How Our Immune System and Vaccines Protect Us From Diseases

Background Information for Teachers

Our immune system is made up of different cells and organs that work to defend us against pathogens. Pathogens are microorganisms that make us sick. They include harmful bacteria (like Salmonella or E. coli, which cause food poisoning), microscopic fungi, viruses (ranging from measles to the flu), and more.

Once a pathogen enters our body, our immune system goes through a series of processes called the immune response. Any "foreign substance" that causes an immune response is called an antigen. Antigens can be entire pathogens, specific parts of a pathogen, allergens, toxins, or specific molecules. They function as markers that tell our immune system that something in our body is harmful.

Once our immune system encounters an antigen, an immune response is triggered. The immune response consists of two parts: the innate immune response and the adaptive immune response. The innate immune response is the first line of defense against pathogens and includes physical, chemical, and cellular defense mechanisms. The physical and chemical barriers consist of our skin and mucous membranes, which prevent pathogens from entering our bodies. Once pathogens breach these barriers, the innate immune cells are activated. These immune cells are special white blood cells that can detect invaders and destroy them. They include phagocytes, such as macrophages, neutrophils, and dendritic cells, as well as other cells called natural killer cells. The most important task of these innate immune cells is to detect a pathogen.

Innate immune cells have pattern recognition receptors—special proteins in and on their cell membranes that can detect molecules frequently found in pathogens. Once a pathogen is identified, the immune cell's receptor binds to the pathogen. Then the pathogen is destroyed. Using these pattern recognition receptors, innate immune cells can identify and quickly respond to a broad range of pathogens. The innate immune response is quick but non-specific. While it can recognize and destroy different types of pathogens, it cannot distinguish between them.

Once a pathogen slips through the innate immune response, the second line of defense is the adaptive immune response. The key players in the adaptive immune response are T cells and B cells. Like innate immune cells, T cells and B cells carry specialized receptors on their surfaces. The difference is that these receptors only bind to one specific antigen; they are antigen-specific.

The adaptive immune response is usually triggered by innate immune cells, specifically dendritic cells. When dendritic cells encounter a pathogen and destroy it, they display parts of the pathogen—its antigens—on their cell surface. Subsequently, any T cell with a matching antigen receptor gets activated and divides rapidly to produce many more T cells with the same T cell receptors.

Once activated, T cells can become either helper T cells or cytotoxic T cells. Cytotoxic T cells directly destroy cells infected with a pathogen in a process called cell-mediated immune response. Helper T cells, on the other hand, activate B cells with matching B cell receptors. Once activated, these B cells become plasma cells that produce antibodies—y-shaped proteins—which they release into the body.

Antibodies are our immune system's ultimate weapon against a specific pathogen. Each antibody consists of a conserved or constant region and a variable region, as shown in Figure 1. The tips of both y-arms contain variable antigen-binding sites. They are tailored to the specific antigen the immune system is currently fighting. Once an antibody encounters a matching antigen, it binds to it and flags it for destruction, as shown in Figure 2. This process of antibodies fighting a specific pathogen is called the humoral immune response. B cells continue to produce antibodies until the body is cleared of pathogens and the infection is over.

Image Credit: Wikimedia / Creative Commons Attribution 3.0 Unported

On the left, 12 rectangular shapes arranged into a y-shape show the basic structure of an antibody. The rectangles at the tips of the y have indentations representing antigen-binding sites. On the right, squiggly lines arranged into a y-shape respresent a more realistic visualization of the y-shaped protein structure of antibodies.

Figure 1. Schematic drawing (left) and protein structure (right) of an antibody. Image credit: OpenStax College, CC BY 3.0, via Wikimedia Commons.

Figure 2. 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 get help from white blood cells to destroy the pathogen. Note: These are simplified drawings that are not to scale.

Although the adaptive immune response is relatively slow—it can take up to several weeks to successfully fight an infection—it has one more powerful function: memory. While most B cells and T cells die after infection, some of them develop into memory cells. This usually happens during a primary immune response, which is the first time the immune system encounters a specific pathogen. Memory cells are able to remember a specific antigen and can quickly be reactivated when the immune system encounters the same pathogen again. As a result, the secondary immune response is usually much more rapid and powerful. Figure 3 provides an overview of the processes involved in the innate and adaptive immune responses.

