Blood and Immunity — MCQs

Blood and Immunity Indian Medical PG Practice Questions and MCQs

Question 251: Tissue macrophages are derived from which cell lineage?

A. Neutrophil
B. Eosinophil
C. Monocyte (Correct Answer)
D. All of the above

Explanation: **Explanation:** **1. Why Monocyte is Correct:** Tissue macrophages are part of the **Mononuclear Phagocyte System** (formerly known as the Reticuloendothelial System). Monocytes are produced in the bone marrow and released into the peripheral blood, where they circulate for about 10–20 hours. Once they migrate into various tissues, they undergo morphological and functional changes to become **Tissue Macrophages**. These cells are larger, contain more lysosomes, and possess a high capacity for phagocytosis and antigen presentation. **2. Why Other Options are Incorrect:** * **Neutrophils (A):** These are "microphages." While they are professional phagocytes and the first responders to acute inflammation, they are short-lived (hours to days) and do not transform into permanent tissue macrophages. * **Eosinophils (B):** These are specialized granulocytes primarily involved in allergic reactions and defense against helminthic (parasitic) infections. They do not differentiate into macrophages. * **All of the above (D):** This is incorrect because the lineage is specific to the monocyte-macrophage cell line. **3. High-Yield Clinical Pearls for NEET-PG:** * **Specific Tissue Macrophages (Must-know for exams):** * Liver: **Kupffer cells** * CNS: **Microglia** * Lungs: **Alveolar macrophages** (Dust cells) * Skin: **Langerhans cells** * Bone: **Osteoclasts** * Kidney: **Mesangial cells** * Placenta: **Hofbauer cells** * **Function:** Macrophages act as a bridge between innate and adaptive immunity by acting as **Antigen Presenting Cells (APCs)** via MHC II molecules. * **Cytokines:** They are the primary source of **IL-1, IL-6, and TNF-alpha**.

Question 252: Which of the following are Vitamin K dependent coagulation factors?

A. II and III
B. IX and X (Correct Answer)
C. III and V
D. VIII and XII

Explanation: **Explanation:** Vitamin K is an essential cofactor for the enzyme **gamma-glutamyl carboxylase**. This enzyme adds a carboxyl group to glutamate residues on specific clotting factors, a process known as **gamma-carboxylation**. This modification allows these factors to bind calcium ions ($Ca^{2+}$) and attach to phospholipid membranes, which is critical for the coagulation cascade. The Vitamin K-dependent factors are **II (Prothrombin), VII, IX, and X**, as well as the anticoagulant proteins **C and S**. **Analysis of Options:** * **Option B (Correct):** Factors IX (Christmas factor) and X (Stuart-Prower factor) are both Vitamin K-dependent. * **Option A (Incorrect):** While Factor II is Vitamin K-dependent, **Factor III (Tissue Factor)** is not; it is a cell surface glycoprotein. * **Option C (Incorrect):** Neither **Factor III** nor **Factor V (Labile factor)** requires Vitamin K for synthesis. Factor V acts as a cofactor for Factor Xa. * **Option D (Incorrect):** **Factor VIII** (Anti-hemophilic factor) and **Factor XII** (Hageman factor) are synthesized independently of Vitamin K. **High-Yield Clinical Pearls for NEET-PG:** * **Warfarin Mechanism:** Warfarin inhibits **Vitamin K Epoxide Reductase (VKOR)**, preventing the recycling of Vitamin K and thus inhibiting the synthesis of these factors. * **Monitoring:** Warfarin therapy is monitored using **PT/INR** (primarily reflecting Factor VII levels due to its shortest half-life). * **Half-life:** Factor VII has the shortest half-life (~6 hours), while Factor II has the longest (~60 hours). * **Newborns:** Neonates are Vitamin K deficient due to sterile guts and poor placental transfer; hence, a prophylactic Vitamin K injection is given at birth to prevent **Hemorrhagic Disease of the Newborn**.

Question 253: What is the serum fibrinogen threshold considered adequate to promote coagulation?

