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PA8.1-6,PA9.1-2 | Immunopathology & Amyloidosis — PBL Case

CLINICAL SETTING

Ravi, a 12-year-old boy from a small town in Rajasthan, is brought to the district hospital emergency by his father after collapsing at a school lunch function. His father reports that within minutes of eating groundnut chutney, Ravi's face swelled up dramatically, he broke out in generalised hives, began wheezing, and then lost consciousness. This is the second such episode in six months — the first ended in a brief loss of consciousness but resolved spontaneously before medical care was reached. Today, Ravi's blood pressure is 60/40 mmHg and he is barely responsive. The treating doctor stabilises Ravi with a single intramuscular injection and supportive measures. Within 20 minutes, he is awake, asking for water. Once out of immediate danger, the family mentions something else: Ravi's maternal grandmother and a maternal uncle both have 'kidney problems,' and a cousin in Jodhpur has recently been diagnosed with a condition the family vaguely recalls as involving 'deposits in multiple organs.'

Trigger 1: Collapse at Lunch

Ravi is brought in unconscious. Pulse: 140/min, thready. BP: 60/40 mmHg. Respiratory rate: 32/min with audible wheeze. Face shows angioedema of lips and periorbital tissues. Generalised urticaria covers trunk and limbs. The school nurse who was present at the event says Ravi ate groundnut chutney at exactly 12:47 PM and collapsed at 12:54 PM.

DISCUSSION POINTS

  • What arm of the immune system is responsible for this reaction, and what is the precise molecular sequence from antigen exposure to the collapse Ravi is experiencing?
  • Mast cells and basophils both carry IgE on their surface — what distinguishes the contribution of each in the systemic versus local manifestations seen in this case?
  • The treating doctor reaches for a single drug and gives it intramuscularly. What is this drug, and why is this specific route, site, and dose critical in this life-threatening situation?
  • If Ravi had never been exposed to groundnut protein before today, could this reaction have occurred? Explain the concept of prior sensitisation in the context of his history.
Click to reveal Trigger 2: Allergy Workup and a Family Secret (discuss previous trigger first!)

Trigger 2: Allergy Workup and a Family Secret

Ravi is admitted for observation. Serum total IgE is 1,840 IU/mL (normal <100). Skin prick testing three weeks later confirms sensitivity to Arachis hypogaea (groundnut) with a 12 mm wheal. During allergy clinic, the family history emerges more clearly: Ravi's maternal grandmother died of 'kidney failure with swelling all over.' His uncle, 45 years old, has had recurrent febrile illness since childhood, with progressively enlarging spleen and now stage 3 chronic kidney disease. A biopsy report from the uncle (brought along by the family) mentions 'amorphous eosinophilic deposits in glomeruli, staining positive with Congo red, showing apple-green birefringence under polarised light.'

DISCUSSION POINTS

  • The biopsy report describes a specific substance depositing in the uncle's kidneys. What class of structural protein is this, and what key biochemical feature allows it to form these characteristic deposits?
  • Classify the type of amyloidosis the uncle most likely has, and identify the precursor protein — given the combination of recurrent febrile illness since childhood, splenomegaly, and progressive renal involvement.
  • Ravi's grandmother may have had the same condition. Draw a mechanistic pathway from the uncle's recurrent infections to his current kidney disease, naming the intermediate proteins involved.
  • What organs are most commonly affected by the type of amyloidosis you have identified? Which organ is characteristically spared, and why is this clinically relevant in this family?
Click to reveal Trigger 3: Long-Term Management and a New Diagnosis (discuss previous trigger first!)

Trigger 3: Long-Term Management and a New Diagnosis

Ravi is referred to an immunology clinic in Jaipur for allergen-specific immunotherapy assessment. While there, a detailed immunological workup for the family is initiated. The uncle's workup reveals: serum amyloid A (SAA) persistently elevated at 320 mg/L (normal <10). A fat pad aspirate shows apple-green birefringence. Renal biopsy demonstrates mesangial and subendothelial deposits obliterating glomerular architecture; electron microscopy shows non-branching fibrils of 7–10 nm diameter. The treating physician explains there is no curative treatment but discusses strategies to slow progression. Ravi's own immunology workup, done for screening, reveals no evidence of amyloidosis, but his IgE-mediated hypersensitivity is confirmed. He is enrolled in a structured programme and given a device to carry at all times.

