Blood and Immunity Practice Questions

Q: A left shift in the Arneth index indicates which of the following?

Neutrophilia. **Explanation:** The **Arneth Index** (or Arneth count) is a classification of neutrophils based on the number of lobes in their nuclei. Normally, a mature neutrophil has 2 to 5 lobes. 1. **Why Neutrophilia is correct:** A **"Shift to the Left"** occurs when the bone marrow releases immature neutrophils (band cells or those with fewer than 3 lobes) into the circulation to meet an increased demand, typically during acute bacterial infections or inflammation. This rapid release results in a higher percentage of young cells, leading to **neutrophilia**. 2. **Why other options are incorrect:** * **Anemia:** Relates to red blood cell deficiency, not leukocyte nuclear morphology. * **Splenomegaly:** While the spleen filters blood, it does not directly dictate the nuclear lobulation of circulating neutrophils. * **Hyperactive bone marrow:** While a left shift implies increased production, the term is too broad. Specifically, a left shift is a hallmark of the *myeloid* response (neutrophilia), whereas "hyperactive marrow" could refer to erythroid or megakaryocytic hyperplasia. **High-Yield Clinical Pearls for NEET-PG:** * **Shift to the Right:** An increase in mature neutrophils with more than 5 lobes (hypersegmented neutrophils). This is a classic finding in **Megaloblastic Anemia** (Vitamin B12 or Folate deficiency). * **Normal Arneth Count:** * Stage I (1 lobe): 5% * Stage II (2 lobes): 35% * Stage III (3 lobes): 41% (Most common) * Stage IV (4 lobes): 17% * Stage V (5 lobes): 2% * **Cooke’s Criterion:** A similar classification used to identify megaloblastic changes.

Q: Fetal hemoglobin contains which of the following globin chains?

alpha 2, gamma 2. **Explanation:** **1. Why Option C is Correct:** Fetal hemoglobin (**HbF**) is the primary oxygen-transport protein in the human fetus during the last seven months of development in utero. It is composed of two **alpha (α)** chains and two **gamma (γ)** chains (**α₂γ₂**). The presence of gamma chains is physiologically significant because they lack the binding site for 2,3-Bisphosphoglycerate (2,3-BPG). This results in HbF having a **higher affinity for oxygen** than adult hemoglobin (HbA), allowing the fetus to effectively extract oxygen from maternal blood across the placenta. **2. Why Other Options are Incorrect:** * **Option A (α₂β₂):** This represents **Hemoglobin A (HbA)**, the major form of adult hemoglobin (approx. 97%). It replaces HbF shortly after birth. * **Option B (α₂δ₂):** This represents **Hemoglobin A₂ (HbA₂)**, a minor component of adult hemoglobin (approx. 2-3%). Elevated levels are often seen in Beta-thalassemia trait. **3. NEET-PG High-Yield Clinical Pearls:** * **HbF Switch:** Synthesis of HbF begins to decline at 30 weeks of gestation, and by 6 months of age, it is largely replaced by HbA. * **Oxygen Dissociation Curve:** Due to its high oxygen affinity, the curve for HbF is **shifted to the left** compared to HbA. * **Sickle Cell Anemia:** Hydroxyurea is used in treatment because it increases the production of HbF, which inhibits the polymerization of HbS. * **Embryonic Hemoglobins:** Before HbF, the embryo produces Gower 1 (ζ₂ε₂), Gower 2 (α₂ε₂), and Portland (ζ₂γ₂).

Q: Which of the following statements about TXA2 is incorrect?