Image Credit: Wikimedia / Creative Commons Attribution-Share Alike 4.0 International
Figure 3. Schematic overview of the processes involved in the primary immune response, including innate and adaptive immune cells. Image credit: Sciencia58 and the makers of the single images Domdomegg, [1], Fæ, Petr94, Manu5, CC BY-SA 4.0, via Wikimedia Commons.

Scientists have figured out how to harness our immune system to protect us from certain diseases. One major tool that has been developed in preventative medicine is the vaccine. Vaccines are a good way to build up immunity against certain diseases. They prime an individual's acquired immune system so it has antibodies to recognize and fight off a potential pathogen without ever having to experience the harmful or even deadly symptoms of the disease. Some vaccines contain inactivated viruses or bacteria. Others contain specific antigens of viruses or bacteria (or, in the case of mRNA vaccines, instructions to make the antigens). The vaccines trigger a primary immune response against that pathogen without causing an actual infection or disease. As a result, our body makes antibodies that are ready to help recognize and destroy the pathogen should we become infected for real.

Some vaccines offer long-term protection, but others have shorter effects. To protect us from the flu, for example, we need a new shot every year. Other vaccines, such as the COVID vaccine, need to be updated as well. This is in part because pathogens evolve to survive. Viruses, because of their short generation time, can be especially quick to evolve. Evolving means accumulating mutations in their genes. These genetic mutations can change the structure of their antigens. This process is called antigenic drift, and it can result in many different pathogen variants, each with a slightly different genetic makeup.

When a genetic mutation affects the antigen, the new pathogen variant becomes capable of escaping an existing immunity. The new antigens will no longer bind to the antibodies or immune cell receptors. As a result, the new virus variant is able to infect people who were immune to the original strain due to prior infection or vaccination. To counteract the antigenic drift of the influenza virus, a new flu shot is developed every year to cover new virus variants. Our immune system also evolves in an effort to outsmart new pathogens. This results in a constant arms race between our immune system and pathogens.

Additional Background Links

• The Immune System, HHMI, BioInteractive
• Videos & Animations, The Vaccine Makers Project
• The innate and adaptive immmune response, InformedHealth.org
• Vaccines and immunization, World Health Organization

Prep Work (10 minutes)

1. Print one student worksheet for each student.
2. Print one set of antigen cards and one set of antibody cards for each student group (in color). Cut along the lines to separate each antigen and antibody and place all the cut-out antigens and antibodies in a resealable plastic bag.
3. Print one set of vaccine factory cards for each student group.
4. Print out the pathogen notes for students and cut out each note.
5. Have the pathogen slides and the antibody structure slide ready to show to your class.
6. Optional: If you don't have your own reading materials for this lesson content, you can print out a student study guide for each student. It contains all the key points of the lesson in condensed form. You may want to distribute the study guide to students after class so they can review the lesson content before taking the quiz.

Engage (15 minutes)

1. Ask students to recall the last time they had an infection, such as the flu, a cold, COVID, or a stomach bug.

   Can you remember the last time you had an infection, such as the flu, a cold, COVID, or a stomach bug? What do you think caused your infection?

   Listen to students' responses. Point out that getting a cold, the flu, COVID, or a stomach bug is quite common. Then use students' responses to explain that we get sick when pathogens enter our bodies. Pathogens are microorganisms, such as bacteria or viruses, that can make us sick.

2. Continue discussing the symptoms of their infection.

   When you were sick, can you remember how you felt? What symptoms did you have?

   Make a list of symptoms students mention, such as fever, headache, aching body, congested nose (swelling), vomiting, diarrhea, etc. Tell students that these symptoms were all signs that their bodies were fighting against the infection and trying to get rid of the pathogen. Most of the time, our bodies can defeat the pathogen, and we recover from the infection fairly quickly.

3. Introduce the immune system and its response mechanisms to your students.

   Do you have an idea how our body fights infections and destroys invading pathogens?