DISCUSSION POINTS

  • The uncle's electron microscopy shows 7–10 nm non-branching fibrils. What molecular configuration do these fibrils adopt, and how does this structure explain their resistance to proteolytic degradation and their Congo red staining property?
  • Ravi has been given a device to carry at all times. What is this device, and outline a structured plan — at the level of a district hospital — for his long-term management including allergen avoidance, emergency response, and family education?
  • Compare the immunological mechanisms of Type I, Type II, Type III, and Type IV hypersensitivity using Ravi and his uncle's case as anchors — identifying one real or potential example from this family narrative for each type.
  • If the uncle had a solid organ transplant, which arm of the immune system would be primarily responsible for graft rejection? How would this differ from the immune mechanism that nearly killed Ravi today?

Group Task Assignments

Group 1: Mechanisms of Type I hypersensitivity and anaphylaxis

  • Draw a stepwise diagram of the sensitisation and effector phases of IgE-mediated hypersensitivity, identifying the cellular players, key mediators, and their end-organ effects.
  • Prepare a 5-minute presentation for a PHC-level health worker explaining how to recognise anaphylaxis and what first aid steps to take before reaching hospital.

Competencies: PA8.1, PA8.2

Group 2: Amyloidosis — types, pathogenesis and morphology

  • Construct a table comparing primary (AL), secondary (AA), and familial amyloidosis: precursor protein, associated condition, organs affected, and diagnostic markers.
  • Describe the gross and microscopic morphology of amyloidosis in the kidney, including the Congo red staining result and its significance in clinical practice.

Competencies: PA9.1, PA9.2

Group 3: Autoimmunity and the HLA system

  • Explain the concept of self-tolerance and how its failure leads to autoimmune disease. Use at least two mechanisms (molecular mimicry, bystander activation) with specific disease examples.
  • Summarise the HLA system's role in transplant matching and the three types of graft rejection, correlating each with its underlying immune mechanism.

Competencies: PA8.3, PA8.4

Group 4: HIV/AIDS pathogenesis and immunodeficiency

  • Outline the molecular steps of HIV entry into CD4+ T cells and explain why loss of these cells leads to the specific pattern of opportunistic infections seen at different CD4 count thresholds.
  • Prepare a case scenario of a patient presenting to a district hospital with a CD4 count of 80/mm³ — list the likely opportunistic infections, the investigations a district hospital can perform, and the initial management steps available at that level.

Competencies: PA8.5, PA8.6

Group 5: SLE pathogenesis and clinical-pathological correlation

  • Map the pathogenesis of SLE from failed apoptotic debris clearance to multi-organ damage, identifying the key autoantibodies and the tissues each damages.
  • List the SOAP BRAIN MD criteria for SLE diagnosis and correlate each clinical feature with its underlying immunopathological mechanism.

Competencies: PA8.4, PA8.5

Learning Issues

Research these questions and bring your findings to the discussion.

  1. [PA8.1] What are the mechanisms of innate and adaptive immunity, and how do they interact to mount and regulate an immune response?
  2. [PA8.2] What are the four types of hypersensitivity reactions, and what are the specific mediators, time course, and tissue effects of each type?
  3. [PA8.3] What is the HLA system, how does it relate to immune surveillance and disease susceptibility, and what are the mechanisms of hyperacute, acute, and chronic transplant rejection?
  4. [PA8.4] How does failure of self-tolerance lead to autoimmunity, and what are the pathological mechanisms underlying common organ-specific and systemic autoimmune diseases?
  5. [PA8.5] What is the pathogenesis of SLE, what autoantibodies drive multi-organ damage, and how are the clinical features correlated with underlying immunopathology?
  6. [PA8.6] How does HIV enter and destroy CD4+ T lymphocytes, what is the natural history of HIV infection, and how do opportunistic infections correlate with falling CD4 counts?
  7. [PA9.1] What is the pathogenesis of amyloidosis — how are amyloid fibrils formed, why are they resistant to degradation, and what are the differences between major types of systemic amyloidosis?
  8. [PA9.2] What are the gross and microscopic features of amyloidosis in different organs, and what staining and imaging techniques are used to identify and characterise amyloid deposits?