Blood and Immunity — MCQs

Blood and Immunity Indian Medical PG Practice Questions and MCQs

Question 101: Which of the following cytokines is NOT a hematopoietin?

A. IL-2
B. IL-4
C. IL-7
D. IL-8 (Correct Answer)

Explanation: ### Explanation The **Hematopoietin family** (also known as Class I cytokines) is a large group of cytokines characterized by a specific four-alpha-helix bundle structure. These cytokines play critical roles in the proliferation and differentiation of various immune cells. **Why IL-8 is the correct answer:** **IL-8 (CXCL8)** is not a hematopoietin; it belongs to the **Chemokine** family. Specifically, it is a CXC chemokine produced by macrophages and endothelial cells. Its primary function is **chemotaxis**, acting as a potent chemoattractant that recruits neutrophils to sites of inflammation. It does not share the structural motif or the specific signaling pathways (typically involving the JAK-STAT pathway) characteristic of the hematopoietin family. **Why the other options are incorrect:** * **IL-2:** A classic hematopoietin that acts as a T-cell growth factor, essential for the proliferation of T-lymphocytes. * **IL-4:** A hematopoietin that promotes B-cell differentiation into IgE-producing plasma cells and drives Th2 cell development. * **IL-7:** A vital hematopoietin produced by bone marrow stromal cells, necessary for the survival and development of B and T cell precursors (lymphopoiesis). **High-Yield Facts for NEET-PG:** * **Hematopoietin Family Members:** Includes IL-2 through IL-7, IL-9, IL-11, IL-13, IL-15, Erythropoietin (EPO), and Granulocyte-Colony Stimulating Factor (G-CSF). * **IL-8 Mnemonic:** "Clean up on aisle 8"—IL-8 recruits neutrophils to "clean up" the site of infection. * **Receptor Association:** Most hematopoietins signal through receptors that share common subunits, such as the **common gamma chain ($\gamma$c)**; mutations in this chain lead to X-linked Severe Combined Immunodeficiency (SCID).

Question 102: What is the normal ratio of CD4 (T4) to CD8 (T8) cells?

A. 2:1 (Correct Answer)
B. 1:2
C. 3:1
D. 1:3

Explanation: **Explanation:** The normal CD4:CD8 ratio in a healthy adult peripheral blood sample typically ranges from **1.5 to 2.5**, with **2:1** being the standard physiological average. **1. Why 2:1 is correct:** CD4+ cells (T-helper cells) are the "orchestrators" of the immune response, while CD8+ cells (T-cytotoxic cells) are the "effectors" that kill infected or cancerous cells. In a healthy immune system, T-helper cells predominate to maintain surveillance and coordinate various arms of the immune system (B-cells, macrophages, and CD8 cells). A ratio of 2:1 ensures an adequate supply of helper signals to maintain immune homeostasis. **2. Why other options are incorrect:** * **1:2 and 1:3:** These represent an **inverted ratio**. A ratio below 1.0 is a hallmark of significant immune dysfunction or viral suppression of the immune system. * **3:1:** While some healthy individuals may have higher ratios, 3:1 is above the standard reference range used in clinical examinations and medical textbooks. **Clinical Pearls for NEET-PG:** * **HIV/AIDS:** The most high-yield clinical application. HIV selectively infects and destroys CD4+ cells, leading to an **inverted CD4:CD8 ratio (<1.0)**. This inversion is a key marker for disease progression. * **Aging:** The ratio tends to decrease naturally with age (immunosenescence). * **Other causes of inversion:** Acute viral infections (like EBV/Infectious Mononucleosis), bone marrow transplants, and certain autoimmune diseases. * **Normal Absolute Count:** CD4 count is typically **500–1500 cells/mm³**. A count below **200 cells/mm³** defines the transition from HIV to AIDS.

Question 103: What is the minimum concentration of reduced hemoglobin required for cyanosis?

