Biology • Year 12 • Module 8 • Lesson 16
Autoimmune Diseases and Allergies
Apply lesson mechanisms to real Australian data, case studies and diagram critiques — practice exam-style reasoning about immune dysfunction.
1. Interpret Australian autoimmune and allergy prevalence data
The table below shows estimated prevalence and annual healthcare cost data for selected autoimmune and allergic conditions in Australia (data adapted from Autoimmune Alliance Australia, 2022; ASCIA, 2023). 7 marks
| Condition | Type | Prevalence (est. % Australians) | Target tissue / allergen | Annual healthcare cost (AUD, approx.) |
|---|---|---|---|---|
| Rheumatoid arthritis | Autoimmune | 2.0 | Synovial membrane | $1.8 billion |
| Multiple sclerosis | Autoimmune | 0.3 | CNS myelin sheath | $1.2 billion |
| Type 1 diabetes | Autoimmune | 0.5 | Pancreatic beta cells | $2.1 billion |
| Allergic rhinitis (hayfever) | Allergy (IgE) | 18.0 | Airborne pollen / dust mite | $0.9 billion |
| Food allergy | Allergy (IgE) | 10.0 | Peanut, tree nuts, shellfish | $0.7 billion |
| Anaphylaxis (hospitalisations) | Allergy (IgE, severe) | 0.02 per yr | Various allergens | $0.15 billion |
1.1 Using data from the table, describe the pattern between prevalence and annual healthcare cost for the conditions listed. Is higher prevalence always associated with higher cost? Use at least two specific figures. 2 marks
1.2 Allergic rhinitis affects 18% of Australians but costs less per affected person than Type 1 diabetes (0.5%). Using your understanding of immune mechanisms, explain this difference in per-person healthcare burden. 3 marks
1.3 Anaphylaxis affects very few Australians per year yet still generates significant healthcare costs. Propose one reason, using your knowledge of anaphylaxis pathophysiology. 2 marks
2. Interpret graph — blood serum IgE levels across allergy states
The bar graph below shows median serum total IgE concentrations (IU/mL) in four groups: healthy non-allergic controls, mild hayfever, moderate persistent asthma (allergic), and anaphylaxis-risk patients (multiple food allergies). Data adapted from ASCIA clinical guidelines and Sporik et al. (1990). 6 marks
Adapted from Sporik et al. (1990) and ASCIA Clinical Immunology guidelines. Median values shown; error bars omitted for clarity.
2.1 Describe the trend in serum IgE levels from healthy controls to anaphylaxis-risk patients. Quote at least two figures. 2 marks
2.2 Using lesson content, explain why anaphylaxis-risk patients have much higher IgE levels than mild hayfever patients if both are Type I hypersensitivity reactions. 2 marks
2.3 A researcher proposes using serum IgE as a diagnostic marker for allergy severity. Identify one limitation of this approach based on the data and lesson content. 2 marks
3. Cause-and-effect chain — anaphylactic shock
The cause boxes are filled in. For each cause, write the immediate effect on the blank line to its right. Then complete the "overall outcome" statement at the bottom. 5 marks
| Cause | Effect (fill in) | |
|---|---|---|
| Allergen re-enters the body and cross-links IgE on mast cell surfaces throughout the body | → | |
| Massive, simultaneous histamine release from widespread mast cell degranulation | → | |
| Systemic vasodilation — blood pools in peripheral vessels | → | |
| Increased vascular permeability — plasma leaks into tissues, especially throat / tongue | → | |
| Severe bronchoconstriction — smooth muscle in bronchioles contracts | → |
Overall outcome (so…):
4. Australian case study — bee venom anaphylaxis management
In 2018, a study of emergency presentations to four Australian hospitals found that bee sting anaphylaxis was the leading cause of fatal anaphylaxis in adults in Australia, with 56% of fatal cases occurring in people who had experienced prior non-fatal reactions (Turner et al., 2017, J Allergy Clin Immunol). Venom immunotherapy (subcutaneous bee venom desensitisation) was available to only 37% of patients at risk. 6 marks
4.1 Explain, using the two-stage allergy mechanism, why prior non-fatal reactions predict severe future reactions. 2 marks
4.2 Describe the immunological mechanism by which venom immunotherapy (desensitisation) reduces the risk of anaphylaxis. 2 marks
