Blood and Immunity — MCQs

Blood and Immunity Indian Medical PG Practice Questions and MCQs

Question 31: Factor IX is also known as:

A. Stuart factor
B. Christmas factor (Correct Answer)
C. Prothrombin
D. Fibrin factor

Explanation: **Explanation:** **Factor IX** is a vitamin K-dependent serine protease in the coagulation cascade. It is known as the **Christmas factor**, named after Stephen Christmas, the first patient diagnosed with its deficiency in 1952. Factor IX is a critical component of the **intrinsic pathway**; it works with its cofactor (Factor VIIIa) to activate Factor X. **Analysis of Options:** * **Option A (Stuart factor):** This refers to **Factor X**. It is the first factor of the **common pathway**, where the intrinsic and extrinsic pathways converge to eventually convert prothrombin to thrombin. * **Option C (Prothrombin):** This is **Factor II**. It is synthesized in the liver and converted into thrombin (IIa) by the prothrombinase complex (Xa, Va, Ca²⁺, and phospholipids). * **Option D (Fibrin factor):** This usually refers to **Factor I (Fibrinogen)**, which is the precursor to fibrin, the meshwork of a blood clot. **Clinical Pearls for NEET-PG:** 1. **Hemophilia B:** Deficiency of Factor IX is called Hemophilia B or **Christmas Disease**. It is an X-linked recessive disorder, clinically indistinguishable from Hemophilia A (Factor VIII deficiency). 2. **Vitamin K Dependence:** Factors **II, VII, IX, and X** (mnemonic: 1972) along with Protein C and S require Vitamin K for γ-carboxylation to become functional. 3. **Laboratory Marker:** Since Factor IX is part of the intrinsic pathway, its deficiency prolongs the **Activated Partial Thromboplastin Time (aPTT)**, while the Prothrombin Time (PT) remains normal.

Question 32: Which interleukin is secreted by Type I helper cells?

A. Interleukin-1
B. Interleukin-2 (Correct Answer)
C. Interleukin-4
D. Interleukin-5

Explanation: ### Explanation **Concept Overview:** Helper T-cells (CD4+) differentiate into two primary subsets, **Th1 (Type I)** and **Th2 (Type II)**, based on the cytokines they encounter and subsequently secrete. This distinction is crucial for determining the type of immune response (cellular vs. humoral). **Why Option B is Correct:** **Interleukin-2 (IL-2)** is a signature cytokine of **Th1 cells**. Th1 cells primarily drive **cell-mediated immunity**. They secrete IL-2 (which stimulates T-cell proliferation) and Interferon-gamma (IFN-γ), which activates macrophages and cytotoxic T-cells to fight intracellular pathogens like *M. tuberculosis*. **Analysis of Incorrect Options:** * **Option A (IL-1):** This is a pro-inflammatory cytokine primarily secreted by **macrophages** and antigen-presenting cells (APCs), not Th1 cells. It acts as an endogenous pyrogen. * **Option C (IL-4):** This is the hallmark cytokine of **Th2 cells**. It promotes B-cell differentiation into plasma cells and stimulates the class switching of antibodies to **IgE**. * **Option D (IL-5):** Also secreted by **Th2 cells**, IL-5 is responsible for the proliferation and activation of **eosinophils**, playing a key role in helminthic infections and allergic reactions. **NEET-PG High-Yield Pearls:** * **Th1 Mnemonic:** "1-2-G" (Th**1** secretes IL-**2** and IFN-**G**amma). * **Th2 Mnemonic:** "4, 5, 6, 10, 13" (Th2 cells secrete these interleukins; IL-4 and IL-5 are the most frequently tested). * **The "Switch":** IL-12 induces Th1 differentiation, while IL-4 induces Th2 differentiation. * **Clinical Link:** Lepromatous leprosy involves a Th2 response (ineffective), whereas Tuberculoid leprosy involves a Th1 response (effective clearance).

Question 33: All of the following occur in hemostasis except?

A. Vasospasm of blood vessel
B. Platelet plug formation
C. Dissolution of clot by plasmin (Correct Answer)
D. Formation of fibrin clot

