Blood and Immunity — MCQs

Blood and Immunity Indian Medical PG Practice Questions and MCQs

Question 481: Which of the following is a procoagulant protein?

A. Thrombin (Correct Answer)
B. Protein S
C. Thrombomodulin
D. Protein C

Explanation: ***Thrombin*** - Thrombin is a key **procoagulant enzyme** that catalyzes the conversion of fibrinogen to fibrin in the clotting cascade [2] [3]. - It activates platelets and enhances thrombus formation, playing a crucial role in **hemostasis** [1] [2]. *Protein C* - Protein C functions as an **anticoagulant**; when activated, it inactivates factors Va and VIIIa to decrease clot formation [1]. - Low levels or dysfunction of Protein C lead to increased thrombotic risk, indicating its role in **regulating coagulation** rather than promoting it. *Protein S* - Like Protein C, Protein S is involved in the **anticoagulation pathway**, serving as a cofactor to activated Protein C. - It assists in the inactivation of the procoagulant factors Va and VIIIa, thereby reducing coagulation. *Thrombomodulin* - Thrombomodulin is a receptor that binds thrombin, altering its activity from procoagulant to anticoagulant by activating Protein C. - Its primary function is to regulate coagulation rather than to promote clot formation, underscoring its role in **coagulation inhibition**. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 582-583. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Hemodynamic Disorders, Thromboembolic Disease, and Shock, p. 130. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Hemodynamic Disorders, Thromboembolic Disease, and Shock, pp. 128-130.

Question 482: Which of the following conditions is classified as anemic hypoxia?

A. CO poisoning (Correct Answer)
B. Cyanide poisoning
C. COPD
D. High altitude

Explanation: ***CO poisoning*** - In **carbon monoxide poisoning**, CO binds to **hemoglobin** with an affinity much higher than oxygen, forming carboxyhemoglobin. - This binding reduces the **oxygen-carrying capacity** of the blood, leading to anemic hypoxia despite normal arterial PO2. *Cyanide poisoning* - **Cyanide poisoning** causes **histotoxic hypoxia**, as it inhibits cellular respiration by blocking cytochrome c oxidase. - While oxygen delivery to tissues may be normal, the cells cannot utilize the oxygen. *COPD* - **COPD (Chronic Obstructive Pulmonary Disease)** causes **hypoxic hypoxia** due to impaired gas exchange in the lungs. - This results in low arterial PO2 because of ventilation-perfusion mismatch. *High altitude* - **High altitude** leads to **hypoxic hypoxia** due to reduced atmospheric partial pressure of oxygen. - This results in a decreased alveolar and arterial PO2, reducing oxygen loading onto hemoglobin.

Question 483: What is the primary function of Langerhans' cells?

A. Antigen presenting cells (Correct Answer)
B. Involved in immune responses
C. Phagocytosis of pathogens
D. Keratinocyte production and maintenance

Explanation: ***Antigen presenting cells*** - Langerhans' cells play a critical role as **antigen presenting cells** (APCs) in the immune system, facilitating the activation of T-cells [1][2]. - They are found in the **epidermis** and are essential in initiating immune responses against pathogens [1][3]. *Seen in auto immune conditions* - While Langerhans' cells may be involved in autoimmune responses, they are not exclusively seen in these conditions. - Their primary function isn't linked to autoimmunity but rather to **immunological surveillance** and **antigen presentation** [1]. *Phagocytic cells* - Langerhans' cells are not primarily **phagocytic**, as their main role focuses on presenting antigens rather than directly engulfing pathogens [1]. - Phagocytic cells include macrophages and neutrophils, which are more involved in **directly consuming foreign particles**. *Seen in chronic infection* - Although Langerhans' cells can participate in the immune response during infections, they are not specifically characterized as being prominent in **chronic infections**. - Chronic infections are typically associated with different immune cell dynamics, involving other cells such as **plasma cells** and **T-cells**. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 200. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 207-208. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Skin, p. 1144.

Question 484: Among the blood cells, which has the longest lifespan?

