Innate Immunity: Fighting Ebola

Biology Innate Immunity: Fighting Ebola With currently no approved drugs or vaccine for the Ebola virus, the more we understand about how the body fi...
Author: Oliver Walton
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Biology

Innate Immunity: Fighting Ebola With currently no approved drugs or vaccine for the Ebola virus, the more we understand about how the body fights this pathogen naturally, the better our chance of synthesising a treatment. In this lesson you will investigate the following: • What causes infectious disease? • How do we protect ourselves from microscopic invaders? • How does the innate immune response tackle viruses? • When is fever helpful? Aaaahhhhchoooo! Find out what your immune system is doing when you don’t feel like doing anything.

This is a print version of an interactive online lesson. To sign up for the real thing or for curriculum details about the lesson go to www.cosmosforschools.com

Introduction: Innate immunity (P1)

Dying from Ebola virus disease is a truly awful experience. First you get a fever and feel exhausted. Your muscles ache. You have a headache and a sore throat. Then you get diarrhoea and start vomiting. In some cases the virus destroys your blood vessels and you start bleeding from your nose, eyes and ears. Where did this terrible infectious disease come from? The first known human cases of Ebola occurred in 1976 in Sudan and the Democratic Republic of Congo. Scientists think that humans first contracted the disease from bats that carry the viral pathogen. Many poor people in Africa eat bats and any other “bush meat” they can find in the jungle. Fortunately the disease doesn’t affect humans all the time. An outbreak spreads, it kills many people, but then disappears, sometimes for years. But the current outbreak, which has killed nearly 6,000 people, is still going on. People catch Ebola when the virus enters their bodies through broken skin or through mucous membranes, like in your nose or mouth. So far there is no treatment or vaccine to protect people from the virus, and so world health authorities can only try to control the disease – preventing new cases by separating the sick from the healthy. That is harder in poor countries like those in West Africa than developed countries that have better roads and communications systems. In Africa, many people live in remote areas where it is hard for the authorities to know what is going on. Now the race is on to find both a treatment that will help more people survive the disease (at the moment about half of the people who contract the disease die from it) and also to find a vaccine, that will stop people catching it in the first place.

Read or listen to the full Cosmos magazine article here.

Question 1 Speculate: Ebola is a re-emerging infectious disease. There are many other infectious diseases that are either emerging or reemerging, as depicted in the map above. Describe some of the factors you think might be responsible for emergence or re-emergence of a disease.

Gather: Innate immunity (P1)

While all microscopic, microbes come in all sorts of shapes and sizes. Viruses (left) are the smallest and need other organisms to reproduce. Bacteria (middle) and protozoa (right) are larger than viruses and can reproduce by themselves. Do you notice any other differences?

Pathogens Pathogens are micro-organisms or microbes (organisms too small to be visible to the naked eye) that cause infectious disease. The most common infectious disease-causing microbes are bacteria, viruses, fungi, and protozoa (a type of parasite).

Question 1 Research: The illustration below shows four infectious diseases (left) and four microbe types (right). Draw lines to connect each infectious disease with the microbe type responsible for it. Hint: A simple internet search will help you.

Did you know? Not all microbes cause disease. Millions of microbes live on and inside our bodies without us even noticing and some types of microbes are even helpful. In Cosmos lesson 19 you can learn about the important ecosystem of microbes existing in our bowels.

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Question 2 Recall: Why does a virus need another cell for its growth?

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Question 3 Explain: The video clip showed that viruses have "keys" (ligands) and that cells have "locks" (receptors). Explain why it is essential for the ligand on a virus to bind to a specific cell receptor for a virus to infect it.

So when a virus gets inside you and infects one cell, millions of new ones come out of it. Then each of those new viruses do the same. Wouldn't that eventually kill you? Well it would, if it weren't for your immune system.

The immune system Your body is constantly being exposed to disease-causing microbes. Fortunately your immune system responds to any object, such as a pathogen, that it considers as foreign or ‘non-self’. In simplest terms, your body’s defence to pathogens can be divided into two types – the innate and adaptive immune systems. The innate immune system refers to the first line of defence of a host against a pathogen. It includes physical and chemical barriers to infection – non-specific defences ready and waiting to stop infections before they can set in. The adaptive immune system refers to the final line of defence against a pathogen. It involves the production of specialised cells and chemical substances called antibodies that target pathogens that managed to survive the innate immune system.