Explanation: **Explanation:** Hemostasis is the physiological process that stops bleeding at the site of vascular injury. It is a protective mechanism designed to maintain blood in a fluid state within the vessels while being ready to form a solid plug rapidly upon injury. **Why Option C is the correct answer:** Dissolution of the clot by **plasmin** (Fibrinolysis) is the final stage of the overall process, but it is technically the **termination or reversal of hemostasis**, not a step in its formation. Hemostasis aims to create a clot to prevent blood loss; fibrinolysis occurs later to remove the clot once the vessel wall is repaired and to restore normal blood flow. **Analysis of other options:** * **A. Vasospasm:** This is the immediate **vascular phase** of hemostasis. Myogenic contraction and local autacoid factors (like Thromboxane A2) cause vasoconstriction to reduce blood flow to the injured area. * **B. Platelet plug formation:** Known as **Primary Hemostasis**, this involves platelet adhesion, activation, and aggregation to form a temporary, friable plug. * **D. Formation of fibrin clot:** Known as **Secondary Hemostasis**, this involves the coagulation cascade (intrinsic, extrinsic, and common pathways) which converts soluble fibrinogen into an insoluble fibrin mesh, stabilizing the platelet plug. **High-Yield Clinical Pearls for NEET-PG:** * **Sequence of Hemostasis:** Vasoconstriction → Primary Hemostasis (Platelet plug) → Secondary Hemostasis (Fibrin clot) → Clot Retraction → Fibrinolysis. * **Plasminogen Activator:** Tissue Plasminogen Activator (tPA) converts plasminogen to plasmin. This is the basis for "clot-buster" therapy in MI and Stroke. * **Vitamin K:** Necessary for the synthesis of factors II, VII, IX, and X. * **Antithrombin III:** The most important natural anticoagulant that inhibits thrombin.

Question 34: During which period does the hepatic stage of erythropoiesis occur?

A. First trimester of pregnancy
B. Second trimester of pregnancy (Correct Answer)
C. Perinatal period
D. Puberty

Explanation: ### Explanation Erythropoiesis (the production of red blood cells) occurs in distinct stages during intrauterine life, transitioning through different anatomical sites as the fetus develops. **1. Why Option B is Correct:** The **Hepatic Stage** is the primary phase of erythropoiesis during the **second trimester**. It begins around the 6th week of gestation, reaches its peak activity at the 4th–5th month, and significantly declines by the end of the second trimester as the bone marrow takes over. While the liver is the main organ, the spleen and lymph nodes also contribute minorly during this period. **2. Analysis of Incorrect Options:** * **Option A (First Trimester):** The earliest stage is the **Mesoblastic Stage**. It occurs in the **yolk sac** starting around the 3rd week of gestation. By the end of the first trimester, this phase is largely replaced by hepatic production. * **Option C (Perinatal Period):** By the third trimester and the perinatal period (around birth), the **Myeloid Stage** is dominant. The **bone marrow** becomes the primary site of erythropoiesis from the 5th–7th month onwards. * **Option D (Puberty):** In post-natal life and through puberty, erythropoiesis is confined exclusively to the red bone marrow of membranous bones (vertebrae, sternum, ribs, and ilia) and the proximal ends of long bones. **3. High-Yield Clinical Pearls for NEET-PG:** * **Sequence of Sites:** Yolk Sac (Mesoblastic) → Liver/Spleen (Hepatic) → Bone Marrow (Myeloid). * **Hemoglobin Types:** Yolk sac produces Gower-1, Gower-2, and Portland hemoglobins. The hepatic stage primarily produces **HbF (Fetal Hemoglobin)**. * **Extramedullary Hematopoiesis:** If the bone marrow fails in adults (e.g., Myelofibrosis or Thalassemia), the liver and spleen can resume blood cell production, a pathological reversal to the fetal hepatic stage.

Question 35: Which of the following is NOT a Vitamin K dependent clotting factor?

A. Factor II
B. Factor VII
C. Factor VIII (Correct Answer)
D. Factor IX

Explanation: **Explanation:** The synthesis of certain coagulation factors in the liver requires **Vitamin K** as a vital cofactor. Specifically, Vitamin K is necessary for the enzyme **gamma-glutamyl carboxylase**, which adds a carboxyl group to glutamate residues on these proteins. This carboxylation allows the factors to bind calcium ions ($Ca^{2+}$) and attach to phospholipid surfaces, a process essential for the clotting cascade. **Why Factor VIII is the correct answer:** **Factor VIII (Anti-hemophilic factor)** is NOT Vitamin K dependent. It is a glycoprotein cofactor synthesized primarily by sinusoidal endothelial cells in the liver and extrahepatic tissues. It circulates in the blood bound to **von Willebrand Factor (vWF)**, which protects it from rapid degradation. **Analysis of incorrect options:** * **Factor II (Prothrombin):** The precursor to thrombin; it is the most abundant Vitamin K-dependent serine protease. * **Factor VII (Stable Factor):** Part of the extrinsic pathway; it has the **shortest half-life** (approx. 6 hours) among all clotting factors. * **Factor IX (Christmas Factor):** Part of the intrinsic pathway; its deficiency leads to Hemophilia B. **High-Yield NEET-PG Pearls:** 1. **Mnemonic:** Remember the Vitamin K-dependent factors as **"1972"** (Factors **10, 9, 7, and 2**). 2. **Anticoagulant Proteins:** Protein **C** and Protein **S** are also Vitamin K-dependent. 3. **Warfarin Mechanism:** Warfarin inhibits **Vitamin K Epoxide Reductase (VKOR)**, preventing the recycling of Vitamin K and thus inhibiting the synthesis of these factors. 4. **Clinical Correlation:** In Vitamin K deficiency or Warfarin therapy, **Factor VII** is the first to decrease, making **Prothrombin Time (PT)** the earliest lab parameter to be prolonged.

