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Navigating the challenges of Immunology

Jen Huang

When asked about what they loved or found challenging in the VCE Biology course, most Connecties agree that Immunology – of Unit 3 AOS 2 – fits in both categories. The scope and depth of this topic, and the level of detail assessors want to see on the page, definitely makes mastering it a big ask.

With that said, understanding how all the complex moving parts fit together is incredibly rewarding, not just in terms of your SAC marks, but also because it will give you a great head start on university level Biology.

In this article, we’ll unpack the commonly examined immunology topics in SACs and exams, highlight often-neglected (but important) things to know, and help you test your knowledge with targeted comprehension questions. Of course, this is only a guide – your teacher’s advice and the VCE Biology study design are extremely valuable sources of information – but we hope that our first-hand student experience can give you a hand, too.

Pathogens

Usually, pathogen-related content is examined in the form of rapid-fire, recall-based multiple choice questions, or as the first few parts of an extended response question leading up to a description of adaptive immune responses.

Also be prepared to link pathogen-related content to more complex immunological processes.

Quiz yourself:

  • The bacterial capsule masks bacterial antigens. How might this increase the pathogenicity (capacity to cause disease) of encapsulated bacteria?
  • How are intracellular infections detected by the immune system?
  • What are some innate immune defences against multicellular parasites?

Innate immune responses

Innate vs adaptive immunity

It’s definitely important to know your comparisons between innate and adaptive immunity.

Quiz yourself:

  • How does innate immunity differ from adaptive immunity in terms of duration, immunological memory and how long it takes to activate in response to an infection?
  • What kinds of white blood cells (leukocytes) are involved in innate immunity? How about in adaptive immunity?

First and second lines of defence

Understanding the difference between, and being able to list components of, first (fixed barriers) and second (activating in response to an infection or injury) lines of innate immune defence is crucial. This is usually assessed via multiple choice questions, but a multi-part short answer question could easily ask you to identify an innate immune barrier for one mark, and describe how it protects the body from infection for another.

Phagocytosis and the inflammatory response

These are the big ‘processs’ of the innate immune system (whereas the ‘processes’ for the adaptive immune system are hypersensitivities, humoral and cell mediated responses).

Phagocytosis – the process by which phagocytes ingest and destroy pathogens – is a crucial process of innate immunity, while the inflammatory response is really what ties all the different elements of the innate immune system together into one interactive order of events.

Quiz yourself:

  • Which cell types are capable of performing phagocytosis? Which of these cells have both MHC I and II markers on their plasma membranes, and what is the significance of these cells?
  • How do phagocytes recognise pathogens?
  • Can you diagrammatically represent the process of phagocytosis?
  • What are the roles of each of the following components in the inflammatory response?
    • Complement proteins
    • Neutrophils
    • Macrophages
    • Dendritic cells
    • Histamine
    • How does the inflammatory response help the adaptive immune response occur?

Cytokines

Finally, don’t forget that cytokines are the messengers used by the innate immune system to communicate. An exam-style question integrating different topics of Unit 3 might ask you to link the mode of action of cytokines – a protein-based signalling molecule – to the signal transduction pathways you learned about earlier in Unit 3 AOS 2.

Antigens and antibodies

Structure

Antigens and antibodies have a very special structural relatioship: antigens are complementary and specific to the antigen binding sites of antibodies. VCAA-style questions really hone in on this: a fairly common multiple choice question will ask you to choose the antibody that matches the shape of an antigen shown on the surface of a pathogen.

You should also be confident with drawing the quaternary structure of antibodies.

Quiz yourself:

  • What is the highest level of protein structure displayed in an antibody?
  • What type of interaction or bond keeps the protein sub-units of an antibody together?
  • How are light chain sub-units arranged in relation to heavy chain sub-units?

Function

Antigens are molecules on the surface of pathogens that the immune system recognises and responds to. Make sure you are able to distinguish them from allergens, which are innocuous (non-harmful) molecules from the environment that provoke an excessive immune response called an allergic reaction.

Having a general understanding of what antibodies do definitely comes in handy too, especially in relation to the adaptive humoral response.

Quiz yourself:

  • What are the different functions of the variable (antigen-binding) and constant regions of an antibody?
  • What is an agglutination, and can you represent one diagrammatically?
  • Can you identify at least three ways antibodies can combat an extracellular pathogen like a bacterium?
  • Why are antibodies relatively ineffective at fighting intracellular viral infections?
  • How are monoclonal antibodies being used in the treatment of cancer, and why is the specificity of antibodies extremely advantageous in this context?

Adaptive immune responses

Humoral and cell-mediated responses

The chance that a detailed short answer question about either the humoral or the cell mediated response will pop up is quite high. And for good reason: getting a solid grasp on this part of the topic is definitely tough, and really helps teachers and examiners identify top-performing students.

While often taught as two completely separate processes, try learning humoral and cell mediated responses as two branches of the same response, beginning with the activation of a T cell by an antigen presenting cell. That way, you’ll be able to reduce the amount of information you’re trying to memorise for each process, and gain a better understanding about the similarities and contrasts of each one. Our definitive immunology guide explains and illustrates this to a T.

Quiz yourself:

  • What are differences and similarities between B and T lymphocytes?
  • Describe what is meant by ‘clonal selection’ of B and T lymphocytes. Despite having the same antigen specificity, what are some differences between the roles of effector and memory B and T lymphocytes that form during clonal selection?
  • Can you compare the target(s) of the humoral and cell mediated responses?
  • Can you diagrammatically outline the humoral and cell mediated response?

Immunological memory

Immunological memory is the mechanism behind vaccines, and the reason why after we get chicken pox once we rarely get it again. It’s a unique property of the adaptive immune response and often gets a spot on the end of year exam, either in the multiple choice or short answer sections.

Quiz yourself: 

  • Can you use a graph to compare the amount of antibodies produced by the body during a secondary immune response vs during a primary immune response? Why is there a difference?
  • Which 2 factors contribute to the increased amplitude and speed of the secondary immunological response compared to the primary immunologic response?

Immune disorders

Given the incredible complexity of the immune system, we can’t always expect it to work perfectly. Allergies and autoimmunity are the result of an inappropriately activated immune system, while immunodeficiency results when the immune system isn’t giving it 100%.

Often, the best way to learn about normal human function is to learn about what happens when things go wrong. So think about these immune disorders as specific case studies of the immune system’s importance and the function of certain immune components.

Quiz yourself:

  • Which antibody class and cell(s) are involved in the allergic response? Why is this response considered a ‘hypersensitivity’ reaction?
  • Can you describe the hypersensitivity reaction involved in hayfever (pollen allergy) in defined steps?
  • Which cells are targeted by HIV, and why does untreated HIV cause AIDS?
  • Can you use multiple sclerosis to explain why self-tolerance is an essential part of human immunity?

Summary

With these guidelines in mind, you can now clearly identify the parts of the topic you’re confident with, and the parts that you feel are more challenging. If you found answering some of the comprehension questions mentioned challenging, our definitive guide to immunology is for you. Here, we dive into the more challenging parts of the content, with detailed written explanations and original diagrams to deepen your understanding.

Without a doubt, immunology was my favourite part of the VCE Biology course. And with a now solid grasp of both the content and how the content is examined, it will fast become yours too.

 

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The ultimate immunology handbook. 

Complete with crystal clear explanations, original diagrams and exclusive questions. 

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