immune response
This video gives a detailed introduction to the immune response.
Watch this Kidshealth video introduction to the immune response: http://kidshealth.org/kid/htbw/ISmovie.html

Most of the immune response work is carried out by white blood cells, also called leukocytes (pronounced loo-ko-sites). There are several different types of white bloods cells, each with a specific job; you can think of them as soldiers, each with a special skill, that collectively work to defend your body against an invading pathogen. If you are interested in learning about the specific job of each type of white blood cell, read the resources in the Bibliography. For this science project, it is enough to know that the job of some types of white blood cells is to find pathogens. When they are looking for pathogens, it is very important that these cells can tell the difference between the body's own cells (normal cells) and the pathogens (cells that are not the body's own). This is referred to as self/non-self recognition. If a person's body stops being able to tell the difference between self and non-self then the body starts attacking itself as if it were a pathogen, which often results in an autoimmune disease.

In a normally functioning immune system, once a pathogen is found, a subset of white blood cells (called B-cells) make antibodies to the pathogen. An antibody is a tiny particle that is much smaller than even a cell or most pathogens, that both tags a pathogen as "non-self" and helps to destroy the pathogen. A diagram of antibodies binding onto a pathogen is shown in Figure 1 below. Notice that multiple copies of an antibody will often grab onto a single pathogen. It is also important to know that antibodies are usually unique, meaning that flu antibodies can not grab onto a strep throat caused by bacteria, nor can antibodies to the bacteria identify and destroy a flu virus.

Human Biology science project Drawing of antibodies binding a bacterium.
Figure 1. During the immune response, antibodies (shown in blue) bind to a pathogen (a bacterium here, shown in red). Once bound to the pathogen, the antibodies often then get help from white blood cells to destroy the pathogen. Note: These are simplified drawings that are not to scale.

Here is where it really gets interesting! Once the pathogen is defeated, some white blood cells leave a memory cell behind. Memory cells remember specific pathogens they have "met" before. Because of this, they can make a larger and faster immune response if they meet the same pathogen again. This means that more antibodies will be around to fight the same pathogen when it gets into the body again. One example you might be familiar with is the importance of being vaccinated against certain diseases. Vaccines usually work by exposing your body to a harmless version of a normally dangerous pathogen, such as tetanus or the flu. Then, if you ever encounter the real pathogen, your body can fight it off.

In this medical biotechnology science project, you will make a model of the immune system in the human body and investigate how memory cells help the body fight off an infection. A model is something that engineers and scientists build to represent an object or process in nature, to make it easier to study. It is usually a simplified version of that object or process. For example, sometimes engineers build small models of bridges that are easy to hold and examine, so they can study it before they build the real bridge. In your immune system model, the antibodies will be represented by magnets, pathogens will be represented by iron filings, and cells of the human body will be represented by salt. If a pathogen has memory cells that were made for it, then the immune system should remember it and make more antibodies to fight off the pathogen. How does having more antibodies help the immune system fight off pathogens? Get ready to find out!

Terms and Concepts

  • Immune system
  • Microorganism
  • Bacteria
  • Pathogen
  • Infection
  • Immune response
  • White blood cell
  • Self/non-self recognition
  • Autoimmunity (or autoimmune response)
  • Autoimmune disease
  • Antibody
  • Memory cell
  • Vaccine
  • Model

Questions

  • What are some examples of common pathogens?
  • In the immune response, what do antibodies do?
  • What do memory cells do?
  • What can cause an autoimmune disease?

Bibliography

For help creating graphs, try this website:

Materials and Equipment

  • Glass jar with lid, 16 oz. A smaller or larger glass jar (with lid) would work too, but the amount of iron filings and salt will need to be adjusted accordingly.
  • Salt (1 cup)
  • Measuring cup
  • Measuring tablespoon
  • Iron filings (1 tbsp.). Iron filings are available from educational material suppliers or online at Amazon.com.
  • Magnetic tape (1 inch wide, at least 3 inches long). It can be adhesive-backed or not. Magnetic tape is available from craft stores or online at Amazon.com.
  • Ruler
  • Scissors
  • Plastic wrap
  • Twist ties (3)
  • Piece of paper
  • Digital scale with 0.1-g increments. A digital scale that would be suitable (the Fast Weigh MS-500-BLK Digital Pocket Scale) is available from Amazon.com.
  • Optional: Small tray, lightweight disposable bowl, or another piece of paper
  • Optional: Camera
  • Calculator
  • Lab notebook

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Experimental Procedure

Preparing the Immune System Model

In this part of the science project, you will prepare your model of the human body's immune system. You will fill a jar with salt (representing human cells) and iron filings (representing pathogens). The completed jar will serve as a model of an infected human body. Small magnet pieces will represent human antibodies. Note: Each magnet piece will represent many antibodies. The model antibodies should bind to the model pathogens because iron filings are magnetic.