A. 100 mg%
B. 150 mg% (Correct Answer)
C. 200 mg%
D. 250 mg%

Explanation: **Explanation:** **Fibrinogen (Factor I)** is a high-molecular-weight plasma protein synthesized in the liver. It is the precursor to fibrin, which forms the structural meshwork of a blood clot. In a healthy individual, normal plasma fibrinogen levels range between **200–400 mg/dL**. 1. **Why 150 mg% is correct:** While the body can technically initiate clotting at lower levels, **150 mg/dL** is clinically recognized as the critical threshold required to maintain adequate hemostasis during physiological stress or surgery. Below this level, the strength and stability of the fibrin clot are significantly compromised, leading to an increased risk of bleeding. In clinical guidelines (such as those for Postpartum Hemorrhage or Trauma-Induced Coagulopathy), 150 mg/dL is often the trigger point for replacement therapy. 2. **Analysis of Incorrect Options:** * **100 mg%:** This is the threshold for "hypofibrinogenemia." While clotting can occur, it is often insufficient for surgical hemostasis. * **200 mg% & 250 mg%:** These values fall within the **normal physiological range**. While they are "adequate," they do not represent the minimum threshold or the critical "cut-off" point usually tested in exams regarding the promotion of coagulation in deficiency states. **High-Yield Clinical Pearls for NEET-PG:** * **Acute Phase Reactant:** Fibrinogen levels rise during inflammation, pregnancy, and stress. * **ESR Correlation:** Fibrinogen is the most important plasma protein contributing to the **Erythrocyte Sedimentation Rate (ESR)** by neutralizing the negative charge on RBCs (zeta potential), promoting rouleaux formation. * **Cryoprecipitate:** This is the blood product of choice for fibrinogen replacement, as it contains high concentrations of Factor I, VIII, XIII, and vWF. * **Afibrinogenemia:** A rare congenital condition where fibrinogen is undetectable, leading to severe bleeding diathesis.

Question 254: Thrombopoietin is produced by which organ?

A. Monocytes
B. Liver (Correct Answer)
C. Megakaryocytes
D. Megakaryoblasts

Explanation: **Explanation:** **Thrombopoietin (TPO)** is the primary glycoprotein hormone responsible for regulating platelet production (thrombopoiesis). It stimulates the proliferation and maturation of megakaryocytes from myeloid progenitor cells. 1. **Why Liver is Correct:** The **liver** is the primary site of Thrombopoietin synthesis (constituting about 90% of production), specifically by parenchymal cells and sinusoidal endothelial cells. The remaining 10% is produced by the proximal convoluted tubules of the **kidneys** and small amounts in the smooth muscle of the marrow. Unlike Erythropoietin (which is primarily renal), TPO is primarily hepatic. 2. **Why Other Options are Incorrect:** * **Monocytes:** These are leukocytes involved in phagocytosis and cytokine production (like IL-6), but they do not synthesize TPO. * **Megakaryocytes and Megakaryoblasts:** These are the **target cells** for TPO, not the source. TPO binds to the **c-Mpl receptor** on these cells to induce maturation. While platelets can internalize and degrade TPO (regulating its plasma levels), they do not produce it. **High-Yield Clinical Pearls for NEET-PG:** * **Regulation:** TPO production is largely **constitutive** (constant). Plasma levels are regulated by "platelet mass"—platelets have c-Mpl receptors that bind and destroy TPO. Therefore, in thrombocytopenia, less TPO is cleared, leading to higher circulating levels to stimulate the marrow. * **Clinical Correlation:** In **Liver Cirrhosis**, thrombopoietin production decreases, which is a major contributing factor to the thrombocytopenia seen in chronic liver disease. * **Drug Link:** **Romiplostim** and **Eltrombopag** are TPO receptor agonists used to treat ITP and aplastic anemia.

Question 255: Which interleukin is primarily produced by macrophages?

A. IL-1 (Correct Answer)
B. IL-2
C. IL-3
D. IL-4

Explanation: **Explanation:** **Interleukin-1 (IL-1)** is a key pro-inflammatory cytokine primarily produced by **activated macrophages** and monocytes. It plays a central role in the innate immune response by acting as an endogenous pyrogen (inducing fever via the hypothalamus), stimulating T-cell activation, and promoting the synthesis of acute-phase reactants by the liver. **Analysis of Options:** * **IL-1 (Correct):** Produced by macrophages. It mediates inflammation and induces the expression of adhesion molecules on endothelial cells. * **IL-2:** Produced primarily by **Th1 cells** (T-lymphocytes). It acts as a T-cell growth factor, stimulating the proliferation of T and B cells. * **IL-3:** Produced by **activated T-cells**. It functions as a colony-stimulating factor, supporting the growth and differentiation of hematopoietic stem cells in the bone marrow. * **IL-4:** Produced by **Th2 cells** and mast cells. It promotes B-cell differentiation into plasma cells and induces "class switching" to **IgE** and IgG4. **High-Yield NEET-PG Pearls:** * **Hot T-Bone Steak** (Mnemonic for IL 1-5): * **IL-1:** **Hot** (Fever/Pyrogen). * **IL-2:** Stimulates **T**-cells. * **IL-3:** Stimulates **Bone** marrow. * **IL-4:** Stimulates Ig**E** production. * **IL-5:** Stimulates Ig**A** production and Eosinophils. * **IL-6** is also a major product of macrophages and is the primary inducer of **CRP (C-Reactive Protein)**. * **IL-8** is the chief chemotactic factor for **Neutrophils** ("Clean up on aisle 8").

Question 256: What is the normal Packed Cell Volume (PCV) value?