It has platelet anti-aggregatory activity.. Thromboxane A2 (TXA2) is a potent eicosanoid derived from arachidonic acid that plays a central role in hemostasis. **1. Why Option D is the Correct Answer (The Incorrect Statement):** TXA2 is a powerful **platelet aggregator**, not an anti-aggregatory agent [4]. It acts via the TP receptor (Gq-coupled) to increase intracellular calcium, leading to the activation of the GPIIb/IIIa receptor, which facilitates platelet-to-platelet binding via fibrinogen [4]. It also acts as a potent **vasoconstrictor**. **2. Analysis of Incorrect Options (Correct Statements):** * **Option A:** TXA2 is primarily synthesized in **platelets** by the enzyme Thromboxane Synthase [2]. * **Option B:** The biosynthetic pathway involves the conversion of Arachidonic acid to cyclic endoperoxides (**PGG2 and PGH2**) by the enzyme Cyclooxygenase (COX-1) [1]. These endoperoxides are then converted into TXA2. * **Option C:** Because it promotes both platelet aggregation and vasoconstriction, TXA2 is fundamentally **prothrombotic**, aiding in the formation of a stable blood clot. **Clinical Pearls for NEET-PG:** * **Aspirin’s Mechanism:** Low-dose Aspirin irreversibly inhibits **COX-1** in platelets [1]. Since platelets are anuclear and cannot synthesize new enzymes, TXA2 production is inhibited for the lifetime of the platelet (7–10 days) [2]. * **The Balance:** While platelets produce TXA2 (pro-aggregatory), vascular endothelial cells produce **PGI2 (Prostacyclin)**, which is a potent vasodilator and **anti-aggregatory** agent [3]. The balance between these two determines vascular patency. * **TXA2 vs. PGI2:** Remember "TXA2 = **T**hrombosis" and "PGI2 = **I**nhibits aggregation."

Q: Platelets are derived from which of the following cell types?

Megakaryocytes. **Explanation:** **Correct Answer: A. Megakaryocytes** Platelets (thrombocytes) are not whole cells but are small, discoid, anucleated fragments of cytoplasm. They are derived from **Megakaryocytes**, which are the largest cells in the bone marrow. This process, known as **thrombopoiesis**, occurs when the cytoplasm of a mature megakaryocyte forms long, branching processes called **proplatelets**. These proplatelets extend into the marrow sinusoids and fragment into individual platelets under the influence of the hormone **Thrombopoietin** (primarily produced in the liver). **Why the other options are incorrect:** * **B. Lymphocytes:** These are agranulocytic white blood cells (B-cells, T-cells, NK cells) involved in adaptive immunity. They originate from lymphoid stem cells. * **C. Neutrophils:** These are granulocytes derived from the myeloid lineage (specifically myeloblasts). They are the primary cells involved in acute inflammation and phagocytosis. * **D. Plasma cells:** These are fully differentiated B-lymphocytes that specialize in secreting large quantities of antibodies (immunoglobulins). **High-Yield Facts for NEET-PG:** * **Normal Platelet Count:** 1.5 to 4.5 lakh/mm³. * **Lifespan:** Platelets circulate for approximately **7–10 days** and are primarily sequestered/destroyed in the **spleen**. * **Key Organelle:** Platelets contain **Alpha granules** (containing clotting factors like Fibrinogen and vWF) and **Dense granules** (containing ADP, ATP, Serotonin, and Calcium). * **Clinical Correlation:** **Thrombopoietin** levels are inversely regulated by the platelet mass; low platelets lead to higher free thrombopoietin, stimulating megakaryocyte production.

Q: Lysozyme is present in all secretions except which of the following?

Sweat. **Explanation:** **Lysozyme** (also known as muramidase) is a key component of the innate immune system. It functions as an antibacterial enzyme by hydrolyzing the β-1,4-glycosidic bonds between N-acetylmuramic acid and N-acetylglucosamine in the peptidoglycan layer of bacterial cell walls, primarily targeting Gram-positive bacteria. **Why Sweat is the Correct Answer:** Lysozyme is widely distributed in various exocrine secretions and mucosal surfaces to prevent infection. However, it is notably **absent in sweat**. The primary antimicrobial defense in sweat is not lysozyme, but rather **Dermcidin**, an antimicrobial peptide (AMP) secreted by eccrine sweat glands that exhibits broad-spectrum activity against bacteria and fungi. **Analysis of Incorrect Options:** * **Egg White:** This is one of the richest sources of lysozyme (historically called "avidin" or "G1 albumin"). It serves to protect the developing embryo from microbial invasion. * **Tears:** Secreted by the lacrimal glands, tears contain high concentrations of lysozyme to protect the cornea and conjunctiva from ocular infections. * **Saliva:** Lysozyme is a major non-antibody protective factor in saliva, working alongside lactoferrin and salivary peroxidase to maintain oral hygiene. **High-Yield NEET-PG Pearls:** * **Source:** In the blood, lysozyme is primarily derived from **neutrophils** (stored in specific/secondary granules) and **monocytes/macrophages**. * **Clinical Marker:** Elevated serum or urinary lysozyme levels are a diagnostic marker for **Acute Myelomonocytic Leukemia (AML-M4)** and **Acute Monocytic Leukemia (AML-M5)**. * **Paneth Cells:** In the gastrointestinal tract, lysozyme is secreted by Paneth cells located at the base of the Crypts of Lieberkühn.