   Have students share their thoughts. Focus on responses that mention that our immune system fights diseases and destroys invading pathogens. Explain to students that it is, in fact, our immune system that fights off harmful pathogens. Once it encounters a pathogen, the immune system triggers a series of processes called the immune response. Mention that the immune response consists of two parts. One is the innate immune response, and the other is the adaptive immune response. Briefly explain to students that the innate immune response is the first line of defense against pathogens and is initiated immediately after the pathogen attack.

4. Show students the Innate Immune Response video. Tell students to make notes about what they have learned about innate immunity on their worksheet.
5. To summarize what the innate immune response entails and what it does, ask students to use their notes on innate immunity to fill in the blank spaces in the innate immunity text on their worksheet. Key points about innate immunity that students should remember are:
   • Innate immunity is the first line of defense against pathogens.
   • The innate immune response happens very quickly after a pathogen attack (within minutes or hours).
   • Innate immunity includes physical and chemical barriers, such as our skin and mucous membranes, as well as innate immune cells.
   • Innate immune cells are special white blood cells called phagocytes that recognize and destroy invading pathogens.
   • Innate immune cells use pattern recognition receptors to tell foreign invaders apart from body cells.
   • Innate immunity is non-specific. Innate immune cells can recognize and destroy a wide range of pathogens but cannot distinguish between them.
6. Introduce the adaptive immune response. Tell students they should take notes on their worksheets about what they learn about the adaptive immune system throughout the lesson. Ask students what they think happens when pathogens slip through the innate immune response.

   What do you think happens if pathogens breach the first line of our immune defense and slip through the innate immune response?

   Have students share their thoughts. They might point out that the video mentions a more targeted defense once an invading pathogen gets past the innate immune response. Explain to students that this targeted immune response is called the adaptive immune response.

   The adaptive immune response is the second line of defense of our immune system. Certain innate immune cells activate the adaptive immune response while fighting pathogens. Point out that in contrast to the innate immune response, the adaptive immune response is specific, which means it can target specific pathogens. The key players of the adaptive immune response are T cells and B cells, which both fight pathogens, but in different ways. While T cells can directly kill cells infected with a pathogen, B cells produce antibodies that fight pathogens.

   Tell students that in the next part of this lesson, they will explore the adaptive immune response in more detail, specifically the critical role of antibodies in fighting off infections and pathogens.

Explore (60 minutes (Three 20-minute activities))

For the activities, divide the class into groups of 2-3 students.

Part 1: Explore antibody specificity with an "antigen and antibody matching" activity (20 minutes)

1. Tell students that they will now do an activity to find out why antibodies are such a powerful weapon against pathogens. Distribute one set of printed antigen and antibody cards (in color) to each student group. Explain that one set of cards shows a variety of antibodies, and the other set of cards shows a variety of pathogens with antigens on their cell surfaces. Explain to students that antigens are any foreign substances that trigger an immune response. Antigens can, for example, be special surface features or molecular structures on the pathogens' cell surface that our immune system can recognize as foreign. Ask students to look at both the antigen and antibody cards carefully. Give students five minutes to examine the cards. Then discuss what they observed.

   What observations did you make when looking at the antibody and antigen cards? What did you notice about the shape of the antibodies? How are the antibodies and antigens similar or different?

   Listen to students' replies. Use their replies to point out the antibody structure. Show students Figure 1, which shows what an antibody looks like, and explain to students that antibodies are y-shaped proteins that our immune system (more specifically, the B cells) produces to fight pathogens. Each antibody contains a conserved (constant) region and a variable region. The variable region is at both tips of the Y and contains the antigen-binding site. Students should have noticed that the antigen-binding sites of each antibody match only one of the pathogens on the antigen cards. (The matching antibody and antigen have the same color.) Tell students that each antibody is designed to bind only to one specific antigen. Antibodies and antigens work like a lock and key mechanism. Point out that this antibody specificity is what makes antibodies so powerful. Using highly specialized antibodies allows the immune system to specifically target one type of pathogen. Once the antibodies have found and bound their target antigen, the pathogen is flagged for destruction. Mention that, in contrast to the innate immune response, the adaptive immune response is relatively slow. The first time a pathogen is encountered, which is called the primary immune response, it usually takes about one week until antibody production against a pathogen starts.