A. 30-35%
B. 40-45% (Correct Answer)
C. 50-55%
D. 60-65%

Explanation: **Explanation:** **Packed Cell Volume (PCV)**, also known as **Hematocrit (Hct)**, represents the percentage of total blood volume occupied by red blood cells (RBCs) after centrifugation. It is a critical indicator of a patient’s hydration status and RBC mass. * **Why Option B is Correct:** In healthy adults, the normal range for PCV is approximately **40–45%**. Specifically, it is slightly higher in males (42–52%) and lower in females (37–47%) due to the influence of testosterone on erythropoiesis and menstrual blood loss. Option B (40-45%) represents the most accurate physiological mean for the general population. * **Why Other Options are Incorrect:** * **Option A (30-35%):** These values indicate **Anemia** or hemodilution (e.g., pregnancy or fluid overload). * **Options C & D (50-65%):** These values are abnormally high, indicating **Polycythemia** (primary or secondary) or severe dehydration (hemoconcentration). A PCV >60% significantly increases blood viscosity, raising the risk of thrombosis. **High-Yield Clinical Pearls for NEET-PG:** 1. **Wintrobe’s Tube:** Used for macro-determination of PCV and ESR. The tube is 110 mm long with a 3 mm bore. 2. **Buffy Coat:** After centrifugation, a thin white layer (approx. 1%) appears between the plasma and RBCs, containing WBCs and platelets. 3. **Rule of Three:** In a healthy individual, Hemoglobin (g/dL) × 3 ≈ PCV (%). 4. **Pregnancy:** PCV decreases (Physiological Anemia) because the increase in plasma volume (approx. 40-50%) outweighs the increase in RBC mass (approx. 20-30%).

Question 257: The vitamin K-dependent proteins C and S inactivate which factors?

A. Factor 8a and 5a (Correct Answer)
B. Factor 7a and 5b
C. Factor 3a and 3b
D. All of the above

Explanation: **Explanation:** The correct answer is **Factor 8a and 5a**. **Mechanism of Action:** Proteins C and S are natural anticoagulants synthesized in the liver in a Vitamin K-dependent manner. The process begins when **Thrombin** binds to **Thrombomodulin** on the endothelial surface. This complex activates Protein C into **Activated Protein C (APC)**. APC, using **Protein S as a cofactor**, proteolytically inactivates the active forms of the cofactors **Factor Va** and **Factor VIIIa**. By degrading these factors, the Protein C system inhibits the "prothrombinase complex" and the "tenase complex," effectively slowing down the coagulation cascade and preventing excessive clot formation. **Analysis of Incorrect Options:** * **Option B (7a and 5b):** Factor VIIa is inhibited by Tissue Factor Pathway Inhibitor (TFPI), not Protein C. "Factor 5b" is not a standard physiological term in the coagulation cascade. * **Option C (3a and 3b):** Factor III is Tissue Factor. It is not a target for Protein C/S inactivation. * **Option D:** Incorrect, as the action is specific to the cofactors of the common and intrinsic pathways (Va and VIIIa). **High-Yield Clinical Pearls for NEET-PG:** * **Factor V Leiden:** The most common inherited cause of hypercoagulability (thrombophilia). It involves a mutation in Factor V that makes it resistant to inactivation by Activated Protein C. * **Warfarin-Induced Skin Necrosis:** Occurs in patients with underlying Protein C deficiency. Since Protein C has a shorter half-life than procoagulant factors (II, VII, IX, X), starting Warfarin creates a transient hypercoagulable state, leading to microvascular thrombosis. * **Vitamin K-dependent factors:** Procoagulants (II, VII, IX, X) and Anticoagulants (Protein C, S, and Z).

Question 258: Serum lacks which of the following clotting factors?

A. 2, 5, 7, 8 (Correct Answer)
B. 2, 5, 7, 8, 9
C. 8, 9
D. 8, 9, 10

Explanation: ### Explanation The fundamental difference between **plasma** and **serum** lies in the process of coagulation. Plasma is the liquid portion of unclotted blood (containing all clotting factors), whereas **serum** is the fluid remaining after blood has clotted. **1. Why Option A is Correct:** During the formation of a clot, specific clotting factors are consumed as they are converted into their active forms or incorporated into the fibrin meshwork. * **Factor 2 (Prothrombin):** Converted into thrombin. * **Factor 5 (Proaccelerin) and Factor 8 (Anti-hemophilic factor):** These act as co-factors that are consumed during the cascade. * **Factor 1 (Fibrinogen):** Converted into the insoluble fibrin clot (though not listed in the option, it is also absent). * **Factor 13:** Consumed to cross-link fibrin. * **Factor 7:** While its role is catalytic, it is significantly depleted/absent in serum following the activation of the extrinsic pathway. **2. Why Other Options are Incorrect:** * **Options B, C, and D:** These include **Factor 9 and Factor 10**. These factors are proteases that remain in the serum in their activated or precursor forms; they are not fully consumed during the clotting process. Serum is specifically defined by the absence of the "consumable" factors (1, 2, 5, 8, and 13). **3. NEET-PG High-Yield Pearls:** * **Formula:** Serum = Plasma – Clotting Factors (1, 2, 5, 8, 13). * **Serotonin:** Serum has a higher concentration of serotonin than plasma because it is released by platelets during clotting. * **Electrolytes:** Potassium levels are slightly higher in serum than in plasma due to release from platelets during the clotting process. * **Clinical Use:** Serum is preferred for most serological tests and clinical chemistry (e.g., LFTs, KFTs) because anticoagulants in plasma can interfere with certain enzymatic reactions.