  1. Note: For convenience, this science project involves household measuring tools, so volumes are given in terms of United States customary units (such as cups and tablespoons). However, science is done in metric units, so you may need to convert when writing up your procedure. To convert units, you can use this metric conversions & US customary unit conversion calculator.
  2. Carefully fill the glass jar with 1 cup (c.) of salt so that the jar is about half full.
  3. Add 1 tablespoon (tbsp.) of iron filings to the salt in the jar. It should now look similar to the jar shown in Figure 2 below.
    1. Be sure to clean the measuring tablespoon with water and soap after the iron filings have been in it before using it with food.
Human Biology science project Image of iron filings and salt in a glass jar.
Figure 2. Fill the jar with 1 c. of salt and then 1 tbsp. of iron filings.
  1. Put the lid tightly on the jar.
  2. Mix the salt and iron filings together by flipping the jar upside down and then right-side up again. (This is called inverting the jar.) Do this about 10 times (taking about 1 second [s] each time you invert the jar), or until the iron filings appear to be evenly dispersed throughout the salt in the jar, as shown in Figure 3 below.
    1. How easy is it to see the iron filings in the jar? Does it seem like there is a lot more salt compared to the amount of iron filings? Write any observations you make in your lab notebook.
    2. The jar of salt and iron filings is now ready to act as a model of an infected human body. Set the jar aside for now.
Human Biology science project  Image of salt and iron filings mixed together in a jar.
Figure 3. Put a lid on the jar and invert it about 10 times, or until the iron filings are evenly dispersed throughout the salt. You should now just see some speckling of iron filings throughout the salt in the jar.
  1. Carefully use scissors to cut the magnetic tape so that you have three squares of tape. Use the ruler to make each square 1 inch by 1 inch, as shown in Figure 4 below.
    1. Tip: Since the tape should be 1 inch wide, you should only need to cut the tape every 1 inch.
    2. If the tape is adhesive-backed, leave the paper strip on the tape so that the adhesive is covered.
Human Biology science project  Picture of three magnet tape squares.
Figure 4. Cut the magnetic tape into three squares that are each 1 inch by 1 inch. This picture shows the sides of the magnets where the paper covers their adhesive backs. (If the magnets are adhesive-backed, leave this paper on.)
  1. Carefully cut the plastic wrap so that you have three squares that are about 4 inches by 4 inches.
    1. You can use the cutting edge on the plastic wrap container or you can use scissors to do this.
  2. Put a magnetic tape square in the middle of a plastic wrap square, as shown in Figure 5 below.
    1. If the magnet is adhesive-backed, place the magnet so that the adhesive side (still covered by the paper) is facing up.
Human Biology science project Picture of a magnet tape square on a piece of plastic wrap.
Figure 5. Place a magnetic tape square onto the middle of a plastic wrap square.
  1. Pull the ends of the plastic wrap together, around the magnetic tape square, and then twist the plastic wrap ends together. With the plastic wrap ends twisted, take a twist tie and tie it around the ends, holding them securely together, as shown in Figure 6 below.
    1. Make sure there are no openings in the plastic wrap where salt or iron filings could get through and reach the magnetic tape.
Human Biology science project Picture of a magnet tape square wrapped in plastic wrap.
Figure 6. Twist the plastic wrap around the magnetic tape square and secure the plastic wrap with a twist tie.
  1. Repeat steps 8 and 9 two more times with the other plastic wrap and magnetic tape squares you made in steps 6 and 7.
    1. You should now have three antibody models that look like Figure 7 below. Note: Although each one will be referred to as a single antibody, in your model it actually represents many antibodies.
Human Biology science project Picture of three magnet tape squares each wrapped in plastic wrap.
Figure 7. Prepare two more antibodies as you did the first one so that you have a total of three.

Testing Your Model

In this part of the science project, you will investigate how your model of the human immune system works (remember, the jar of salt and iron filings represents an infected human body, and the magnet tape squares wrapped in plastic wrap represent antibodies). Specifically, you will investigate how the memory cells help the immune system fight off an infection. If a pathogen has memory cells that remember it, then the immune system should be making more antibodies to fight off the pathogen. As a result, you will use your model to test how having more antibodies helps the immune system fight off pathogens.