4.3 Compare the mechanism of desensitisation to antihistamine therapy for managing bee venom allergy. Which is more likely to prevent a fatal anaphylaxis, and why? 2 marks
5. Compare autoimmune disease and Type I allergy
Complete the comparison table using information from Cards 1–5 of the lesson. 6 marks
| Feature | Autoimmune disease | Allergy (Type I hypersensitivity) |
|---|---|---|
| Immune target | ||
| Antibody class involved | ||
| Time course of symptoms | ||
| Key effector cell | ||
| Example treatment | ||
| Named Australian example |
Q1.1 — Prevalence vs cost pattern
Higher prevalence is not always associated with higher total cost. Allergic rhinitis (18% of Australians) costs only $0.9 billion annually, while Type 1 diabetes (0.5%) costs $2.1 billion — a much lower-prevalence condition costs more than twice as much in total. Anaphylaxis affects only ~0.02% per year but still generates $0.15 billion in costs, suggesting high per-episode cost. The data indicate that chronic, organ-destructive autoimmune conditions generate disproportionately high costs relative to their prevalence. [1 mark for identifying the non-linear relationship; 1 mark for citing at least two specific figures]
Q1.2 — Per-person cost difference
Allergic rhinitis is a Type I hypersensitivity in which IgE-mediated mast cell degranulation in nasal mucosa causes transient, localised histamine release. Symptoms are managed cheaply with over-the-counter antihistamines and nasal corticosteroids — neither is expensive and no organ is permanently destroyed. [1] Type 1 diabetes is an autoimmune disease in which cytotoxic T cells permanently destroy pancreatic beta cells, causing absolute insulin deficiency. Management requires lifelong insulin injections or pumps, continuous glucose monitoring, specialist endocrinology care, and treatment of vascular, renal and neuropathic complications. [1] The autoimmune disease causes irreversible organ destruction requiring lifelong intensive medical management, whereas the allergic condition causes reversible, episodic, locally contained symptoms. [1]
Q1.3 — Anaphylaxis cost vs low prevalence
Anaphylaxis is a medical emergency requiring immediate emergency department presentation, possible ICU admission, IV fluids, adrenaline infusions, and monitoring for biphasic reactions. The per-episode hospitalisation cost is very high — and even a small number of hospitalisations at high cost per episode generates a significant national total. Additionally, costs include EpiPen prescriptions, specialist allergy consultations and ambulance attendance. [1 per reasonable justification, max 2]
Q2.1 — IgE trend description
Serum IgE increases progressively from healthy controls (30 IU/mL) to mild hayfever (180 IU/mL) to moderate allergic asthma (420 IU/mL) to anaphylaxis-risk patients (850 IU/mL) — a roughly 28-fold increase from healthy to highest-risk group. [1 for trend direction; 1 for quoting two or more figures]
Q2.2 — Why anaphylaxis patients have higher IgE
Anaphylaxis-risk patients are sensitised to multiple allergens and have been re-exposed repeatedly, each time stimulating further IgE production by B cells against a wider range of antigens. Higher circulating IgE means more IgE bound to mast cells across the body — when any one allergen is encountered, more mast cells degranulate simultaneously, causing the systemic reaction. Mild hayfever involves IgE sensitisation to fewer antigens (e.g. a single pollen type) and the reaction remains localised to nasal mucosa. [1 per clear mechanism point; max 2]
Q2.3 — Limitation of using IgE as diagnostic marker
Total serum IgE measures the overall amount of IgE but not which allergen it is specific to — a person could have high IgE due to parasitic infection or eczema without being at risk of anaphylaxis. Additionally, some individuals with very high IgE have no clinical allergy, while rare cases of anaphylaxis can occur with lower IgE if the person is highly sensitive to a specific allergen. Allergen-specific IgE testing (RAST) or skin-prick testing is needed for clinical diagnosis, not total IgE alone. [1 for identifying the specificity problem; 1 for a valid example or consequence]
Q3 — Cause-and-effect chain answers
Row 1 effect: Widespread, simultaneous mast cell degranulation throughout the body (systemic degranulation).
