Immunopathology Practice Questions

Q: Which of the following is a pan-T lymphocyte marker?

CD3. **Explanation:** **CD3** is considered the definitive **pan-T lymphocyte marker** because it is physically associated with the T-cell receptor (TCR) [1]. It is required for the cell-surface expression of the TCR and is involved in the signal transduction pathway following antigen recognition [1]. It is expressed on all mature T-cells (both Helper T-cells and Cytotoxic T-cells) and is the most reliable marker used in immunohistochemistry to identify T-cell lineages [2]. **Analysis of Incorrect Options:** * **CD2:** While CD2 is an early marker found on T-cells and Natural Killer (NK) cells, it is primarily an adhesion molecule (LFA-2) that binds to LFA-3. It is not as specific for the T-cell lineage as CD3. * **CD19:** This is a classic **pan-B lymphocyte marker** [2]. It is expressed on B-cells from the earliest stages of B-cell development until the plasma cell stage [2]. * **CD25:** This is the alpha chain of the **IL-2 receptor**. It is not a pan-marker; rather, it is a marker of **activated T-cells** and is constitutively expressed on **Regulatory T-cells (Tregs)**. **High-Yield Clinical Pearls for NEET-PG:** * **Pan-B markers:** CD19, CD20 (Target of Rituximab), and CD22 [2]. * **NK cell markers:** CD16 (FcγRIII) and CD56. * **Hassall’s Corpuscles:** Found in the thymus; they are characteristic of T-cell maturation sites. * **Flow Cytometry:** The gold standard technique for identifying these clusters of differentiation (CD) markers in leukemias and lymphomas. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 198-199. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of White Blood Cells, Lymph Nodes, Spleen, and Thymus, p. 598.

Q: Cell-mediated lysis of tumor cells is mediated by?

HLA Class I. **Explanation:** **1. Why HLA Class I is correct:** Cell-mediated immunity against tumor cells primarily involves **CD8+ Cytotoxic T Lymphocytes (CTLs)** [1]. These T cells are specialized to recognize and kill "altered-self" cells, such as those infected by viruses or transformed into tumors. For a CTL to recognize a tumor cell, the tumor-associated antigen must be processed and presented on the cell surface in association with **HLA Class I molecules** (HLA-A, B, or C) [1]. This interaction triggers the release of perforins and granzymes, leading to apoptosis of the tumor cell. **2. Why other options are incorrect:** * **HLA Class II:** These molecules (HLA-DR, DP, DQ) are primarily expressed on **Antigen-Presenting Cells (APCs)** like dendritic cells and macrophages. They present exogenous antigens to **CD4+ Helper T cells** [1]. While CD4+ cells coordinate the immune response, they do not directly mediate the lysis of tumor cells. * **HLA Class III:** These genes encode components of the complement system (C2, C4) and certain cytokines (TNF-α). They are not involved in antigen presentation or direct T-cell recognition. **Clinical Pearls for NEET-PG:** * **Rule of 8:** Remember that MHC I × CD8 = 8 and MHC II × CD4 = 8. * **Tumor Evasion:** One common mechanism by which tumors escape immune surveillance is the **downregulation of HLA Class I expression**, making them "invisible" to CD8+ T cells. * **NK Cells:** If a tumor cell loses HLA Class I expression, it becomes a target for **Natural Killer (NK) cells**, which provide a backup defense mechanism (the "missing self" hypothesis). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 318-319.

Q: Which of the following statements about acute hemolytic blood transfusion reactions is true?

Complement mediated hemolysis is seen.. **Explanation:** **Acute Hemolytic Transfusion Reaction (AHTR)** is a medical emergency typically caused by **ABO incompatibility** [2]. 1. **Why Option A is correct:** AHTR is a classic example of **Type II Hypersensitivity**. When incompatible blood is transfused, pre-existing host IgM antibodies (isohemagglutinins) bind to donor red cell antigens. This triggers the **classical complement pathway**, leading to the formation of the Membrane Attack Complex (MAC) [2]. This results in rapid **intravascular hemolysis**, releasing free hemoglobin into the plasma [1]. 2. **Why other options are incorrect:** * **Option B:** AHTR is a **Type II hypersensitivity** (antibody-mediated cytotoxicity), not Type III (immune-complex mediated). * **Option C:** These reactions are **highly life-threatening**. They can rapidly progress to disseminated intravascular coagulation (DIC), shock, and multi-organ failure [2]. * **Option D:** Renal blood flow is **severely compromised**. Free hemoglobin is nephrotoxic and can cause **Acute Tubular Necrosis (ATN)** [1]. Furthermore, systemic hypotension and DIC-induced microthrombi lead to acute renal failure. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause:** Clerical/Administrative error (wrong blood to wrong patient) [2]. * **Triad of symptoms:** Fever/Chills, Flank pain (due to renal ischemia), and Hemoglobinuria [1]. * **Lab Findings:** Positive Direct Antiglobulin Test (DAT/Coombs), decreased haptoglobin, and increased indirect bilirubin [1]. * **Management:** Immediate cessation of transfusion and aggressive IV fluid resuscitation to maintain urine output. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Red Blood Cell and Bleeding Disorders, pp. 639-640. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Red Blood Cell and Bleeding Disorders, pp. 673-674.

Question 1

Which of the following is a pan-T lymphocyte marker?

Accepted Answer

CD3

Answer

CD2

Answer

CD19

Answer

CD25

Question 2

Hyperacute graft rejection is caused by which of the following mechanisms?

Accepted Answer

Preformed antibodies

Answer

T-lymphocytes

Answer

Macrophages

Answer

B-lymphocytes

Question 3

Cell-mediated lysis of tumor cells is mediated by?

Accepted Answer

HLA Class I

Answer

HLA Class II

Answer

HLA Class III

Answer

All of the above

Question 4

Which of the following statements is not true regarding Churg-Strauss syndrome?

Accepted Answer

Intravascular granulomas are a typical feature.

Answer

Asthma is commonly present.

Answer

Peripheral eosinophilia is a characteristic finding.

Answer

It involves vasculitis affecting multiple organ systems.

Question 5

L.E. Cell phenomenon in peripheral blood is seen in:

Accepted Answer

Systemic Lupus Erythematosus

Answer

Rheumatic heart disease

Answer

Infective endocarditis

Answer

Ischemic heart disease

Question 6

Which of the following statements about acute hemolytic blood transfusion reactions is true?

Accepted Answer

Complement mediated hemolysis is seen.

Answer

Type III hypersensitivity is responsible for most cases.

Answer

These reactions are rarely life-threatening.

Answer

Renal blood flow is always maintained.

Question 7

Hyperacute rejection is due to:

Accepted Answer

Preformed antibodies

Answer

Cytotoxic T-lymphocyte mediated injury

Answer

Circulating macrophage mediated injury

Answer

Endothelitis caused by donor antibodies

Question 8

Graft vs Host reaction can be reduced by which of the following methods?

Accepted Answer

Irradiation

Answer

Leukoreduction/Leukofiltration

Answer

Immunosuppression

Answer

Buffy coat removal

Question 9

What is the first line of defense against tumors and viruses?

Accepted Answer

NK cell

Answer

T cell

Answer

Histiocyte

Answer

Macrophage

Question 10

Which of the following is caused by C1 inhibitor deficiency?

Accepted Answer

Hereditary angioneurotic edema

Answer

Systemic lupus erythematosus

Answer

Severe recurrent pyogenic infection

Answer

Collagen vascular disease

Immunopathology — MCQs

Immunopathology — MCQs

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