A. 1 gm/dl
B. 3 gm/dl
C. 7 gm/dl
D. 5 gm/dl (Correct Answer)

Explanation: **Explanation:** **The Underlying Concept:** Cyanosis is the bluish discoloration of the skin and mucous membranes. It occurs not because of a lack of oxygenated hemoglobin, but due to the absolute amount of **reduced (deoxygenated) hemoglobin** present in the capillaries. For cyanosis to be clinically detectable, the concentration of reduced hemoglobin must reach or exceed **5 gm/dl** in the capillary blood. **Why Option D is Correct:** The threshold of 5 gm/dl is a physiological constant. It is important to note that this refers to the *absolute* amount, not a percentage. This explains why anemic patients (with low total Hb) may not show cyanosis even when severely hypoxic, while polycythemic patients may show cyanosis even with mild hypoxia. **Why Other Options are Incorrect:** * **A (1 gm/dl) & B (3 gm/dl):** These concentrations are too low to cause the characteristic bluish hue visible through the skin. Normal arterial blood contains about 0.75 gm/dl of reduced Hb, which does not cause discoloration. * **C (7 gm/dl):** While a patient with 7 gm/dl of reduced Hb will certainly be cyanotic, this is well above the *minimum* threshold required for the initial clinical manifestation. **High-Yield Clinical Pearls for NEET-PG:** 1. **Anemia Paradox:** A severely anemic patient (e.g., Hb < 5 gm/dl) cannot develop cyanosis because they cannot reach the 5 gm/dl threshold of reduced Hb—they would likely die of hypoxia first. 2. **Polythemia:** Patients with high Hb levels develop cyanosis more easily. 3. **Central vs. Peripheral Cyanosis:** Central cyanosis (seen on the tongue/lips) indicates systemic arterial desaturation, whereas peripheral cyanosis (fingertips) often indicates slowed circulation (e.g., cold exposure, heart failure). 4. **Methemoglobinemia:** Cyanosis can occur with only **1.5 gm/dl** of methemoglobin, as it has a much darker pigment than reduced Hb.

Question 104: The conversion of prothrombin to thrombin requires a factor to participate along with calcium. Which factor is this?

A. Labile factor (Correct Answer)
B. Stable factor
C. Fibrin
D. Thromboplastin

Explanation: The conversion of prothrombin (Factor II) to thrombin (Factor IIa) is the final common pathway of the coagulation cascade. This process is mediated by the **Prothrombinase Complex**. ### 1. Why "Labile Factor" is Correct The Prothrombinase Complex consists of: * **Factor Xa** (The active enzyme) * **Factor Va** (The cofactor) * **Calcium ions** (Factor IV) * **Phospholipids** (from platelets) **Factor V** is historically known as the **Labile Factor** because its activity deteriorates rapidly in stored plasma. In the complex, Factor Va acts as a critical accelerator, increasing the reaction rate of prothrombin conversion by nearly 1,000-fold. Therefore, it is the factor that must participate alongside calcium and Factor Xa to produce thrombin. ### 2. Analysis of Incorrect Options * **B. Stable Factor (Factor VII):** This factor is part of the extrinsic pathway. It initiates coagulation by binding with Tissue Factor but does not directly convert prothrombin to thrombin. * **C. Fibrin (Factor Ia):** This is the end product of the coagulation cascade. Thrombin converts soluble fibrinogen into insoluble fibrin threads; fibrin does not catalyze thrombin formation. * **D. Thromboplastin (Factor III):** Also known as Tissue Factor, it initiates the extrinsic pathway. While it starts the cascade that leads to Factor X activation, it is not the immediate cofactor for prothrombin conversion. ### 3. NEET-PG Clinical Pearls * **Factor V Leiden:** A common genetic mutation causing resistance to activated Protein C, leading to a hypercoagulable state (thrombophilia). * **Vitamin K Dependency:** Factors **II, VII, IX, and X** (and Proteins C and S) are Vitamin K dependent. Factor V is **not** Vitamin K dependent. * **Common Pathway:** Remember the sequence **10 $\rightarrow$ 5 $\rightarrow$ 2 $\rightarrow$ 1** (Factors X, V, II, I).