Q: Which of the following cytokines is NOT a hematopoietin?

IL-8. ### 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).

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

2:1. **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.

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

5 gm/dl. **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.

Q: Which of the following is a characteristic function of plasma cells?

Helps in the formation of antibody. ### Explanation **Plasma cells** are specialized immune cells that represent the final stage of B-cell differentiation. Their primary function is the synthesis and secretion of large quantities of **antibodies (immunoglobulins)** into the blood and lymph to provide humoral immunity [2]. #### Why Option B is Correct: Upon exposure to an antigen, B-lymphocytes undergo clonal expansion and differentiate into plasma cells [1]. These cells act as "antibody factories," possessing an extensive network of **Rough Endoplasmic Reticulum (RER)** to facilitate high-volume protein (antibody) synthesis. #### Analysis of Incorrect Options: * **Option A (Contain a nucleus):** While plasma cells do contain a nucleus, this is a general feature of almost all eukaryotic cells and not a *characteristic function*. The nucleus is typically eccentric with a "cartwheel" or "clock-face" appearance due to heterochromatin distribution. * **Option C (Are deficient in cytoplasm):** This is incorrect. Plasma cells have **abundant basophilic cytoplasm** due to the high density of ribosomes and RER required for protein synthesis. They also feature a prominent "perinuclear halo," which represents the Golgi apparatus. * **Option D (Are derived from T cells):** Plasma cells are derived exclusively from **B-lymphocytes**, not T-lymphocytes [1]. #### NEET-PG High-Yield Pearls: * **Histology:** Look for the **"Cartwheel nucleus"** and **"Perinuclear Hof"** (clear zone near the nucleus representing the Golgi). * **Russell Bodies:** These are eosinophilic inclusions found in the cytoplasm of plasma cells, representing accumulated immunoglobulins. * **Clinical Correlation:** **Multiple Myeloma** is a plasma cell dyscrasia characterized by the malignant proliferation of a single clone of plasma cells, often identified by a "M-spike" on serum protein electrophoresis.

Question 1

What is the effect of sodium fluoride on the oxygen dissociation curve?

Accepted Answer

No effect on curve

Answer

Right shift

Answer

Left shift

Answer

Initial right and then left shift

Question 2

A left shift in the Arneth index indicates which of the following?

Accepted Answer

Neutrophilia

Answer

Anemia

Answer

Splenomegaly

Answer

Hyperactive bone marrow

Question 3

Fetal hemoglobin contains which of the following globin chains?

Accepted Answer

alpha 2, gamma 2

Answer

alpha 2, beta 2

Answer

alpha 2, delta 2

Answer

None of the above

Question 4

Which of the following statements about TXA2 is incorrect?

Accepted Answer

It has platelet anti-aggregatory activity.

Answer

It is formed in platelets.

Answer

It is formed from PGG2/H2.

Answer

It is prothrombotic.

Question 5

Platelets are derived from which of the following cell types?

Accepted Answer

Megakaryocytes

Answer

Lymphocytes

Answer

Neutrophils

Answer

Plasma cells

Question 6

Lysozyme is present in all secretions except which of the following?

Accepted Answer

Sweat

Answer

Egg white

Answer

Tears

Answer

Saliva

Question 7

Which of the following cytokines is NOT a hematopoietin?

Accepted Answer

IL-8

Answer

IL-2

Answer

IL-4

Answer

IL-7

Question 8

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

Accepted Answer

2:1

Answer

1:2

Answer

3:1

Answer

1:3

Question 9

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

Accepted Answer

5 gm/dl

Answer

1 gm/dl

Answer

3 gm/dl

Answer

7 gm/dl

Question 10

Which of the following is a characteristic function of plasma cells?

Accepted Answer

Helps in the formation of antibody

Answer

Contain a nucleus

Answer

Are deficient in cytoplasm

Answer

Are derived from T cells

Blood and Immunity — MCQs

Blood and Immunity — MCQs

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