Biology • Year 12 • Module 8 • Lesson 16
Autoimmune Diseases and Allergies
Lock in core vocabulary, distinguish the self-tolerance failure mechanism from IgE-mediated hypersensitivity, and connect named diseases to their immune targets.
1. Label the IgE-mediated allergy mechanism
The diagram below shows the two-stage mechanism of Type I hypersensitivity. Write the missing labels into boxes A–H. Each answer is drawn from the lesson's Key Terms or the process-step descriptions in Card 3. 8 marks
| Box | Your label |
|---|---|
| A | |
| B | |
| C | |
| D | |
| E | |
| F | |
| G | |
| H |
2. Term–definition match
The definitions below are shuffled. Write the matching term from this list in the right-hand column: autoimmune disease, self-tolerance, allergen, IgE, mast cell, histamine, anaphylaxis, clonal deletion, molecular mimicry, desensitisation. 10 marks
| # | Definition (shuffled) | Matching term |
|---|---|---|
| 2.1 | The immune system's ability to recognise and avoid attacking the body's own cells, maintained chiefly by clonal deletion in the thymus. | |
| 2.2 | A non-infectious disorder in which immune effectors attack self-tissues due to failure of immune self-recognition. | |
| 2.3 | A normally harmless environmental substance (e.g. pollen, peanut protein) that triggers an exaggerated immune response in a sensitised person. | |
| 2.4 | The antibody class produced against allergens; binds to mast cells and basophils, sensitising them for rapid degranulation on re-exposure. | |
| 2.5 | A tissue-resident immune cell that stores chemical mediators in granules and releases them rapidly when surface-bound IgE is cross-linked. | |
| 2.6 | A chemical mediator released during allergic reactions that causes vasodilation, increased vascular permeability and bronchoconstriction. | |
| 2.7 | A severe, life-threatening systemic allergic reaction involving massive, body-wide mast cell degranulation, causing cardiovascular and respiratory collapse. | |
| 2.8 | The thymic process by which T lymphocytes that react strongly to self-antigens are destroyed before they can circulate. | |
| 2.9 | A mechanism by which a pathogen antigen resembles a self-antigen; antibodies raised against the pathogen may therefore accidentally target host tissue. | |
| 2.10 | An allergy treatment that administers escalating doses of the allergen to shift the immune response from IgE (Th2) to IgG (Th1/Treg); the only disease-modifying allergy treatment. |
3. True or false — with correction
Circle T or F. If the statement is false, write the corrected version on the line below. 8 marks (1 T/F + 1 correction where needed)
3.1 Autoimmune disease is caused by a weak immune system that cannot respond to pathogens. T / F
3.2 Anaphylaxis can occur on a person's very first exposure to an allergen, before any IgE has been produced. T / F
3.3 Antihistamines work by preventing mast cells from releasing histamine into the surrounding tissue. T / F
3.4 In Type 1 Diabetes, the immune system destroys the beta cells of the pancreatic islets, causing absolute insulin deficiency. T / F
4. Function recall
Answer each question in 1–2 sentences using precise lesson terminology. 10 marks (2 each)
4.1 What is the function of clonal deletion during T-cell development in the thymus?
4.2 What is the function of IgE antibodies in sensitising a person to a specific allergen?
4.3 What is the function of intramuscular adrenaline (epinephrine) in treating anaphylaxis?
4.4 What is the function of regulatory T cells (T-reg cells) in maintaining immune tolerance?
4.5 What is the function of biologic therapies such as anti-TNF-α in treating autoimmune diseases?
5. Build a concept map
Draw labelled arrows between the six terms below. Each arrow must carry a linking phrase (e.g. "triggers", "leads to", "prevents", "releases"). Aim for at least 6 labelled arrows. 6 marks
Supplied terms: self-tolerance · autoimmune disease · IgE · mast cell degranulation · histamine · anaphylaxis.
