Immunopathology Practice Questions

Q: Thymic hypoplasia is seen in which of the following conditions?

All of the above. **Explanation:** The correct answer is **D. All of the above**. Thymic hypoplasia refers to the underdevelopment of the thymus, leading to impaired T-cell maturation and cell-mediated immunity. 1. **DiGeorge Syndrome (Option A):** This is the classic cause of thymic hypoplasia. It results from a microdeletion on chromosome **22q11**, leading to the failure of the **3rd and 4th pharyngeal pouches** to develop. This manifests as the CATCH-22 mnemonic: Cardiac defects, Abnormal facies, **Thymic hypoplasia**, Cleft palate, and Hypocalcemia (due to parathyroid hypoplasia). 2. **Ataxia Telangiectasia (Option C):** This is an autosomal recessive DNA repair defect (ATM gene). While primarily known for cerebellar ataxia and oculocutaneous telangiectasia, it also involves **thymic hypoplasia/dysplasia**, leading to combined immunodeficiency and an increased risk of malignancies. 3. **Common Variable Immunodeficiency (CVID) (Option B):** While CVID is primarily characterized by hypogammaglobulinemia (B-cell defect), a significant subset of patients (up to 20-30%) exhibit T-cell abnormalities, including reduced thymic output and functional thymic impairment, which can manifest as varying degrees of thymic atrophy or hypoplasia. **NEET-PG High-Yield Pearls:** * **Chest X-ray finding:** The absence of a "Thymic Shadow" in a neonate is a classic sign of DiGeorge Syndrome or SCID. * **Nezelof Syndrome:** An autosomal recessive condition characterized by thymic hypoplasia with normal or near-normal immunoglobulin levels. * **SCID (Severe Combined Immunodeficiency):** Also presents with a vestigial/hypoplastic thymus, but is not listed as a standalone option here. * **Hassall’s Corpuscles:** These are characteristically absent or reduced in cases of thymic dysplasia/hypoplasia.

Q: SS-A (Ro) and SS-B (La) antibodies found in Sjogren syndrome are targeted against which cellular component?

Ribonucleoproteins. **Explanation:** The correct answer is **Ribonucleoproteins**. SS-A (Ro) and SS-B (La) are autoantibodies directed against small cytoplasmic **ribonucleoproteins (RNPs)** [1]. These proteins are complexed with small RNA molecules (Y1-Y5 RNA) and play roles in RNA processing and translation. * **SS-A (Ro):** Targets 52 kDa or 60 kDa proteins. It is the most common antibody in Sjogren Syndrome (70-90%) but is also found in Systemic Lupus Erythematosus (SLE) [1]. * **SS-B (La):** Targets a 48 kDa protein. It is highly specific for Sjogren Syndrome when found in conjunction with SS-A [1]. **Analysis of Incorrect Options:** * **A. DNA topoisomerase 1:** This is the target for **Anti-Scl-70** antibodies, which are highly specific for **Diffuse Cutaneous Systemic Sclerosis**. * **B. Histones:** Anti-histone antibodies are the hallmark of **Drug-Induced Lupus Erythematosus (DILE)**. * **D. Native DNA:** Also known as double-stranded DNA (dsDNA), these are the target for **Anti-dsDNA** antibodies, which are highly specific for **SLE** and correlate with renal involvement (lupus nephritis). **High-Yield Clinical Pearls for NEET-PG:** * **Neonatal Lupus:** Maternal SS-A (Ro) and SS-B (La) antibodies can cross the placenta, leading to neonatal lupus, characterized by **congenital heart block** and photosensitive rash. * **Diagnosis:** Sjogren syndrome is characterized by the triad of xerophthalmia (dry eyes), xerostomia (dry mouth), and parotid gland swelling [1]. * **Schirmer’s Test:** Used to quantify decreased lacrimal gland secretion (<5mm in 5 mins is positive). * **Malignancy Risk:** Patients with Sjogren Syndrome have a 40-fold increased risk of developing **B-cell MALT Lymphoma**.

Q: Which of the following is a type III hypersensitivity reaction?