2. Continue with the matching game. Tell students that you will simulate a pathogen invading their body and that they must produce the matching antibody against it as fast as possible. Explain that you will show them a picture of the pathogen that enters their body. Use the pathogen slide set for this purpose. They must find the right antibody from their antibody cards to match the antigen on the pathogen shown (see example in Figure 4). Once they have found the matching antibody, ask them to hold it in the air for everybody to see. The student group that finds the matching antibody card first gets one point. Play the game until you have shown 10 pathogen cards in total. If you like, you can give a prize to the winning student team.
   Image Credit: Svenja Lohner, Science Buddies / Science Buddies

   The left image shows a roundish shape representing a pathogen. On its surface are a circular shape and a truncated cone shape representing the pathogen’s antigens. The right image shows a y-shaped form representing an antibody. At both tips of the Y-shape, inverted circular and truncated cone shapes represent the matching antigen-binding sites of the antibody.

   
   Figure 4. Example of a matching antigen-antibody pair.
3. Once students have completed the activity, show them the Adaptive Immune System video, which summarizes what they have learned and provides more details about the adaptive immune response. Remind them to take notes on their worksheet about the adaptive immune response.
4. Highlight another powerful aspect of the adaptive immune response: Explain to students that during a primary adaptive immune response, which is the first time the immune system encounters a specific pathogen, memory cells are produced. These memory cells are immune cells, such as B cells and T cells, that are long-lived and have the ability to remember a specific antigen in case the immune system encounters it again in the future. If the same pathogen invades again, these memory cells enable the immune system to proceed immediately with a secondary adaptive immune response that is much faster and much more powerful.
5. To summarize what the adaptive immune response entails and what it does, ask students to use their notes on adaptive immunity to fill in the blank spaces in the adaptive immunity text on their worksheet. Key points about adaptive immunity that students should remember are:
   • The adaptive immune response is the second line of defense against pathogens.
   • The adaptive immune response is much slower than the innate immune response.
   • The adaptive immune response gets triggered by innate immune cells.
   • The key players of the adaptive immune response are T cells and B cells.
   • B cells produce antibodies, which are the immune system's ultimate weapon against pathogens.
   • Antibodies are y-shaped proteins. Their variable regions at both tips contain antigen-binding sites.
   • Antigens are any foreign substances that trigger an immune response. Examples of antigens are specific surface features or molecular structures on a pathogen's cell surface.
   • Antibodies only match one specific antigen. Antibodies and antigens work like a lock and key mechanism.
   • The first time the adaptive immune system fights a specific pathogen is called the primary immune response.
   • During a primary immune response, the adaptive immune system creates memory cells. Memory cells are long-lived B cells and T cells that can remember a specific antigen in case the immune system encounters it again in the future.
6. Move on to Part 2 of the lesson, which will introduce vaccines in the context of antibodies.

Part 2: Explore how vaccine-induced antibodies protect against disease with a "vaccine factory" activity (20 minutes)

1. Start a discussion about how we can protect ourselves from diseases and help our body fight pathogens. This includes introducing vaccines and their purpose.

   We just learned about how our immune system works and how important antibodies are for fighting pathogens. Can you think of a way that we could help our body fight pathogens? How could we use what we know about our immune system to protect ourselves from diseases?

   Have students share their ideas. Elicit responses that mention vaccines. If students have difficulties making the connection to vaccines, mention that for our bodies, the best defense against a pathogen would be to have the right antibodies in place even before the pathogen invades. Then point out that this is exactly what vaccines are for. Explain that vaccines present the body with a pathogen's antigens without making the individual sick. This is typically done in one of several ways: A vaccine that has weakened or otherwise inactive forms of the pathogen A vaccine that is made up of the pathogen's antigens A vaccine, like the COVID mRNA vaccines, that instructs the body to make the pathogen's antigens which it then produces antibodies against. All types of vaccines trigger a primary immune response against the pathogen without causing an actual infection or disease. As a result, our body makes antibodies that help recognize and destroy the pathogen that causes the disease once there is a real pathogen attack.

