Immunopathology Practice Questions

Q: Memory T cells can be identified by using which of the following markers?

CD45RO. **Explanation:** The correct answer is **CD45RO**. **1. Why CD45RO is correct:** CD45 (also known as Leukocyte Common Antigen) is a transmembrane protein tyrosine phosphatase essential for T-cell activation. It exists in several isoforms due to alternative splicing of exons 4, 5, and 6 (A, B, and C). * **CD45RO** is the shortest isoform (lacking exons A, B, and C). It is specifically expressed on **Memory T cells** [1] and activated effector T cells. Its structure allows for more efficient interaction with the T-cell receptor (TCR) complex, facilitating a rapid secondary immune response upon re-exposure to an antigen. **2. Why the other options are incorrect:** * **CD45RA:** This isoform contains the 'A' exon. It is the classic marker for **Naive T cells** (T cells that have not yet encountered their specific antigen) [1]. * **CD45RB and CD45RC:** These isoforms are typically expressed on naive B cells, subsets of T cells, and other myeloid cells. They are not specific markers used to differentiate memory T cells in a clinical or examination context. **3. NEET-PG High-Yield Pearls:** * **The Switch:** When a Naive T cell (CD45RA+) encounters an antigen, it undergoes activation and "switches" its expression to the memory phenotype (**CD45RO+**). * **CD4 vs. CD8:** Both Helper (CD4+) and Cytotoxic (CD8+) T cells can be subdivided into Naive and Memory subsets using these markers. * **Clinical Correlation:** In certain immunodeficiencies or lymphomas, the ratio of CD45RA to CD45RO can be diagnostically significant. * **Mnemonic:** "R**O**" for **O**ld (Memory) cells; "R**A**" for **A**mateur (Naive) cells. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 198.

Q: What is the normal CD4:CD8 ratio?

2:1. **Explanation:** In a healthy individual, the normal **CD4:CD8 ratio is approximately 2:1** [1]. This ratio represents the balance between T-helper cells (CD4+), which orchestrate the immune response, and T-cytotoxic cells (CD8+), which directly kill infected or malignant cells. In peripheral blood, CD4+ T cells typically make up about 60–70% of the T-cell population, while CD8+ T cells account for about 30%. **Analysis of Options:** * **Option B (2:1):** This is the physiological baseline [1]. Maintaining this ratio is crucial for effective immune surveillance without excessive immunosuppression or autoimmunity. * **Option A (3:1):** While some healthy individuals may have a slightly higher ratio, 2:1 is the standard clinical benchmark used in pathology and immunology. * **Options C & D (1:2 and 1:3):** These represent an **inverted ratio**. A ratio of less than 1:1 is clinically significant and pathological, indicating either a depletion of CD4 cells or an expansion of CD8 cells [1]. **Clinical Pearls for NEET-PG:** 1. **HIV/AIDS:** The hallmark of HIV progression is the progressive destruction of CD4+ T cells, leading to an **inverted CD4:CD8 ratio** (often <0.5) [1]. Monitoring this ratio is vital for staging the disease. 2. **Other Causes of Inversion:** Apart from HIV, an inverted ratio can be seen in viral infections (EBV, CMV), aging, chronic inflammation, and certain primary immunodeficiencies. 3. **Sarcoidosis:** A high-yield contrast is that in Sarcoidosis, the CD4:CD8 ratio in **Bronchoalveolar Lavage (BAL) fluid** is typically significantly **increased (>3.5:1)**, aiding in diagnosis. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Diseases Of The Urinary And Male Genital Tracts, pp. 555-556.

Question 1

X-linked agammaglobulinemia should be suspected if:

Accepted Answer

Absent tonsils and no palpable lymph nodes on physical examination

Answer

Female sex

Answer

High isohemagglutinin titers

Answer

Low CD3 count

Question 2

Which of the following is a Type 2 Hypersensitivity reaction?

Accepted Answer

Autoimmune Hemolytic anaemia

Answer

Chronic Kidney Rejection episode

Answer

Arthus reaction

Answer

Mitsuda reaction

Question 3

Memory T cells can be identified by using which of the following markers?

Accepted Answer

CD45RO

Answer

CD45RA

Answer

CD45RB

Answer

CD45RC

Question 4

Class I MHC molecules are expressed on all of the following cell types EXCEPT:

Accepted Answer

Red blood cells

Answer

Dendritic cells

Answer

Epithelial cells

Answer

Platelets

Question 5

A 35-year-old woman with end-stage renal disease of unknown etiology is transplanted with a cadaver kidney. The patient develops oliguria shortly after transplantation and a renal biopsy shows immediate (hyperacute) rejection. Immunosuppression improves renal function. Which of the following represents the principle target for immune attack directed against this patient's allograft?

Accepted Answer

ABO antigens

Answer

Bacterial antigens

Answer

Glomerular basement membrane antigens

Answer

b2-Microglobulin

Question 6

A 35-year-old man presents with hemoptysis. He has no history suggestive of tuberculosis exposure, and his chest x-ray does not show a mass lesion. Serial chest x-rays reveal asymmetric densities in both lungs that change in shape and position. Urinalysis shows hematuria, proteinuria, and cellular and granular casts. Renal biopsy demonstrates rapidly progressive glomerulonephritis with prominent epithelial cell crescents. The mechanism causing this patient's disease is most closely related to the mechanism underlying which of the following diseases?

Accepted Answer

Bullous pemphigoid

Answer

Graves disease

Answer

Hereditary angioedema

Answer

Rheumatoid arthritis

Question 7

What is the most potent stimulator of naive T-cells?

Accepted Answer

Mature dendritic cells

Answer

Follicular dendritic cells

Answer

Macrophages

Answer

B-cells

Question 8

What is the normal CD4:CD8 ratio?

Accepted Answer

2:1

Answer

3:1

Answer

1:2

Answer

1:3

Question 9

Which of the following statements best characterizes natural killer cells?

Accepted Answer

They participate in antibody-dependent cellular cytotoxicity reactions.

Answer

They are a subset of T cells.

Answer

They are involved in type III hypersensitivity reactions.

Answer

They require prior sensitization in order to kill virally infected cells or tumor cells.

Question 10

Amyloid is detected by staining with which of the following, except?

Accepted Answer

Alcain Blue

Answer

Methyl violet

Answer

Congo Red

Answer

Thioflavin

Immunopathology — MCQs

Immunopathology — MCQs

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