Question 36: What antibodies are present in an individual with blood group O?

A. Anti-A antibody only
B. Anti-B antibody only
C. Both Anti-A and Anti-B antibodies (Correct Answer)
D. No antibodies

Explanation: ### Explanation **Concept Overview: Landsteiner’s Law** The presence of antibodies in the plasma is governed by **Landsteiner’s Law**, which states that if an agglutinogen (antigen) is absent on the red blood cell (RBC) membrane, the corresponding agglutinin (antibody) must be present in the plasma. In **Blood Group O**, the RBCs lack both Antigen A and Antigen B. According to Landsteiner’s Law, because both antigens are absent, the body produces antibodies against both. Therefore, the plasma contains **both Anti-A and Anti-B antibodies**. **Analysis of Options:** * **Option C (Correct):** Individuals with Group O have neither A nor B antigens, leading to the development of both Anti-A and Anti-B antibodies (predominantly of the IgG and IgM classes). * **Option A:** Anti-A only is found in individuals with **Blood Group B**. * **Option B:** Anti-B only is found in individuals with **Blood Group A**. * **Option D:** No antibodies are found in the plasma of individuals with **Blood Group AB**, as they possess both A and B antigens on their RBCs. **High-Yield Clinical Pearls for NEET-PG:** * **Universal Donor:** Group O is the universal donor because its RBCs lack A and B antigens, preventing a reaction with the recipient's antibodies. Specifically, **O Negative** is the preferred universal donor in emergencies. * **Antibody Nature:** Naturally occurring ABO antibodies are primarily **IgM** (cannot cross the placenta). However, in Group O individuals, Anti-A and Anti-B are often **IgG**, which can cross the placenta and cause Hemolytic Disease of the Newborn (HDN). * **H-Antigen:** Group O individuals have the maximum amount of **H-substance**, which is the precursor for A and B antigens. The rare **Bombay Phenotype** lacks even the H-antigen.

Question 37: Blood is not a Newtonian fluid because:

A. Its viscosity does not change with velocity.
B. Its viscosity changes with velocity. (Correct Answer)
C. Its density does not change with velocity.
D. Its density changes with velocity.

Explanation: **Explanation:** The classification of a fluid as **Newtonian** or **Non-Newtonian** depends on the relationship between shear stress and shear rate. 1. **Why the correct answer is right:** A Newtonian fluid (like water or plasma) maintains a constant viscosity regardless of the flow velocity or force applied. Blood, however, is a **Non-Newtonian fluid** because its viscosity is **inversely proportional** to its velocity (shear rate). This is primarily due to the presence of formed elements (RBCs). At low velocities, RBCs aggregate into stacks called **Rouleaux**, which increases internal friction and viscosity. As velocity increases, these aggregates break apart and RBCs undergo "deformability" (streamlining), which decreases viscosity. This specific behavior is known as **Pseudoplasticity** or "shear-thinning." 2. **Why the incorrect options are wrong:** * **Option A:** This describes a Newtonian fluid. If blood's viscosity did not change with velocity, it would be Newtonian. * **Options C & D:** Newtonian status is defined by **viscosity**, not density. While density is a physical property of blood, it does not dictate the rheological (flow) classification in this context. **High-Yield NEET-PG Pearls:** * **Fahraeus-Lindqvist Effect:** In very small blood vessels (capillaries <1.5mm), blood viscosity actually *decreases* because RBCs move to the center of the vessel (axial accumulation), leaving a cell-free plasma layer at the walls. * **Hematocrit:** This is the single most important determinant of blood viscosity. * **Temperature:** Viscosity increases as body temperature decreases (relevant in induced hypothermia or Raynaud’s phenomenon).

Question 38: Which of the following is not a secondary granule?