2. Have students name some vaccines that they know of. Examples include the vaccines against the flu, COVID, measles, chicken pox, tetanus, pertussis, HPV, etc. You can also show students the How the COVID mRNA Vaccine Works video.
3. Continue with the "vaccine factory" activity. Tell students that in the following activity, they will have to design a vaccine against a specific disease. The vaccine they will design can only contain specific antigens or parts of the disease-causing pathogen. Their task is to determine which antigen(s) or parts of the pathogen they need to include in the vaccine to be effective against the disease.

   Distribute one vaccine factory card set to each student group. Then give each student group a note that tells them which cell number is their disease-causing pathogen. Each group should design a vaccine for a different pathogen. Explain to students that on their cards they will find many different cells presenting different antigens on their surface. The note they received tells them which of the cells is the disease-causing antigen they need to develop a vaccine for. The other cells represent different body cells.

   Tell students that, based on these cards, they need to identify the correct antigen(s) for their vaccine so that after vaccination the immune system can create antibodies against their disease-causing pathogen. Remind them that antibodies need to be specific and should only target the pathogen that needs to be destroyed. If the vaccine-induced antibodies bind to cells other than the pathogens, this could have serious side effects.

4. Give students 10 minutes to complete their tasks. Tell them that they should draw the specific antigen(s) they have selected for their vaccine on their worksheet.
5. Once the 10 minutes are over, ask the students to stop. Then ask every group about their results. You might want to ask them the following questions.

   Tell us which pathogen (cell number) you were developing a vaccine for. Which antigen(s) did you choose for your vaccine? Can you explain why you chose this antigen?

   What did you find easy or difficult about choosing the antigen(s) for your vaccine?

   Have students either explain what their antigen looks like or draw the antigen they selected for their vaccine on the whiteboard. Students should have recognized that each single antigen symbol is not unique; it is present on several cells. Thus, the antigen they needed to choose for their vaccine was a combination of at least two different antigen symbols. Some student groups might have found it challenging to determine which antigen symbol combination is unique to their pathogen. For some cells, there exists more than one possible unique antigen. An example is shown in Figure 5. If students don't mention it themselves, emphasize again that the antigens they have selected should be unique for their pathogen and not target other cells simultaneously. This is crucial; otherwise, the vaccine-induced antibodies would also target other cells in the body.

   Image Credit: Svenja Lohner, Science Buddies / Science Buddies

   On the left, a circular shape represents a pathogen. Small rectangles, pentagons, and triangles on its surface represent the pathogen's antigens. On the top right are three unique antigen combinations for the pathogen. The left one shows a pentagon to the left of a traingle, the middle one shows a pentagon to the right of a rectangle, and the right one shows a pentagon in the middle, a triangle on the right and a rectangle on the left. Below the individual antigens the corresponding antibodies are shown. They are depicted as y-shapes with shapes at their tips that match their respective antigen.

   
   Figure 5. Possible unique antigens for cell #2 and their corresponding antibodies.
6. Ask students what their vaccine-induced antibody would look like. Have them draw it on their worksheet. An example is shown in Figure 5. Prompt them to check whether their antibody is specific to their pathogen and doesn't target any other cells.
7. Tell everyone that they did a great job in designing their vaccines. The vaccine-induced antibodies that they just drew on their worksheet are now ready to fight the pathogen once it attacks for real. Then mention that sometimes the fight against pathogens is not over with the development of a vaccine. Tell them that in the following activity, they will explore how some pathogens can escape existing immunities. Then move on to Part 3 of the lesson.

Part 3: Explore why sometimes vaccines need to be refreshed due to pathogen mutations with an "antigenic drift" activity (20 minutes)

1. Have students think about how pathogens could escape an existing immunity.

   You would think that after vaccination, our body should be immune to a specific pathogen forever. However, we need a new flu shot every year. Can you think of a reason why this is the case? How could a pathogen such as the flu virus escape the antibodies our bodies made after vaccination?

   Have students share their ideas. Students should mention that one way for pathogens to escape existing antibodies is by changing their antigens. Once their antigens don't match the existing antibodies anymore, the antibodies won't bind to them, and the pathogens will not be flagged for destruction. Tell students that this is exactly what happens in nature. Most pathogens evolve, which means that they change their structure, including their antigens, slightly over time. This process is called antigenic drift.

