Immunopathology Practice Questions

Q: A 6-year-old boy presents with recurrent sinopulmonary infections since age 2. He has had three episodes of pneumococcal pneumonia and two episodes of H. influenzae meningitis despite appropriate vaccinations. Serum studies show low IgG (200 mg/dL), low IgA (10 mg/dL), and low IgM (15 mg/dL). Flow cytometry shows absent CD19+ B cells but normal CD3+ T cells. Apply this immunologic profile to determine the underlying defect.

Defective tyrosine kinase preventing B cell maturation. ***Defective tyrosine kinase preventing B cell maturation*** - This patient has **X-linked agammaglobulinemia (Bruton's)**, characterized by a mutation in **Bruton Tyrosine Kinase (BTK)**, which prevents **pre-B cells** from maturing into mature **B cells (CD19+)**. - The clinical presentation of recurrent infections with **encapsulated organisms** (Pneumococcus, H. influenzae) and **pan-hypogammaglobulinemia** typically manifests after **maternal IgG** wanes (around 6 months of age). *Defective NADPH oxidase in phagocytes* - This is the underlying defect in **Chronic Granulomatous Disease (CGD)**, which leads to impaired killing of **catalase-positive organisms** (e.g., S. aureus, Aspergillus). - Patients with CGD have normal levels of B and T cells and do not present with the global **hypogammaglobulinemia** seen in this case. *Absent CD40 ligand on activated T cells* - This defect causes **Hyper-IgM Syndrome**, where B cells cannot undergo **class-switching**, leading to high or normal IgM but absent IgG, IgA, and IgE. - Unlike the patient in the scenario, flow cytometry would show a **normal number of CD19+ B cells**, though they are functionally immature. *Absent thymic shadow with T cell lymphopenia* - An **absent thymic shadow** is characteristic of **DiGeorge Syndrome** (22q11 deletion) or **SCID**, both of which involve profound **T-cell (CD3+) deficiency**. - This patient has a **normal CD3+ T cell count**, which rules out primary thymic or pan-lymphocyte aplasia. *Defective adenosine deaminase causing lymphocyte toxicity* - This describes **Adenosine Deaminase (ADA) deficiency**, a common cause of **Autosomal Recessive SCID**. - This condition leads to the accumulation of **toxic metabolites** that kill both **B cells and T cells**, whereas this patient has preserved T-cell numbers.

Q: A 28-year-old woman presents with a butterfly rash, photosensitivity, and joint pain for 3 months. Laboratory studies show positive ANA (1:640), anti-dsDNA antibodies, and decreased C3 and C4 complement levels. Urinalysis reveals proteinuria (3+) and RBC casts. Apply your understanding of immune complex-mediated disease to determine the primary pathologic mechanism.

Type III hypersensitivity with immune complex deposition. ***Type III hypersensitivity with immune complex deposition*** - Systemic Lupus Erythematosus (SLE) involves the formation of **circulating antigen-antibody complexes** that deposit in tissues like the **renal glomeruli**, leading to glomerulonephritis. - Deposition triggers the **complement cascade**, resulting in decreased **C3 and C4 levels** and the recruitment of neutrophils that cause tissue damage. *Type I hypersensitivity with IgE-mediated mast cell degranulation* - This mechanism is associated with **atopic reactions** like asthma, hay fever, and anaphylaxis involving **IgE antibodies**. - It does not explain the formation of **anti-dsDNA antibodies** or the presence of **RBC casts** and proteinuria seen in this patient. *Type IV hypersensitivity with delayed T-cell mediated response* - This is a cell-mediated response involving **sensitized T-lymphocytes**, which is characteristic of conditions like the **tuberculin skin test** or contact dermatitis. - While T-cells play a role in the pathogenesis of SLE, the acute presentation of **malar rash** and **lupus nephritis** is primarily driven by immune complex deposition. *Type II hypersensitivity with antibody-mediated cytotoxicity* - While SLE can have Type II components (e.g., **autoimmune hemolytic anemia**), it involves antibodies binding directly to **cell-surface antigens**. - The systemic features and renal involvement with **low complement** are hallmark indicators of **Type III** rather than Type II hypersensitivity. *Type V hypersensitivity with antibody-mediated receptor stimulation* - This involves antibodies that mimic or block **hormone-receptor** activity, such as in **Graves' disease** or **Myasthenia Gravis**. - It is not a mechanism for multi-system inflammatory damage or **glomerular injury** characterized by proteinuria and casts.

Question 1

A 6-year-old boy presents with recurrent sinopulmonary infections since age 2. He has had three episodes of pneumococcal pneumonia and two episodes of H. influenzae meningitis despite appropriate vaccinations. Serum studies show low IgG (200 mg/dL), low IgA (10 mg/dL), and low IgM (15 mg/dL). Flow cytometry shows absent CD19+ B cells but normal CD3+ T cells. Apply this immunologic profile to determine the underlying defect.

Accepted Answer

Defective tyrosine kinase preventing B cell maturation

Answer

Defective NADPH oxidase in phagocytes

Answer

Absent CD40 ligand on activated T cells

Answer

Absent thymic shadow with T cell lymphopenia

Answer

Defective adenosine deaminase causing lymphocyte toxicity

Question 2

A 45-year-old man with rheumatoid arthritis on methotrexate develops progressive dyspnea and dry cough. Chest CT shows bilateral ground-glass opacities. Bronchoalveolar lavage reveals CD8+ T lymphocytes. Transbronchial biopsy shows non-caseating granulomas with multinucleated giant cells. Apply immunologic principles to identify the hypersensitivity reaction causing his pulmonary symptoms.

Accepted Answer

Type IV hypersensitivity from drug-induced delayed T-cell response

Answer

Type III hypersensitivity from methotrexate-protein immune complexes

Answer

Type I hypersensitivity from methotrexate-induced IgE production

Answer

Type II hypersensitivity from anti-basement membrane antibodies

Answer

Mixed Type II and III hypersensitivity with complement activation

Question 3

A 28-year-old woman presents with a butterfly rash, photosensitivity, and joint pain for 3 months. Laboratory studies show positive ANA (1:640), anti-dsDNA antibodies, and decreased C3 and C4 complement levels. Urinalysis reveals proteinuria (3+) and RBC casts. Apply your understanding of immune complex-mediated disease to determine the primary pathologic mechanism.

Accepted Answer

Type III hypersensitivity with immune complex deposition

Answer

Type I hypersensitivity with IgE-mediated mast cell degranulation

Answer

Type IV hypersensitivity with delayed T-cell mediated response

Answer

Type II hypersensitivity with antibody-mediated cytotoxicity

Answer

Type V hypersensitivity with antibody-mediated receptor stimulation

Immunopathology — MCQs

Immunopathology — MCQs

On this page

Practice by Chapter

Want unlimited practice?