Row 2 effect: Systemic vasodilation, increased vascular permeability, and bronchoconstriction — the combined inflammatory cascade of anaphylaxis begins.
Row 3 effect: Sudden drop in blood pressure (anaphylactic shock); organs are underperfused as blood pools in peripheral vessels.
Row 4 effect: Angioedema — swelling of face, tongue and throat; can obstruct the airway (upper airway compromise).
Row 5 effect: Respiratory distress / inability to breathe — wheeze, stridor, oxygen desaturation.
Overall outcome: Without rapid IM adrenaline administration and emergency medical care, anaphylaxis can progress to cardiovascular collapse and death within 5–10 minutes, particularly from airway obstruction and anaphylactic shock combined.
Q4.1 — Prior reactions predict future severity
Each bee sting exposure (assuming it does not kill) is an additional round of allergen re-exposure that may further stimulate B cells to produce more IgE specific to bee venom proteins. [1] As IgE levels increase and more mast cells are loaded with IgE, subsequent exposures cross-link more IgE molecules on more mast cells simultaneously, producing a more intense (potentially systemic) degranulation cascade — hence the risk of anaphylaxis increases with each non-fatal sting. [1]
Q4.2 — Mechanism of venom immunotherapy
Venom immunotherapy (desensitisation) administers escalating doses of bee venom subcutaneously over months to years. This gradually shifts the immune response from a Th2-driven IgE response toward a Th1/Treg response that produces IgG antibodies specific to venom proteins. [1] The IgG antibodies act as "blocking antibodies" that bind and neutralise the venom antigen before it can cross-link IgE on mast cells; simultaneously, reduced IgE production and increased T-reg activity lower mast cell sensitivity to the allergen. [1]
Q4.3 — Desensitisation vs antihistamine
Antihistamines block H1 histamine receptors on target cells but do not prevent mast cell degranulation — if anaphylaxis occurs, histamine is still released in full; antihistamines simply blunt one downstream effect and act too slowly to reverse the acute cardiovascular collapse. [1] Desensitisation actually modifies the underlying sensitisation by reducing IgE production and shifting to a Th1/IgG response, thereby reducing the probability that bee venom will trigger degranulation at all — a disease-modifying approach. Desensitisation is far more likely to prevent fatal anaphylaxis because it addresses the mechanism, not just one downstream mediator. [1]
Q5 — Compare-and-contrast table sample answers
Immune target: Autoimmune — self-antigens (body's own tissues); Allergy — non-self allergen (harmless foreign substance).
Antibody class: Autoimmune — IgG, IgM (or cytotoxic T cells); Allergy — IgE (bound to mast cells and basophils).
Time course: Autoimmune — chronic, progressive over months to years; Allergy — immediate (minutes after re-exposure to allergen).
Key effector cell: Autoimmune — cytotoxic T cells or antibody-producing B cells (IgG/IgM); Allergy — mast cells and basophils (IgE-loaded).
Example treatment: Autoimmune — immunosuppressants (prednisolone), DMARDs (methotrexate), biologics (adalimumab); Allergy — antihistamines, adrenaline (anaphylaxis), desensitisation.
Named Australian example: Autoimmune — multiple sclerosis (Australia has one of the world's highest MS prevalence rates); Allergy — bee venom anaphylaxis / peanut allergy / hayfever due to introduced grasses (e.g. rye grass pollen).