Question 105: What substance is found in the secondary granules of neutrophils?

A. Lactoferrin (Correct Answer)
B. Proteolytic enzymes
C. Nucleotidase
D. Catalase

Explanation: **Explanation:** Neutrophils (Polymorphonuclear leukocytes) contain two main types of granules essential for their microbicidal activity: **Primary (Azurophilic)** and **Secondary (Specific)** granules. **1. Why Lactoferrin is Correct:** Secondary granules are the most numerous and contain substances that help in both bacteriostatic and bactericidal actions. **Lactoferrin** is a key protein found in these granules; it acts by sequestering free iron, which is essential for bacterial growth, thereby inhibiting microbial proliferation. Other contents of secondary granules include Vitamin B12-binding protein, Lysozyme, and Collagenase. **2. Analysis of Incorrect Options:** * **Proteolytic enzymes:** These (such as Elastase and Cathepsin G) are primarily found in **Primary (Azurophilic) granules**, which are essentially modified lysosomes. * **Nucleotidase:** Specifically, 5'-nucleotidase is a marker enzyme for the **plasma membrane** of cells, not the cytoplasmic granules of neutrophils. * **Catalase:** This enzyme is located within **Peroxisomes**. It plays a role in neutralizing hydrogen peroxide ($H_2O_2$) but is not a constituent of neutrophil secondary granules. **3. High-Yield Facts for NEET-PG:** * **Primary Granules (Azurophilic):** Contain **Myeloperoxidase (MPO)**, Acid hydrolases, Defensins, and Elastase. MPO is the most important marker for primary granules. * **Secondary Granules (Specific):** Contain **Lactoferrin**, Alkaline Phosphatase, and NADPH oxidase components. * **Tertiary Granules:** Contain Gelatinase and Cathepsins. * **Clinical Correlation:** In **Chediak-Higashi syndrome**, there is a defect in vesicle fusion leading to giant lysosomal granules, resulting in impaired chemotaxis and degranulation.

Question 106: Eosinophils secrete all of the following except?

A. Hydrolytic enzymes
B. Major basic protein
C. Reactive form of oxygen
D. Eosinophilic chemotactic factor (Correct Answer)

Explanation: ### Explanation The correct answer is **D. Eosinophilic chemotactic factor (ECF-A)**. The core concept to understand here is the difference between what a cell **secretes to kill pathogens** versus what **attracts the cell** to the site of inflammation. **1. Why Eosinophilic Chemotactic Factor is the correct answer:** Eosinophilic Chemotactic Factor (ECF-A) is **not** secreted by eosinophils; rather, it is primarily released by **mast cells and basophils** during degranulation. Its function is to act as a chemical "beacon" that recruits eosinophils to the site of an allergic reaction or parasitic infection. Eosinophils move toward this factor; they do not produce it. **2. Why the other options are incorrect:** Eosinophils are specialized granulocytes designed to kill large parasites (helminths). To do this, they secrete several potent substances: * **Major Basic Protein (MBP):** The most characteristic secretion of eosinophils. It is highly toxic to helminths and also triggers histamine release from mast cells. * **Hydrolytic Enzymes:** Eosinophils contain lysosomes filled with enzymes like acid phosphatase and nucleases to digest foreign material. * **Reactive Forms of Oxygen (ROS):** Like neutrophils, eosinophils undergo a "respiratory burst" to produce superoxide and hydrogen peroxide to kill pathogens. **High-Yield Clinical Pearls for NEET-PG:** * **Eosinophilia:** Defined as an absolute eosinophil count **>500/µL**. Common causes include **NAACP**: **N**eoplasia, **A**llergy/Asthma, **A**ddison’s disease, **C**onnective tissue disorders, and **P**arasites. * **Charcot-Leyden Crystals:** These are microscopic crystals found in the sputum of asthmatics, formed from the breakdown of eosinophil membrane proteins (Galectin-10). * **Eosinophil Peroxidase:** Distinct from myeloperoxidase (MPO) in neutrophils; it helps in the formation of hypohalous acids to destroy parasites.