2. Continue with the pathogen mutation activity. Tell students that in the following activity, they will simulate what can happen if a pathogen mutates. Ask student groups to swap their notes—the ones that told them which cell of the vaccination factory cards was their pathogen—with another group. Each group should now have a different pathogen assigned to them. Tell students that their pathogen has just mutated. The pathogen they have now is a mutated version of their first pathogen. Some of its antigens might still be the same, but others might not. Have students evaluate whether their mutated pathogen (or pathogen variant) would be able to escape their vaccine-induced antibodies.

   Everybody should now have a new pathogen assigned to them. This new pathogen represents a mutated version of your previous pathogen, also called a pathogen variant. Look at your mutated pathogen closely. Based on its mutations, could your mutated pathogen escape your vaccination-induced antibodies?

   Students should check whether their previously developed vaccine-induced antibody would still be able to bind to their mutated pathogen. Most likely, the antibody will not be able to bind to the pathogen variant. Have students explain why their mutated pathogen could or could not escape their vaccine-induced antibodies. They should describe how the antigens on the pathogen changed and why the antibody does not match anymore. Use students' observations to point out that some pathogens evolve quite fast and that it sometimes can be challenging to keep up with new pathogen variants. Mention some examples, such as the influenza virus that causes the flu or the coronavirus that causes COVID.

3. Show students the Antigenic Drift: How the Influenza Virus Adapts video, which demonstrates how pathogen mutations, also called antigenic drift, can render existing immunities ineffective. Explain that what they call "surface keys" in the video are the pathogens' antigens. Stop the video at 1:51 minutes, when they start talking about antigenic shift.
4. Wrap up the Explore part of the lesson by discussing how we can counter antigenic drift.

   What do you think we can do to ensure we can still protect ourselves against pathogen variants that emerge due to antigenic drift?

   Have students share their thoughts. They might bring up the previously mentioned example of the annual flu shots. This means updating or adjusting an existing vaccine regularly to include the most recent pathogen variants. Mention that this is exactly why for some infections we need to refresh our vaccines regularly. Explain to students that it is very important to carefully monitor antigenic drift by investigating which parts of a pathogen mutate, how they mutate, and at what rate they mutate. Sometimes it is possible to identify a specific antigen that is more conserved than others, which means it doesn't mutate much compared to others. Such an antigen would be a good candidate for future vaccines.

5. Optional: If you have time, do the following "vaccine adjustment" activity in class. Otherwise, assign this part as homework for students. Explain to students that their task is to develop an adjusted vaccine that can target as many pathogen variants as possible. For this purpose, all the cells on their vaccine factory cards are now variants of the same pathogen. Some of the pathogens have similar antigens; some are different. Their task is to find the antigen(s) or develop a vaccine-induced antibody that can target as many pathogen variants as possible (an example is shown in Figure 6). Tell students to draw their adjusted vaccine antigen(s) and adjusted vaccine-induced antibody on their worksheets. Have them explain in their worksheet why they have chosen these antigen(s) for their adjusted vaccine and how many pathogen variants they can target with it.
   
   
   Image Credit: Svenja Lohner, Science Buddies / Science Buddies

   Each circle has various symbols, such as triangles, rectangles, arrows, etc., on its surface that represent different antigens. Matching pointed shapes are present among the antigens of six different cells.

   
   Figure 6. Schematic drawing of ten different pathogen variants. Symbols on their surface represent the pathogen's antigens. Red squares highlight an antigen that can target six pathogen variants simultaneously.
6. Continue with the Reflect part of the lesson.