Innate immune system response to viruses Even though all viruses want to spread, many viral infections are prevented by the innate immune system. Some of these innate defence strategies are always in place including the skin and phagocytic cells; whereas others are triggered by an infection, such as fever and inflammation.

The skin

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Question 4 Calculate: The outermost layer of your skin (stratum corneum) consists of about 15 layers of dead cells. Together these cells measure approximately 0.0002 cm in thickness and yet, if intact, these cell layers are an excellent first line of defense against pathogens. Given that a typical A4 piece of paper is approximately 0.1 mm thick, calculate how many times thinner the stratum corneum is than A4 paper.

Phagocytic cells

Question 5 Sequence: Phagocytosis refers to the process by which an immune system cell engulfs a pathogen and digests it, thereby destroying it. The graphic below illustrates the process of phagocytosis by a phagocytic cell (also known as a phagocyte). Use the information in the graphic to sequence the stages (1-5) of virus phagocytosis. Sequence

Stages of phagocytosis Virus is destroyed by enzymes Phagocyte engulfs virus and traps it in a phagosome Waste is released from phagocyte Receptors on phagocyte recognise virus ligands as foreign molecules Phagosome fuses with lysosome sac which contains powerful enzymes.

Inflammation Viral infection can trigger the release of cytokine molecules. These molecules trigger inflammation by changing the permeability (leakiness) of surrounding blood vessels and so allow more immune system cells, such as phagocytes, to access the site of infection. As more and more cells and fluid from the blood vessels enter the surrounding area, the area becomes red, swollen and hot – we call this response inflammation.

Question 6 Compare: The graphic on the left illustrates a normal blood vessel, while the graphic on the right shows the same blood vessel during an inflammatory response. Draw green arrows to point to three changes that have occurred in the inflamed blood vessel and use the green text tool to describe each of these changes in your own words.

Fever Fever refers to a prolonged increase in your core body temperature above the normal range of 36.5–37.5°C. Many viruses, and other human pathogens, replicate best within host cells at a temperature of 37°C. So to fight them off your body raises its temperature so that it is too hot for the viruses to survive. The following data tracks the core body temperature of a person during the course of a virus infection.

Time following virus infection (hours)

Core body temperature (°C)

0

36.5

1

37.0

2

36.5

3

38.0

4

39.4

5

40.1

6

41.0

7

41.0

8

40.6

9

39.0

10

38.0

11

37.1

12

36.6

Question 7 Plot: Visualise the change in temperature over time above by plotting the above data as a smooth line. Hint: Be sure to label the x and y axes and to add a suitable title.

Title auto

Series 1

Y-Axis

x

This graph needs some data!

36

auto

auto

X-Axis

y

Question 8 Analyse: How many hours following infection by the virus did the fever begin and approximately how long did it last?

Question 9 Summarise: What innate immune system processes occur in the body in response to infection by a virus?

Process: Innate immunity (P1)

Ebola

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The Cosmos article “Ebola: no quick solutions” points out that there is currently no cure or approved treatment for Ebola. Malaria, for which we do have a cure kills over 100,000 people per year while Ebola has only ever killed 7034 people in total.

Poll 1 Which infectious disease, Ebola or Malaria, do you think should receive more media attention?

Ebola Malaria

Cumulative mortalities from Ebola 2014

Cumulative deaths

5k

4k

No data to display.

3k

2k

1k

0k

0

25

50

75

100

125

150

175

200

Days since first reported deaths

Question 1 Interpret: Which of the following best describes the trend line of the above line graph? Exponential Logarithmic Linear

Question 2 Calculate: Complete the following table by calculating the time (in days) for the number of mortalities to double. Days since first reported death

Number of deaths reported

Time (in days) for number of mortalities to double

76

250

N/A

105

500

29

139

1000

162

2000

198

4000

Question 3 Calculate: Determine the mean average time (in days) for number of mortalities to double.

Question 4 Predict: Using your above calculations, use the table below to calculate the number of days that it would take for the number of Ebola deaths to reach more than 100,000 if the current mortality rate stays constant. Days since first reported death 198

Mortalities 4000

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Poll 2 Having done the above calculations have you changed your mind? Vote again: Which infectious disease, Ebola or Malaria, do you think should receive more media attention?

Ebola Malaria

Question 5 Reflect: The World Health Organisation has claimed that “Busting the myths about Ebola is crucial to stop the transmission of the disease”. What roles do you think that journalists and science communicators should play in tackling the Ebola outbreak?