Question 107: Plasma thromboplastin antecedent is:

A. Antihemophilic A factor
B. Antihemophilic B factor
C. Antihemophilic C factor (Correct Answer)
D. Antihemophilic F factor

Explanation: **Explanation:** The clotting cascade involves a series of plasma proteins (factors) that lead to the formation of a fibrin clot. **Plasma Thromboplastin Antecedent (PTA)** is the synonymous name for **Factor XI**. 1. **Why Option C is correct:** Factor XI is known as **Antihemophilic C factor**. It is a part of the intrinsic pathway of coagulation. A deficiency in Factor XI leads to **Hemophilia C** (Rosenthal syndrome). Unlike Hemophilia A and B, which are X-linked, Hemophilia C is an autosomal recessive disorder and is particularly common in the Ashkenazi Jewish population. 2. **Why other options are incorrect:** * **Option A (Antihemophilic A factor):** This refers to **Factor VIII**. Its deficiency causes Hemophilia A (Classic Hemophilia), the most common type of hemophilia. * **Option B (Antihemophilic B factor):** This refers to **Factor IX** (also known as Christmas Factor). Its deficiency causes Hemophilia B (Christmas Disease). * **Option D (Antihemophilic F factor):** This is not a standard medical term for any recognized clotting factor. **High-Yield Clinical Pearls for NEET-PG:** * **Factor I:** Fibrinogen * **Factor II:** Prothrombin * **Factor III:** Tissue Thromboplastin * **Factor IV:** Calcium ions (the only inorganic factor) * **Factor V:** Labile factor / Proaccelerin * **Factor VII:** Stable factor / Proconvertin * **Factor XII:** Hageman factor (initiates the intrinsic pathway *in vitro*) * **Factor XIII:** Fibrin-stabilizing factor (Laki-Lorand factor) * **Contact Activation:** Factors XII, XI, Prekallikrein, and High Molecular Weight Kininogen (HMWK) are known as the "Contact Factors."

Question 108: Which coagulation factor is not present in its active circulating form in the blood?

A. Factor XI
B. Factor X
C. Factor III (Correct Answer)
D. Factor XIII

Explanation: **Explanation:** The correct answer is **Factor III (Tissue Factor)**. **Why Factor III is the correct answer:** Coagulation factors are generally synthesized by the liver and circulate in the plasma as inactive zymogens. However, **Factor III (Tissue Factor/Thromboplastin)** is a high-molecular-weight glycoprotein that is **not** present in the circulating blood under physiological conditions. It is an integral membrane protein found in the subendothelial layers (adventitia of blood vessels) and extravascular tissues. It only comes into contact with blood following vascular injury, where it binds with Factor VIIa to initiate the **Extrinsic Pathway** of the coagulation cascade. **Analysis of Incorrect Options:** * **Factor XI (Plasma Thromboplastin Antecedent):** This is a zymogen that circulates in the blood in its inactive form and is part of the Intrinsic Pathway. * **Factor X (Stuart-Prower Factor):** This is a Vitamin K-dependent serine protease that circulates in the plasma. It is the first factor of the Common Pathway. * **Factor XIII (Fibrin Stabilizing Factor):** This circulates in the plasma (bound to fibrinogen) and is activated by thrombin to cross-link fibrin clots. **High-Yield Clinical Pearls for NEET-PG:** * **Factor IV** is Calcium (the only inorganic factor). * **Factor VI** does not exist (formerly thought to be activated Factor V). * **Labile Factor:** Factor V (activity declines in stored blood). * **Stable Factor:** Factor VII (shortest half-life among all factors). * **Contact Factors:** Factors XI, XII, Prekallikrein, and High Molecular Weight Kininogen (HMWK). * **Vitamin K Dependent Factors:** II, VII, IX, and X.