Question 259: What is the effect of G-CSF and GM-CSF on hematopoiesis?

A. Leukocytosis (Correct Answer)
B. Erythrocytosis
C. Leukopenia
D. Thrombocytosis

Explanation: **Explanation:** **G-CSF (Granulocyte Colony-Stimulating Factor)** and **GM-CSF (Granulocyte-Macrophage Colony-Stimulating Factor)** are potent hematopoietic growth factors that regulate the proliferation and differentiation of myeloid progenitor cells. 1. **Why Leukocytosis is Correct:** * **G-CSF** specifically stimulates the production and release of **neutrophils** from the bone marrow. * **GM-CSF** has a broader spectrum, stimulating the production of **neutrophils, monocytes, and eosinophils**. * The administration or endogenous surge of these factors leads to an increase in the total white blood cell (WBC) count, a condition known as **Leukocytosis**. 2. **Why Other Options are Incorrect:** * **Erythrocytosis:** This is primarily regulated by **Erythropoietin (EPO)**, which acts on erythroid precursors. G-CSF/GM-CSF do not significantly impact red cell mass. * **Leukopenia:** This refers to a decrease in WBCs. G-CSF and GM-CSF are actually used clinically to *reverse* leukopenia (specifically neutropenia). * **Thrombocytosis:** Platelet production is primarily regulated by **Thrombopoietin (TPO)**. While some cytokines have cross-reactivity, G-CSF is not a primary driver of platelet elevation. **Clinical Pearls for NEET-PG:** * **Filgrastim:** A recombinant G-CSF used to treat chemotherapy-induced neutropenia. * **Sargramostim:** A recombinant GM-CSF used in bone marrow transplantation. * **Side Effect:** The most common side effect of G-CSF therapy is **bone pain**, due to the rapid expansion of cells within the marrow cavity. * **Stem Cell Harvest:** G-CSF is used to "mobilize" hematopoietic stem cells (CD34+) from the bone marrow into the peripheral blood for collection.

Question 260: Nitric oxide produces its anti-aggregatory action by increasing the levels of which second messenger?

A. cAMP
B. cGMP (Correct Answer)
C. ADP
D. Phosphoinositol

Explanation: **Explanation:** **Mechanism of Action (Why B is correct):** Nitric Oxide (NO), also known as Endothelium-Derived Relaxing Factor (EDRF), is a potent inhibitor of platelet aggregation. It diffuses across the platelet membrane and binds to the heme group of **soluble Guanylyl Cyclase (sGC)**. This activation leads to the conversion of GTP into **cyclic Guanylyl Monophosphate (cGMP)**. Elevated levels of cGMP activate Protein Kinase G (PKG), which reduces intracellular calcium levels and inhibits the activation of GPIIb/IIIa receptors, thereby preventing platelet aggregation and maintaining vascular patency. **Analysis of Incorrect Options:** * **A. cAMP:** While increased cAMP also inhibits platelet aggregation (the mechanism used by Prostacyclin/PGI2), it is not the primary second messenger for Nitric Oxide. * **C. ADP:** Adenosine Diphosphate is a potent **pro-aggregatory** agent stored in platelet delta-granules. It promotes aggregation by binding to P2Y1 and P2Y12 receptors. * **D. Phosphoinositol:** The IP3/DAG pathway typically leads to an increase in intracellular calcium, which **promotes** platelet activation and degranulation, opposing the action of NO. **High-Yield Clinical Pearls for NEET-PG:** * **Synergy:** NO and PGI2 act synergistically to prevent intravascular clotting; NO uses the cGMP pathway, while PGI2 uses the cAMP pathway. * **Nitroprusside/Nitroglycerin:** These drugs act as NO donors, utilizing this same cGMP pathway to cause vasodilation and anti-platelet effects. * **Phosphodiesterase Inhibitors:** Drugs like Sildenafil prevent the breakdown of cGMP, prolonging the effects of NO.

Practice by Chapter

Composition and Functions of Blood

Practice Questions

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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