A. Lactoferrin
B. Alkaline phosphatase
C. BPI (Correct Answer)
D. Lysozyme

Explanation: ### Explanation In neutrophils (Polymorphonuclear leukocytes), granules are classified based on their contents and the timing of their appearance during granulopoiesis. **1. Why BPI is the Correct Answer:** **Bactericidal/Permeability-Increasing protein (BPI)** is a constituent of **Primary (Azurophilic) granules**, not secondary granules. Primary granules are the first to appear (at the promyelocyte stage) and contain potent antimicrobial agents like Myeloperoxidase (MPO), Defensins, BPI, and Neutral Proteases (Elastase, Cathepsin G). BPI specifically targets Gram-negative bacteria by binding to lipopolysaccharides (LPS). **2. Analysis of Incorrect Options (Secondary Granules):** Secondary (Specific) granules appear later (at the myelocyte stage) and contain markers used to identify mature neutrophils. * **Lactoferrin:** A key secondary granule protein that sequesters iron, preventing bacterial growth. * **Alkaline Phosphatase (NAP/ALP):** A classic marker for secondary granules. Its levels are clinically used to differentiate Leukemoid reactions (High NAP) from Chronic Myeloid Leukemia (Low NAP). * **Lysozyme:** Found in **both** primary and secondary granules. Since it is a major component of secondary granules, it is not the "odd one out" compared to BPI, which is strictly primary. **3. High-Yield Clinical Pearls for NEET-PG:** * **Primary Granule Marker:** Myeloperoxidase (MPO). * **Secondary Granule Marker:** Lactoferrin and Vitamin B12-binding protein. * **Tertiary Granules:** Contain Gelatinase and Cathepsins; they are involved in tissue degradation and migration. * **Chediak-Higashi Syndrome:** Characterized by giant lysosomal granules due to a defect in vesicle trafficking (LYST gene). * **Specific Granule Deficiency:** A rare condition leading to recurrent pyogenic infections due to the absence of secondary granules.

Question 39: What is the Rh factor?

A. IgM antibody (Correct Answer)
B. Mucopolysaccharide
C. IgG antibody
D. Fatty acid

Explanation: **Explanation:** The **Rh factor** (specifically the D antigen) is a protein found on the surface of red blood cells. However, in the context of clinical immunology and blood banking, the term "Rh factor" is also historically associated with the **Rheumatoid Factor (RF)** in some older medical nomenclature, though they are distinct entities. In the context of this specific question, the "Rh factor" refers to **Rheumatoid Factor**, which is an autoantibody. 1. **Why A is correct:** Rheumatoid Factor is classically an **IgM antibody** directed against the Fc portion of the patient's own IgG. It is a key diagnostic marker for Rheumatoid Arthritis. 2. **Why B is incorrect:** Mucopolysaccharides (glycosaminoglycans) are carbohydrate chains found in connective tissues; they do not constitute antibodies or blood group antigens. 3. **Why C is incorrect:** While RF can occasionally be IgG or IgA, the **standard diagnostic "Rh factor" is IgM**. Note: Do not confuse this with *anti-D antibodies* (formed during Rh sensitization in pregnancy), which are indeed IgG and can cross the placenta. 4. **Why D is incorrect:** Fatty acids are components of lipids and have no structural relationship to immune globulins or surface antigens. **High-Yield Clinical Pearls for NEET-PG:** * **Rh Blood Group:** The D antigen is the most immunogenic. Anti-D antibodies are **IgG** (warm antibodies), which is why they cause Hemolytic Disease of the Newborn (HDN). * **Rheumatoid Factor (RF):** It is an **IgM against the Fc fragment of IgG**. It is found in 70-80% of RA patients but is not pathognomonic (also seen in SLE, Sjögren's, and chronic infections). * **Rose-Waaler Test:** A classic hemagglutination test used to detect Rheumatoid Factor.

Question 40: Blood platelets in stored blood do not remain functional after how many hours?

A. 24 (Correct Answer)
B. 48
C. 72
D. 96

Explanation: **Explanation:** The functionality of blood components in stored whole blood depends heavily on the storage temperature and the specific metabolic requirements of the cells. **1. Why Option A (24 hours) is correct:** When whole blood is stored at the standard refrigeration temperature of **4°C (2-6°C)**, platelets undergo a rapid loss of viability and functional integrity. Within **24 hours**, platelets lose their ability to aggregate and form a primary hemostatic plug. This is primarily due to "cold-induced activation" and metabolic changes that occur at low temperatures, which differ from the optimal storage conditions for isolated platelets (which require room temperature with constant agitation). Therefore, if a patient requires functional platelets, stored whole blood older than 24 hours is ineffective. **2. Why other options are incorrect:** * **Options B, C, and D (48, 72, 96 hours):** By these time points, the platelet count may still be detectable in the bag, but the cells are functionally inert. Labile coagulation factors (Factor V and VIII) also begin to decline significantly after 24–48 hours in stored blood. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Platelet Concentrates:** Unlike whole blood, isolated platelet concentrates are stored at **20-24°C (Room Temperature)** with continuous agitation. In these conditions, they remain functional for **5 days**. * **Storage Lesion:** This term refers to the biochemical and morphological changes in stored blood (e.g., decrease in 2,3-DPG, decrease in pH, and increase in extracellular Potassium). * **Fresh Whole Blood:** Defined as blood stored for less than 24 hours; it is the only source of functional platelets and labile factors in whole blood form. * **Factor Stability:** Factor VIII is the most labile; it loses about 50% of its activity within 24 hours of storage at 4°C.

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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