Question 6 Discuss: A recent survey has revealed that almost a third of US adults get at least some of their news from Facebook. Some research scientists, who study how we communicate on social networks, say people are more likely to trust information that comes from people they know. What advantages and limitations can you identify for communicating science news through social media? Add your thoughts to the class discussion below. Hint: If the class discussion is closed, ask your teacher to open it.

Apply: Innate immunity (P2)

Experiment: Modelling fever

Background The Cosmos article “Ebola: no quick solutions” outlines the signs and symptoms of Ebola disease. One of these symptoms is a high fever. Many scientists think that fever is an evolutionary adaptation to help survive pathogen attacks. Yeast is a unicellular eukaryotic microbe. Some species can be pathogenic but the majority are useful. Healthy yeast cells carry out a chemical process called fermentation, producing ethanol and carbon dioxide – the gas that makes bread rise and beer fizzy. Sugar solution provides the nutrition and energy that yeast requires to carry out fermentation, however there is an optimum temperature range and fermentation drops off at temperatures outside this range.

Aim Design an experiment to investigate the optimal temperature range for baker’s yeast (Saccharomyces cerevisiae) to carry out fermentation. The experiment is intended to model the response of a microbe to fever.

Materials 5 snack-sized zip-lock bags, each containing 2 g of baker’s yeast and 5 g of white sugar, labelled A - E 50 mL measuring cylinder 200 mL beaker 1000 mL beaker Thermometer (0 – 110oC) Hot water (approximately 80oC) Cold water (approximately 10oC) Ruler Note: You may not need all these materials, and you may want to use some other materials as well.

Variables Independent variable (what you are changing): The temperature of water added to each zip-lock bag. Dependent variable (what you are measuring): How much carbon dioxide is produced.

Inquiry questions For your experiment you will need to consider each of the following points: 1. What temperatures should you test the yeast at? 2. How will you ensure that the water remains at approximately the temperature you choose? 3. How you will measure how much carbon dioxide is produced? (Hint: you can obtain an approximation by rolling the bags from the top down and measuring the height of the gas – but you may be able to find a better technique.) 4. How long will you leave the yeast to ferment before you measure how much gas it has produced? Will you measure at different time intervals or only once, at the end of the experiment? 5. How will you make sure that your experiment is controlled? That is, how you will keep the conditions in each of the zip-lock bags the same to ensure the reliability of the experiment? 6. What will be your hypothesis for this experiment?

Procedure Question 1 Design: Write a step-by-step experimental method to show how you will test the effect of temperature on yeast fermentation. Ask your teacher to approve your plan before carrying it out.

Question 2 Complete: Describe how you will measure the dependent variable. List the controlled variables and describe how you will control them. Independent variable

Dependent variable

Controlled variables

The temperature of water added to each zip-lock bag.

Hypothesis Question 3 Judge: Predict what you think the outcome of your experiment will be, and why, by writing a hypothesis.

Safety considerations Question 4 Assess: Describe the potential hazards associated with the materials and method used in your experiment. How will you minimise risk from these hazards? Hazard

Risk minimisation strategy

Results

Question 5 Collect: Use the project space below to present your results. Construct a table to suit the data, but also include photos, video or other representations as you see fit.

Discussion Question 6 Justify: Explain why the same quantity of yeast and sugar was added to each zip-lock bag.

Question 7 Assess: Explain whether or not you think the yeast is affected by the change in temperature of the water added to each zip-lock bag. Use your results to support your answer.

Question 8 Generalise: In science, a model may be used when it is impossible to create the conditions necessary to investigate a concept or theory. In what ways do you think this experiment models the response of a microbe to fever?

Question 9

Question 10

Reflect: Identify some limitations of using this experiment to

Evaluate: Suggest improvements that you could make if you

model the response of a microbe to fever.

were to repeat this experiment.

Conclusion Question 11 Conclude: Write a concluding statement addressing the aim and hypothesis of your experiment.

Career: Innate immunity (P2)

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Question 1 Imagine: ​Which aspect of being an immunologist would you enjoy the most? Which would you enjoy the least?

Cosmos Lessons team Lesson authors: Hayley Bridgwood and Samantha Webber Editors: Jim Rountree and Bill Condie Art director: Robyn Adderly ​Education director: Daniel Pikler Image credits: Kate Patterson / Medipics and prose, Mirela Tufman and iStock Video credits: National Academies, NPR, MinuteEarth, AFP News Agency, Kurzgesagt and YouTube

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