A. Neutrophils
B. Eosinophils
C. Lymphocytes
D. Erythrocytes (Correct Answer)

Explanation: ***Erythrocytes*** - Erythrocytes (red blood cells) have the **longest consistent lifespan** among blood cells at approximately **100-120 days** in circulation. - They are produced in the bone marrow and removed by the **reticuloendothelial system** (primarily spleen and liver) when they become senescent. - This predictable lifespan makes RBCs the blood cells with the longest average survival time. *Lymphocytes* - While some **memory lymphocytes** can survive for months to years, the **majority of lymphocytes are short-lived** (days to weeks). - The question asks about blood cells in general, not the specialized subset of long-lived memory cells. - Most naive and activated lymphocytes undergo apoptosis within days. *Neutrophils* - Neutrophils are **short-lived granulocytes**, typically circulating for only **6-12 hours** in the bloodstream. - Their primary role is in acute inflammation and bacterial defense, after which they undergo apoptosis. *Eosinophils* - Eosinophils have a short lifespan, circulating for **6-12 hours** in the blood before migrating into tissues. - They are primarily involved in allergic reactions and defense against parasitic infections.

Question 485: The clot formed after the coagulation cascade is not stable unless extensive cross-linking occurs. This is done by what?

A. Plasmin
B. Factor XIII (Correct Answer)
C. Fibrinogen
D. Kininogen

Explanation: ***Factor XIII*** - **Factor XIII** (fibrin-stabilizing factor) is crucial for cross-linking fibrin strands, forming a stable clot [1][2]. - This enzyme catalyzes the conversion of soluble fibrin into insoluble fibrin by creating **covalent bonds** between fibrin molecules. *Thrombin* - While **thrombin** is essential for converting fibrinogen to fibrin, it does not facilitate the cross-linking of fibrin strands. - Thrombin acts primarily in the early stages of the coagulation cascade and is not responsible for clot stabilization. *Plasmin* - **Plasmin** is involved in fibrinolysis, the breakdown of fibrin clots, rather than stabilizing them. - It works to dissolve clots after they have formed, which is the opposite of the function required for cross-linking. *High molecular weight kininogen* - This protein is a precursor in the **kallikrein-kinin system** and is involved in the inflammatory response, not in clot stabilization. - High molecular weight kininogen assists in **bradykinin** formation but does not play a role in cross-linking fibrin for stable clots. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Hemodynamic Disorders, Thromboembolic Disease, and Shock, p. 130. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 582-583.

Question 486: What is the estimated amount of iron delivered from the transfusion of 2 units of packed red cells?

A. 500mg (Correct Answer)
B. 1g
C. 100mg
D. 250mg

Explanation: ***500mg*** - Each unit of **packed red blood cells (PRBCs)** contains approximately **250 mg of iron**. - Therefore, two units would deliver approximately **500 mg of iron** to the recipient. *1g* - This amount would typically be derived from four units of PRBCs, which is double the number of units specified in the question. - This level of iron is usually associated with more significant transfusion burden, as seen in patients with chronic transfusions. *100mg* - This amount represents less than half the iron content of a single unit of PRBCs, making it an underestimation. - One unit of PRBCs contains approximately 200-250 mg of iron, so 100 mg is insufficient. *250mg* - This is the approximate iron content of a single unit of PRBCs, not the two units mentioned in the question. - The question specifically asks for the iron content from two units of PRBCs, requiring a cumulative calculation.

Question 487: Most efficient antigen-presenting cell in the skin is?

A. Dendritic cell
B. Macrophages
C. Langerhans cell (Correct Answer)
D. Kupffer cells

Explanation: ***Langerhans cell*** - **Langerhans cells** are specialized dendritic cells found in the **epidermis** and are the primary professional antigen-presenting cells (APCs) of the skin. - They are highly efficient at capturing and processing antigens, then migrating to regional **lymph nodes** to activate T lymphocytes. *Dendritic cell* - While Langerhans cells are a type of **dendritic cell**, the term "dendritic cell" is broader and includes various populations found in different tissues. - In the context of the skin, the specific and most efficient type of dendritic cell is the Langerhans cell. *Macrophages* - **Macrophages** are phagocytic cells that can present antigens, but they are generally less efficient at initiating primary T-cell responses compared to professional APCs like Langerhans cells. - They are found in the dermis but play a secondary role in initiating skin-specific immune responses compared to Langerhans cells. *Kupffer cells* - **Kupffer cells** are specialized macrophages found in the **liver sinusoids**. - They are primarily involved in filtering blood and presenting antigens within the liver, not in the skin.