  1. In your lab notebook, create a data table like Table 1 below. You will record your results in this data table.
  Three Antibodies Together
  One Antibody Alone 1st Antibody2nd Antibody3rd AntibodyTotalAverage
Trial 1: Weight (g)       
Trial 2: Weight (g)       
Trial 3: Weight (g)       
Table 1. In your lab notebook, create a data table like this one to record your results in. You will be recording the weight (in grams [g]) of what the antibodies remove from the infected human body model.
  1. Take a piece of paper and fold it in half width-wise, making a crease. Then fold it in half width-wise and crease it again. Unfold the paper. It should look similar to the one in Figure 8 below. Set this paper aside for now; you will be using it in step 7 below. Note: You are folding the paper to help keep the salt and iron filings on the paper when they are released from the magnet tape. (The creases should help you keep the salt and iron filings closer to the middle of the paper.)
Human Biology science project Picture of a folded piece of paper.
Figure 8. Fold the piece of paper in half twice and then unfold it. It should look similar to this one. Folding the paper this way should help keep the salt and iron filings on the paper.
  1. Take one of the antibody models and place it in the jar of salt and iron filings, as shown in Figure 9 below.
Human Biology science project Picture of a magnetic tape square ('antibody') in a jar of salt and iron filings.
Figure 9. Gently place an antibody model in the jar of salt and iron filings, just on top of the mixture.
  1. Put the lid tightly on the jar and invert the jar about 10 times, as you did in step 5 of the Preparing the Immune System Model section. Remember, each inversion should last for about 1 s.
  2. Then carefully take the antibody out of the jar.
    1. You may want to carefully tilt the jar so you can reach the antibody.
    2. Hold the antibody by the twist tie or by the twisted plastic wrap. You do not want to touch the antibody where the iron filings are because this could affect your results.
    3. As you take the antibody out of the jar, be sure to gently turn it upside down so that any salt trapped in the twisted plastic wrap falls back into the jar. You may need to gently shake it to do this, but try not to let the iron filings get knocked off of the magnet. If a few do fall off, it is ok; continue with the science project.
  3. Observe the bottom of the antibody (the opposite side of the twist tie) by holding it up. Are there more iron filings stuck to the magnet than salt? Does it look like the antibody is specifically binding to the pathogens (the iron filings)?
    1. Write your observations in your lab notebook.
  4. Use the scale to weigh the iron filings and salt that are stuck to the antibody. There are a couple of ways you can do this:
    1. One method is to weigh the iron filings and salt directly on the scale:
      1. Put the piece of paper you folded in step 2 onto the scale and zero out the scale (so it says "0 grams").
        1. Note: If your scale does not have this function, first weigh the piece of paper; later you will need to subtract the paper's weight from your total weight with the iron filings and salt.
      2. Hold your antibody over the middle of the paper while you untie the twist tie and open up the plastic wrap surrounding the magnet. Carefully aim it so that the iron filings and salt only fall onto the paper.
      3. Read the scale and write the number (in grams) in your data table in the "One Antibody Alone" column for Trial 1.
        1. Tip: If you are having trouble reading the scale because the paper is so big, you can carefully fold up the paper's edge to better read it.
    2. Alternatively, if you are using a scale that turns off quickly when it is not being used (or you just want to take your time with this step), you can weigh the iron filings and salt by transferring them from a paper onto the scale:
      1. Put the piece of paper you folded in step 2 onto a flat surface (not onto the scale).
      2. Do step 7.a.ii.
      3. Place a small tray, a lightweight disposable bowl, or a folded piece of paper onto the scale and zero out the scale (so it says "0 grams").
        1. Note: If your scale does not have this function, first weigh the small tray; later you will need to subtract the tray's weight from your total weight with the iron filings and salt.
        2. Note: If you are using the Fast Weigh MS-500-BLK Digital Pocket Scale, it comes with a small tray that you can use for this.
      4. Then carefully pour the iron filings and salt (from the paper) onto the scale, into the small tray. Read the scale and write the number (in grams) in your data table in the "One Antibody Alone" column for Trial 1.
    3. Note: If you have a camera, you could take a picture of the iron filings and salt that the antibody removed from the infected tissue while they are on the piece of paper. Later, you could print this picture and put it on your Project Display Board.
  5. Carefully pour all of the iron filings and salt (that were pulled out by the antibody) back into the jar.
  6. Repeat step 4.
  7. Repeat steps 3–9 two more times.
    1. In step 7, continue to record your data in the "One Antibody Alone" column in the data table in your lab notebook, but record each time as a different trial (in a different row).
  8. Repeat steps 3–10, but this time in step 3 put three magnetic tape squares in the jar (instead of just one alone), as shown in Figure 10 below. This time record your data in the "Three Antibodies Together" section of the data table in your lab notebook.
    1. Do steps 5–8 separately for each antibody, one at a time (in other words, do not weigh the salt and iron filings from all three antibodies together; weigh and record the measurements separately).
    2. In the data table in your lab notebook, pick one antibody to be the "1st antibody," a different one to be the "2nd antibody," and the last antibody to be the "3rd antibody."
    3. Be sure to record your results in your data table in the correct columns and rows.
Human Biology science project Picture of three magnetic tape squares ('antibodies') in a jar of salt and iron filings.
Figure 10. Once you have tested one antibody alone in three trials, then test all three antibodies together in another three trials.