Question 109: A father has blood group B and the mother has blood group AB. Which of the following blood groups are the children NOT likely to have?

A. O (Correct Answer)
B. A
C. B
D. AB

Explanation: ### Explanation The inheritance of ABO blood groups is based on **Mendelian genetics** and the principle of **multiple alleles**. The ABO gene has three alleles: $I^A$, $I^B$, and $i$ (where $i$ is recessive). **1. Why Option A (O) is Correct:** To have blood group **O**, a child must have the genotype **$ii$**, receiving one '$i$' allele from each parent. * **Mother:** Blood group AB has the genotype **$I^A I^B$**. She does not possess the '$i$' allele. * **Father:** Blood group B can have the genotype **$I^B I^B$** (homozygous) or **$I^B i$** (heterozygous). Since the mother cannot contribute an '$i$' allele, it is genetically impossible for the offspring to have blood group O ($ii$). **2. Why Other Options are Incorrect:** * **Option B (A):** If the father is heterozygous ($I^B i$) and the mother provides the $I^A$ allele, the child can be $I^A i$ (Group A). * **Option C (B):** If the father provides $I^B$ and the mother provides $I^B$, the child will be $I^B I^B$ or $I^B i$ (Group B). * **Option D (AB):** If the father provides $I^B$ and the mother provides $I^A$, the child will be $I^A I^B$ (Group AB). **Clinical Pearls for NEET-PG:** * **Codominance:** Alleles A and B are codominant (both expressed in AB group). * **Bombay Phenotype:** A rare condition where a person lacks the H-antigen. They may phenotypically test as Group O even if they genetically possess A or B alleles. * **Universal Donor/Recipient:** O negative is the universal donor (no antigens); AB positive is the universal recipient (no antibodies). * **Bernstein’s Formula:** Used to calculate allele frequencies in a population ($p+q+r = 1$).

Question 110: Which factor is required for erythrocyte stability?

A. Ankyrin
B. Spectrin
C. NADPH
D. All of the above (Correct Answer)

Explanation: **Explanation:** Erythrocyte stability and survival depend on both **structural integrity** (the cytoskeleton) and **metabolic protection** (oxidative stress management). 1. **Structural Stability (Ankyrin & Spectrin):** The RBC membrane must be highly deformable to squeeze through narrow capillaries. This flexibility is provided by a protein network on the inner surface of the membrane. **Spectrin** is the primary cytoskeletal protein that forms a hexagonal meshwork. **Ankyrin** acts as the crucial "anchor," linking the spectrin network to the integral membrane protein (Band 3). Deficiencies in these proteins lead to membrane instability, resulting in conditions like **Hereditary Spherocytosis**. 2. **Metabolic Stability (NADPH):** Mature RBCs lack mitochondria and rely on the Hexose Monophosphate (HMP) Shunt to produce **NADPH**. NADPH is essential for maintaining a pool of reduced glutathione, which neutralizes reactive oxygen species (ROS). Without NADPH, hemoglobin denatures (forming Heinz bodies) and the cell membrane undergoes oxidative damage, leading to hemolysis. **Why "All of the above" is correct:** Stability is not just physical; it is biochemical. While Ankyrin and Spectrin provide the mechanical framework to prevent fragmentation, NADPH provides the chemical protection necessary to prevent premature destruction. **High-Yield Clinical Pearls for NEET-PG:** * **Hereditary Spherocytosis:** Most commonly due to a deficiency in **Ankyrin** (most frequent) or Spectrin. * **G6PD Deficiency:** The most common enzyme deficiency worldwide; it impairs **NADPH** production, leading to episodic hemolysis under oxidative stress. * **Vertical vs. Horizontal Interactions:** Defects in vertical interactions (Ankyrin/Band 3) cause Spherocytosis; defects in horizontal interactions (Spectrin dimers) cause **Hereditary Elliptocytosis**.

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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