6. Cloze — fill in the blanks
Complete the paragraph using words from the word bank below. Each word is used once. 8 marks
Type I hypersensitivity occurs in two stages. During _______________, first contact with the _______________ causes B cells to produce _______________ antibodies, which bind to the surface of _______________ in tissues. On re-exposure, the allergen cross-links these antibodies, triggering _______________ — the rapid release of pre-formed chemical mediators. The key mediator, _______________, causes _______________ (widening of blood vessels) and _______________ (narrowing of airways). When this reaction becomes systemic, it is called _______________, treated as a medical emergency with intramuscular _______________.
Q1 — Labelled allergy mechanism diagram
A: allergen (a normally harmless foreign substance). B: IgE (immunoglobulin E). C: mast cell (tissue-resident cell that binds IgE via high-affinity Fc receptors). D: mast cell degranulation (cross-linking of two adjacent IgE molecules triggers rapid release of granule contents). E: histamine (the primary pre-formed mediator responsible for immediate symptoms). F: vasodilation (increased vessel diameter → redness, heat, lowered blood pressure). G: bronchoconstriction (smooth muscle contraction in airways → wheeze, difficulty breathing). H: anaphylaxis (life-threatening systemic reaction; treat with IM adrenaline).
Q2 — Term–definition matches
2.1 self-tolerance · 2.2 autoimmune disease · 2.3 allergen · 2.4 IgE · 2.5 mast cell · 2.6 histamine · 2.7 anaphylaxis · 2.8 clonal deletion · 2.9 molecular mimicry · 2.10 desensitisation.
Q3 — True / false with correction
3.1 False. Correction: autoimmune disease is caused by an overactive or misdirected immune system — one that attacks self-tissues. The immune system is functional but has lost self-tolerance; it is not deficient.
3.2 False. Correction: anaphylaxis requires prior sensitisation. The first exposure produces IgE antibodies that bind to mast cells; anaphylaxis can only occur on a subsequent exposure when the allergen cross-links pre-bound IgE.
3.3 False. Correction: antihistamines block H1 histamine receptors on target cells (preventing histamine from binding) — they do not prevent mast cells from releasing histamine. Mast cell stabilisers (e.g. cromoglicate) prevent histamine release.
3.4 True.
Q4 — Function recall answers
4.1 Clonal deletion: Clonal deletion destroys T lymphocytes in the thymus that react strongly to self-antigens before they can enter circulation, preventing those autoreactive clones from attacking the body's own tissues and maintaining self-tolerance.
4.2 IgE in sensitisation: IgE antibodies, produced by B cells after first allergen exposure, bind with high affinity to receptors on mast cells and basophils. This "loads" these cells so that a second allergen contact causes rapid degranulation — the individual is now sensitised with no symptoms yet occurring.
4.3 Adrenaline in anaphylaxis: Adrenaline acts via alpha-adrenergic receptors to cause vasoconstriction (reversing the dangerous blood pressure drop) and via beta-receptors to cause bronchodilation (opening constricted airways) and increase cardiac output — directly reversing the three life-threatening effects of massive histamine release.
4.4 T-reg cells: Regulatory T cells (T-regs) suppress self-reactive lymphocytes that escaped clonal deletion, providing a second checkpoint for self-tolerance. If T-regs malfunction, self-reactive clones can proliferate and attack host tissue, contributing to autoimmune disease.
4.5 Anti-TNF-α biologics: Anti-TNF-α monoclonal antibodies (e.g. adalimumab) bind and neutralise tumour necrosis factor-alpha, a pro-inflammatory cytokine central to tissue destruction in diseases such as rheumatoid arthritis. By blocking this specific mediator, they reduce joint inflammation with fewer global immunosuppressive side effects than corticosteroids.
Q5 — Sample concept map
Correct maps should include arrows such as:
- self-tolerance — failure of leads to → autoimmune disease
- allergen (re-exposure) — cross-links surface → IgE
- IgE — cross-linking triggers → mast cell degranulation
- mast cell degranulation — releases → histamine
- histamine — if systemic, causes → anaphylaxis
- self-tolerance — maintained by clonal deletion and T-reg cells, preventing → autoimmune disease
Award 1 mark per biologically correct labelled arrow (maximum 6).
Q6 — Cloze answers (in order)
sensitisation · allergen · IgE · mast cells · degranulation · histamine · vasodilation · bronchoconstriction · anaphylaxis · epinephrine