Reflect (15 minutes)

1. Tell students that they have learned much about the immune system in this lesson, especially about the role of antibodies in fighting diseases. Ask students to summarize some of the key points they have learned today in their own words. These should include the following:
   • Our immune system fights pathogens that are invading our bodies. Its first line of defense is the innate immune response, which involves phagocytes (special white blood cells) that can destroy pathogens. The innate immune response happens quickly but is non-specific. The second line of defense is the adaptive immune response, which happens more slowly. During the adaptive immune response, B cells produce antibodies that target the invading pathogens specifically. In addition, memory cells are created, which allow for a more powerful and faster secondary immune response.
   • Antibodies are y-shaped proteins our body produces to fight pathogens. They have variable antigen-binding sites at each tip of the Y. Each antigen-binding site only matches one specific antigen. Antibodies and antigens work like a lock and key mechanism.
   • Because antibodies are so powerful due to their antigen specificity, they are a key component of vaccines. Vaccines expose our immune system to known antigens (such as the flu virus) without causing an infection. As a result, vaccine-induced antibodies can fight the disease-causing pathogen once it invades our body for real.
   • Pathogens can escape existing immunities by mutating their antigens, called antigenic drift. This is why we need to refresh some of our vaccinations regularly.

   At this point, you can give a student study guide to each student. The guide contains the lesson's key points in condensed form. Remind students that they can use this study guide to review the contents of this lesson before they take the lesson quiz.

2. Once you have summarized the key learning points of the lesson, emphasize that the arms race between pathogens and the immune system never ends. Many pathogens mutate very rapidly, which can become problematic for our immune system. This is why many researchers are trying to figure out how we can outsmart pathogens that continue to escape our immune system. Show students the following video, in which one researcher provides insight into his research in that field.
   

   https://www.youtube.com/watch?v=r6bMcNx4dfA

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3. Conclude the lesson by asking students if they have any questions about the video or the topic in general. Encourage students to do their own research and show them how to find the information they are looking for. Use the opportunity to introduce students to potential careers related to this field (listed below).

Assess

You can use this quiz to assess student learning after the activity:

• Online quiz, assignable in any LMS
• Quiz (pdf) and answer key (pdf)

In addition, the student worksheet can be used to evaluate students' understanding of the activities and basic concepts.

Make Career Connections

Discussing or reading about these careers can help students make important connections between the in-class lesson and STEM job opportunities in the real world.

Biochemist

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Career Profile

Growing, aging, digesting—all of these are examples of chemical processes performed by living organisms. Biochemists study how these types of chemical actions happen in cells and tissues. They could, for example, study how viruses replicate in a human cell or investigate how viruses make people sick. Using their knowledge about pathogens and biochemical processes in our bodies, biochemists often contribute to developing new vaccines. Read more

Bioinformatics Scientist

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Sequencing of genomes, an organism's complete set of genetic material, can help monitor genetic variation in populations of humans, animals, or viruses. It also generates a lot of sequencing data! Bioinformatic scientists work at the crossroads of biology and computer science and can help make sense of large amounts of sequencing data. They could, for example, use sequencing data to figure out how antigens in a virus change and how fast a virus mutates. Read more

Microbiologist

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Microorganisms (bacteria, viruses, algae, and fungi) are the most common life forms on Earth. They help us digest nutrients, make foods like yogurt and bread, and create antibiotics. Some microbes also cause diseases. Microbiologists study the growth, structure, development, and general characteristics of microorganisms to promote health, industry, and a basic understanding of cellular functions. Read more

Health Educator

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Have you ever heard the expression "Prevention is the best medicine"? Prevention is the fundamental work of all health educators. They attempt to prevent illnesses or diseases in individuals or entire communities through education about nutrition, exercise, or other habits and behaviors. Health educators could, for example, run programs that educate patients regarding vaccines and the diseases they prevent. Read more

Lesson Plan Variations

• Use what students have learned about the innate and adaptive immune response to discuss autoimmune disorders. Reflect with students on what would happen if our immune cells could not differentiate between foreign intruders and our own body cells anymore or if our immune system overreacted to harmless substances. Explain that allergies and autoimmune disorders result from an overreacting or misguided immune system. Provide examples of autoimmune disorders and discuss how they could be treated or prevented.
• Vaccines are not the only way that preventative medicine makes use of our immune system. In the last decades, new antibody therapies have been developed that include monoclonal and bispecific antibodies. These are bioengineered antibodies designed to target specific antigens involved in diseases. Discuss the application of monoclonal or bispecific antibodies and have students research some of the FDA-approved monoclonal or bispecific antibody drugs.