Question 488: Which of the following interleukins is primarily raised during a fever?

A. IL-10
B. IL-2
C. IL-1β
D. IL-6 (Correct Answer)

Explanation: ***IL-6*** - **IL-6** is a **pro-inflammatory cytokine** that plays a central role in the acute phase response and is a major mediator of fever. - It acts on the **hypothalamus** to increase the body's set point temperature, leading to fever. *IL-1β* - While **IL-1β** is also a **pyrogenic cytokine** that contributes to fever, IL-6 is often cited as the primary driver due to its strong effect on the acute phase response and direct action on the thermoregulatory center. - **IL-1β** stimulates the production of other inflammatory mediators, including IL-6, which then directly influences fever. *IL-10* - **IL-10** is an **anti-inflammatory cytokine** that primarily functions to suppress immune responses and reduce inflammation, not induce fever. - Its role is to **downregulate the production** of pro-inflammatory cytokines, thus counteracting the effects that would lead to fever. *IL-2* - **IL-2** is primarily involved in the **growth, proliferation, and differentiation of T cells** during an immune response. - While it plays a crucial role in cellular immunity, it is not considered a primary mediator of fever.

Question 489: Which of the following cell types is not a precursor of erythrocytes?

A. Proerythroblast
B. Normoblast
C. Reticulocyte
D. Myeloblast (Correct Answer)

Explanation: ***Myeloblast*** - **Myeloblasts** are immature precursor cells that differentiate into **granulocytes** (neutrophils, eosinophils, basophils) within the myeloid lineage. - They are part of **granulopoiesis**, not erythropoiesis, and thus do not give rise to red blood cells. *Proerythroblast* - The **proerythroblast** is the earliest recognizable precursor cell in the erythroid lineage that develops from the common myeloid progenitor. - It differentiates into basophilic, polychromatophilic, and orthochromatic erythroblasts. *Normoblast* - **Normoblasts** (also known as erythroblasts) represent an intermediate stage in erythrocyte maturation, encompassing basophilic, polychromatophilic, and orthochromatic forms. - These cells undergo progressive hemoglobin synthesis and nuclear condensation, eventually leading to nuclear extrusion. *Reticulocyte* - A **reticulocyte** is an immature red blood cell that still contains ribosomal RNA, giving it a reticular appearance when stained with supravital dyes. - Reticulocytes mature into fully functional **erythrocytes** within 1-2 days after being released from the bone marrow into circulation.

Question 490: All of the following are pyrogenic cytokines, EXCEPT:

A. Interleukin 6 (IL-6)
B. Tumor Necrosis Factor (TNF)
C. Interferon alpha (IFN-α)
D. Interleukin 18 (IL-18) (Correct Answer)

Explanation: ***Interleukin 18 (IL-18)*** - IL-18 is not considered a **pyrogenic cytokine**; instead, it plays a role in **enhancing Th1 responses** and supporting cell-mediated immunity. - While it does have inflammatory properties, its main functions are related to **activation of T and NK cells**, not direct pyrogenic effects. *Interleukin 6 (IL-6)* - IL-6 is a classic **pyrogenic cytokine** that induces fever by acting on the hypothalamus. - It plays a significant role in the **acute phase response** and inflammation. *Tumor Necrosis Factor (TNF)* - TNF is another well-known **pyrogenic cytokine**, involved in systemic inflammation and inducing fever [1]. - It also promotes apoptosis and acts on the hypothalamus to raise body temperature. *Interferon alpha (IFN-α)* - IFN-α is involved in the immune response against **viral infections** and also has some role in **fever induction**, but is not classified primarily as a pyrogenic cytokine. - It primarily functions through **antiviral activity** and stimulation of immune cells rather than inducing fever directly [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 97.

Practice by Chapter

Composition and Functions of Blood

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Erythrocytes and Hemoglobin

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Leukocytes and Immune Function

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Platelets and Hemostasis

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Blood Groups and Transfusion

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Coagulation and Fibrinolysis

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Hematopoiesis

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Innate Immunity

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Adaptive Immunity

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Immunological Memory and Tolerance

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