Immunopathology Practice Questions

Q: A 6-year-old boy presented with recurrent pyogenic abscess, runny nose, oral thrush, and rash on perineal areas. Pus culture showed growth of Staphylococcus aureus. A test was performed whose finding is shown below. What is the most common mode of inheritance of this disorder?

X-linked recessive. ***X-linked recessive*** - The clinical presentation of recurrent **pyogenic abscesses** and **Staphylococcus aureus** infections in a young boy strongly suggests **Chronic Granulomatous Disease (CGD)**, with X-linked inheritance being the most common form (65-70% of cases). - X-linked CGD is caused by mutations in the **gp91phox gene (CYBB)** on the X chromosome, explaining why males are predominantly affected with this severe phenotype. *Autosomal recessive* - While autosomal recessive forms of CGD do exist (accounting for 30-35% of cases), they are **less common** than X-linked inheritance. - Autosomal recessive CGD involves mutations in genes like **p22phox**, **p47phox**, or **p67phox**, but X-linked remains the predominant inheritance pattern. *Autosomal dominant* - CGD does not typically follow an **autosomal dominant** inheritance pattern as it requires complete loss of **NADPH oxidase function**. - Heterozygous carriers usually have sufficient enzyme activity to prevent the severe immunodeficiency seen in this patient. *Mitochondrial inheritance* - **Mitochondrial inheritance** affects both males and females equally and is passed through the maternal line. - CGD specifically involves defects in the **NADPH oxidase complex** located in phagocytic cell membranes, not mitochondrial dysfunction.

Q: All of the following are true regarding Bruton's Agammaglobulinemia except:

It is X-linked.. **Explanation:** Bruton’s Agammaglobulinemia, also known as **X-linked Agammaglobulinemia (XLA)**, is a primary immunodeficiency caused by a mutation in the **BTK (Bruton Tyrosine Kinase) gene**. This kinase is essential for the maturation of Pre-B cells into mature B cells. **Why Option D is the correct answer (the "Except" statement):** In XLA, there is a complete failure of B-cell maturation. Consequently, there are **virtually no mature B cells** in the peripheral blood and a **marked absence of plasma cells** in lymphoid tissues. Since plasma cells are responsible for antibody production, all classes of immunoglobulins (IgG, IgA, IgM, IgE, IgD) are severely depleted. **Analysis of other options:** * **Option A & C:** XLA follows an **X-linked recessive** inheritance pattern. Therefore, it is typically seen **only in males**, while females act as asymptomatic carriers. * **Option B:** This is a pure B-cell defect. **T-cell numbers and functions remain normal**, which is a key diagnostic feature used to differentiate it from Combined Immunodeficiencies (like SCID). **NEET-PG High-Yield Pearls:** * **Clinical Presentation:** Recurrent pyogenic infections (e.g., *S. pneumoniae*, *H. influenzae*) starting after 6 months of age (once maternal IgG wanes). * **Physical Exam:** Characterized by **absent or hypoplastic tonsils** and lymph nodes. * **Diagnosis:** Flow cytometry shows absent CD19+ B cells; Quantitative PCR confirms BTK gene mutation. * **Treatment:** Lifelong Intravenous Immunoglobulin (IVIG) replacement; Live vaccines are strictly contraindicated.

Question 1

Antibody-dependent cell-mediated cytotoxicity (ADCC) is a mechanism by which target cells are killed. Which immune cells are primarily involved in ADCC?

Accepted Answer

NK cells, neutrophils, and macrophages

Answer

NK cells

Answer

NK cells only

Answer

Macrophages

Question 2

Which type of cell mediates the immunological reaction against a transplanted organ?

Accepted Answer

T-cells

Answer

B-cells

Answer

NK cells

Answer

Granulocytes

Question 3

Which CD molecule is important for the presentation of lipid antigens?

Accepted Answer

CD1

Answer

CD4

Answer

CD8

Answer

CD16

Question 4

All are true regarding agammaglobulinemia except:

Accepted Answer

Decreased red pulp in spleen

Answer

Loss of germinal center in lymph node

Answer

Normal cortical lymphocytes

Answer

Normal cortical lymphocytes in paracortex and medulla

Question 5

A 6-year-old boy presented with recurrent pyogenic abscess, runny nose, oral thrush, and rash on perineal areas. Pus culture showed growth of Staphylococcus aureus. A test was performed whose finding is shown below. What is the most common mode of inheritance of this disorder?

Accepted Answer

X-linked recessive

Answer

Autosomal recessive

Answer

Autosomal dominant

Answer

Mitochondrial inheritance

Question 6

Which immunoglobulin (Ig) is primarily active in Type 1 hypersensitivity reactions?

Accepted Answer

IgE

Answer

IgA

Answer

IgD

Answer

IgG

Question 7

All of the following are true regarding Bruton's Agammaglobulinemia except:

Accepted Answer

It is X-linked.

Answer

T cell abnormality is seen.

Answer

It is seen only in males.

Answer

There is an increase in the number of plasma cells.

Question 8

A 10-year-old boy with a history of recurrent bacterial infections presents with fever and a productive cough. Biochemical analysis of his neutrophils demonstrates defective oxidative burst. This patient most likely has inherited mutations in the gene that encodes which of the following proteins?

Accepted Answer

NADPH oxidase

Answer

Catalase

Answer

Cytochrome P450

Answer

Myeloperoxidase

Question 9

Which is the most important Human Leukocyte Antigen (HLA) locus for organ transplantation and tissue typing?

Accepted Answer

HLA-D

Answer

HLA-A

Answer

HLA-B

Answer

HLA-C

Question 10

All of the following autoimmune disorders are more common in females, except:

Accepted Answer

Type I diabetes

Answer

Idiopathic Thrombocytopenic Purpura (ITP)

Answer

Multiple sclerosis

Answer

Scleroderma

Immunopathology — MCQs

Immunopathology — MCQs

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