Arthus reaction. ### Explanation **Type III Hypersensitivity** is an **immune-complex-mediated** reaction. It occurs when soluble antigen-antibody (IgG or IgM) complexes are not adequately cleared by the reticuloendothelial system, leading to their deposition in tissues (like blood vessel walls, synovial membrane, or glomerular basement membrane). This triggers the classical complement pathway, attracting neutrophils that release lysosomal enzymes, causing tissue damage and vasculitis. **Why Option C is Correct:** The **Arthus reaction** is the classic localized example of Type III hypersensitivity. It occurs when an antigen is injected intradermally into an individual who already has high levels of circulating IgG antibodies. The resulting local immune complexes deposit in small dermal blood vessels, causing edema, hemorrhage, and necrosis. **Analysis of Incorrect Options:** * **A. Prausnitz-Kustner (PK) reaction:** This is a classic test for **Type I (Immediate) Hypersensitivity**. It involves the passive transfer of IgE antibodies via serum from an allergic individual to a non-allergic one. * **B. Contact dermatitis:** This is a **Type IV (Delayed-type) Hypersensitivity** reaction mediated by T-cells (specifically Th1 and CD8+ cells), not antibodies. * **D. Rh incompatibility:** This is a **Type II (Cytotoxic) Hypersensitivity** reaction where antibodies (IgG) target antigens on the surface of red blood cells, leading to their destruction. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Hypersensitivity (ACID):** **A**naphlyactic (I), **C**ytotoxic (II), **I**mmune-Complex (III), **D**elayed (IV). * **Systemic Type III examples:** Serum sickness, Systemic Lupus Erythematosus (SLE), Post-streptococcal glomerulonephritis (PSGN), and Rheumatoid Arthritis. * **Key Mediator:** Complement components **C3a, C4a, and C5a** (anaphylatoxins) are crucial in Type III reactions for recruiting neutrophils.

Q: A 5-year-old boy presented with pyogenic abscess, runny nose, oral thrush & rash on perineal areas. On culturing pus Staphylococcus aureus was isolated. A test was performed whose finding is shown below. Which of the following is the most likely gene involved in the above condition?

LYST. ***LYST*** - **Chediak-Higashi syndrome** is caused by mutations in the **LYST gene**, presenting with recurrent **bacterial and fungal infections**, including **Staphylococcus aureus** abscesses as seen in this case. - The characteristic finding is **giant azurophilic granules** in **neutrophils and other leukocytes** on peripheral blood smear, which impairs their bactericidal function. *PHOX2B* - This gene is associated with **congenital central hypoventilation syndrome** (Ondine's curse), affecting respiratory control centers in the brainstem. - It does not cause **immunodeficiency** or predispose to **recurrent infections** with characteristic granule abnormalities. *MYC* - **MYC** is an **oncogene** involved in cell proliferation and is associated with various **malignancies** like Burkitt lymphoma. - It does not cause **primary immunodeficiency** or the specific **granule abnormalities** seen in this patient's blood smear. *RAS* - **RAS** is an **oncogene** involved in cell signaling pathways and is associated with **cancer development** when mutated. - It does not cause **immunodeficiency syndromes** or the characteristic **giant granules** in leukocytes observed in this case.

Question 1

Thymic hypoplasia is seen in which of the following conditions?

Accepted Answer

All of the above

Answer

DiGeorge syndrome

Answer

Common variable immunodeficiency

Answer

Ataxia telangiectasia

Question 2

Which type of hypersensitivity reaction is Rh incompatibility?

Accepted Answer

Type 2 hypersensitivity reaction

Answer

Type 1 hypersensitivity reaction

Answer

Type 3 hypersensitivity reaction

Answer

Type 4 hypersensitivity reaction

Question 3

Human leukocyte antigen (HLA), which plays an important role in graft rejection, is present on which chromosome?

Accepted Answer

Short arm of chromosome 6

Answer

Long arm of chromosome 6

Answer

Short arm of chromosome 3

Answer

Long arm of chromosome 3

Question 4

SS-A (Ro) and SS-B (La) antibodies found in Sjogren syndrome are targeted against which cellular component?

Accepted Answer

Ribonucleoproteins

Answer

DNA topoisomerase 1

Answer

Histones

Answer

Native DNA

Question 5

All of the following are neoplasms found in patients with HIV infection EXCEPT?

Accepted Answer

Hepatocellular carcinoma

Answer

Kaposi sarcoma

Answer

Primary lymphoma of brain

Answer

Invasive cancer of uterine cervix

Question 6

Which pair of organs is involved in Goodpasture's syndrome?

Accepted Answer

Kidney and lungs

Answer

Kidney and intestine

Answer

Kidney and heart

Answer

Kidney and liver

Question 7

Sago spleen is seen in which condition?

Accepted Answer

Amyloidosis

Answer

Infarction

Answer

Chronic venous congestion

Answer

Tuberculosis

Question 8

Granuloma formation is seen in which type of hypersensitivity reaction?

Accepted Answer

Type IV

Answer

Type I

Answer

Type II

Answer

Type III

Question 9

Which of the following is a type III hypersensitivity reaction?

Accepted Answer

Arthus reaction

Answer

Prausnitz-kustner reaction

Answer

Contact dermatitis

Answer

Rh incompatibility

Question 10

A 5-year-old boy presented with pyogenic abscess, runny nose, oral thrush & rash on perineal areas. On culturing pus Staphylococcus aureus was isolated. A test was performed whose finding is shown below. Which of the following is the most likely gene involved in the above condition?

Accepted Answer

LYST

Answer

PHOX2B

Answer

MYC

Answer

RAS

Immunopathology — MCQs

Immunopathology — MCQs

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