Analyzing Your Data

In this part of the science project, you will analyze your data and determine whether using one antibody alone was just as effective as using three antibodies together, or whether using three antibodies together was more effective than one alone.

  1. In the data table in your lab notebook, add together the numbers for each antibody in the "Three Antibodies Together" section for each trial. Write this number in the "Total" column in the data table.
    1. For example, if in Trial 1 the 1st antibody removed a weight of 3.2 g from the infected tissue, the 2nd antibody removed 2.7 g, and the 3rd antibody removed 3.5 g, then you would write 9.4 g as the total (3.2 g + 2.7 g + 3.5 g = 9.4 g).
  2. In your data table, calculate the average amount that each antibody removed from the jar in the "Three Antibodies Together" section for each trial. Write this number in the "Average" column in the data table.
    1. For example, if the total for Trial 1 was 9.4 g, the average would be 9.4 g divided by 3 (since there were 3 antibodies), or 3.1 g.
  3. Make a bar graph of how much weight the antibodies removed from the jar. Include the trials for one antibody alone, the total of three antibodies together, and the average of three antibodies together.
    1. You can make a graph by hand or use a website like Create a Graph to make a graph on the computer and print it.
    2. Put the weight (in grams) on the y-axis (the vertical axis going up and down). Put the data from the three trials for one antibody alone, the trials for the total of three antibodies together, and the trials for the average of three antibodies together, all on the x-axis (the horizontal axis going across).
      1. This means you should have nine bars total: Three for the one antibody alone trials, three for the total of three antibodies together trials, and three for the average of the three antibodies together trials.
  4. Look at your observations, data table, and graph and try to draw conclusions from your results.
    1. When the antibodies were exposed to the infected human body (the magnetic tape square was mixed with the iron filings and salt in the jar), did the antibody bind specifically to the pathogen (the iron filings)? Or did it bind to the pathogen and human cells (the salt) equally?
      1. What does this tell you about how selective your antibodies are, and the self/non-self recognition process in your model?
    2. Based on the results in your graph, does it look like one antibody alone was just as effective as three antibodies together, or were the three antibodies together more effective than the one antibody alone?
      1. You will want to compare the "Total" of the three antibodies together to one antibody alone. Did the three antibodies together usually remove a greater total amount than the one antibody alone did?
      2. You will also want to compare the "Average" of the three antibodies together to one antibody alone. Did the three antibodies on average usually remove a greater amount than the one antibody alone did, or were these amounts roughly equal?
    3. What do you think your results tell you about why the immune system creates memory cells? Why is it useful and effective to have memory cells?

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Variations

  • How could you tweak the model used in this science project to model differences in the immune response? For example, if you want to investigate antibodies that are more effective, you could try using larger or stronger magnets.
  • In this science project, you may have noticed that a small amount of salt was captured by the antibodies. In your model, this would represent the antibodies attacking the human cells in a type of autoimmune response. You could investigate the autoimmune response more by quantifying (measuring) how much salt was captured compared to the total amount (including iron filings) that was caught by the antibody. To do this you could carefully separate the salt that was caught from the iron filings that were caught by spreading both over a piece of paper and holding the plastic-wrapped magnet square right above them to pull out the iron filings. Then deposit the iron filings onto another piece of paper. Weigh the salt and iron filings separately. How much of each is there? What percentage of each (out of the total) is there? You could investigate whether certain factors affect this, such as having more or less salt or iron filings in the jar.
  • Try adding more than three antibodies to the jar at a time. Do your results change if you use more and more antibodies? Is there a certain number of antibodies at which you notice this change?
  • Can you think of other ways to model some part of the immune system? Tip: You will probably need to read more about the immune system to create a representative model of it. You could again try using magnets to represent the antibodies and iron filings to represent the pathogens.

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