Blood and Immunity — MCQs

Blood and Immunity Indian Medical PG Practice Questions and MCQs

Question 451: Nude mice are not resistant to xenografts due to absence of

A. B cell
B. T cell (Correct Answer)
C. Absence of both B and T cells
D. Presence of both B and T cells

Explanation: ***T cell*** - Nude mice have a **congenital athymia**, meaning they lack a functional **thymus**. - The thymus is essential for the maturation and development of **T lymphocytes**, making these mice severely **T-cell deficient**. - Without functional T cells, nude mice cannot reject **xenografts** (tissue transplanted from a different species). *B cell* - While nude mice have impaired T-cell function, their **B-cell development and function remain largely intact**. - B cells develop in the **bone marrow** and do not require the thymus for maturation. - B cells alone are insufficient to reject xenografts, as this requires cell-mediated immunity. *Absence of both B and T cells* - This statement is incorrect because nude mice **do possess B cells**, even if their T-cell immunity is severely compromised. - The primary defect is in the **thymus**, affecting T-cell maturation, not B cells. - Complete absence of both would describe **SCID mice**, not nude mice. *Presence of both B and T cells* - This is incorrect as nude mice clearly have a **severe deficiency in T cells** due to athymia. - Their inability to reject xenografts is directly linked to this lack of functional T-cell immunity. - If both were present and functional, the mice would reject xenografts normally.

Question 452: Increase in plasma viscosity is maximally caused by which plasma protein?

A. Albumin
B. All have equal effect
C. Globulin
D. Fibrinogen (Correct Answer)

Explanation: ***Globulin*** - Increased levels of **globulin** proteins, particularly in inflammatory or proliferative conditions, have a significant impact on plasma viscosity due to their **high molecular weight** [1]. - **Globulins** contribute to **hyperviscosity syndrome**, which can lead to clinical symptoms like fatigue and visual disturbances [1]. *Albumin* - While **albumin** is the most abundant plasma protein, its primary role is in maintaining **oncotic pressure**, not significantly affecting plasma viscosity. - An increase in albumin does not correlate with plasma viscosity increases to the extent seen with globulins. *All have equal effect* - Different plasma proteins do not have **equal effects** on viscosity; **globulins** and **fibrinogen** particularly influence it more than **albumin**. - The impact on viscosity varies significantly with protein concentration and type, making this statement inaccurate. *Fibrinogen* - **Fibrinogen** does contribute to plasma viscosity but is typically less than that caused by globulins, especially when globulin levels are markedly elevated. - Its effect is more pronounced during **coagulation**, rather than in the general increase of plasma viscosity associated with inflammatory states. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 141-142.

Question 453: Chemotaxis is mediated by-

A. Histamine
B. Leukotriene C4 and C3a
C. Bradykinin
D. Leukotriene B4 and C5a (Correct Answer)

Explanation: ***Leukotriene B4 and C5a*** - Both **Leukotriene B4** [2] and **C5a** [1] are potent **chemoattractants** that guide the migration of neutrophils and other immune cells to sites of inflammation. - They are crucial in amplifying the **immune response**, particularly during acute inflammatory reactions. *Histamine* - Primarily involved in **vasodilation** and increased **vascular permeability**, rather than mediating chemotaxis. - Does not specifically attract immune cells to sites of injury or infection like leukotrienes do. *Bradykinin* - Mainly functions in **pain sensation** and promoting **vascular permeability**, not as a direct chemotactic agent. - It influences inflammation but does not effectively recruit immune cells to tissues. *Leukotriene C4 and C3a* - **Leukotriene C4** is involved in bronchoconstriction, while **C3a** [1] has roles in the complement system but is less potent than C5a in chemotaxis. - These mediators have different primary roles in inflammation, lacking the specificity of B4 and C5a for leukocyte attraction. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 99-100. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 95-96.

Question 454: What is the average size of platelets in micrometers?

A. 4-5 µm
B. 3-4 µm
C. 2-3 µm (Correct Answer)
D. 1-2 µm

Explanation: ***2-3 µm*** - Platelets, also known as **thrombocytes**, are small, anucleated cell fragments crucial for **hemostasis**, and their average diameter generally falls within the range of 2-3 micrometers. - This **small size** allows them to easily navigate through capillaries and aggregate rapidly at sites of vascular injury. *3-4 µm* - While platelets can vary slightly in size, an average of 3-4 µm is generally considered a bit on the larger side and not the typical average diameter. - Larger platelets might be seen in certain conditions like **idiopathic thrombocytopenic purpura (ITP)**, but this is not the average normal size. *4-5 µm* - This range is significantly larger than the typical size of normal circulating platelets. - Platelets this large would be considered **macroplatelets** and could indicate specific pathological conditions or inherited platelet disorders. *1-2 µm* - This size range is generally considered smaller than the average normal platelet size. - Very small platelets might be seen in some specific conditions, but it's not the usual average for healthy individuals.

Question 455: Interleukin responsible for Pyrexia is:

A. IL1 (Correct Answer)
B. IL4
C. IL3
D. IL8

Explanation: ***IL1*** - **Interleukin-1 (IL-1)** is a primary **endogenous pyrogen**, directly acting on the thermoregulatory center in the hypothalamus to induce fever. - It stimulates the production of **prostaglandin E2 (PGE2)**, which then alters the hypothalamic set point, leading to increased body temperature. *IL3* - **Interleukin-3 (IL-3)** is a **hematopoietic growth factor** that primarily stimulates the proliferation and differentiation of hematopoietic stem cells. - Its main role is in the development of various blood cell lineages, not directly in inducing fever. *IL4* - **Interleukin-4 (IL-4)** is a key cytokine in **allergic reactions** and **Th2 immune responses**, promoting B cell activation and IgE production. - It does not directly cause pyrexia; its primary functions are related to humoral immunity and immune regulation. *IL8* - **Interleukin-8 (IL-8)**, also known as **CXCL8**, is a potent **chemotactic factor** for neutrophils and other immune cells. - Its main function is to recruit inflammatory cells to sites of infection or injury, not to induce fever directly.

Question 456: Which protein primarily contributes to oncotic pressure in the blood?

A. Albumin (Correct Answer)
B. Globulins
C. Fibrinogen
D. Transferrin

Explanation: ***Albumin*** - **Albumin** is the most abundant plasma protein and its small size and high concentration make it the primary determinant of **oncotic pressure** in the blood. - Its presence in the capillaries draws water from the **interstitial space** back into the blood vessels, maintaining **fluid balance** and blood volume. *Fibrinogen* - **Fibrinogen** is a crucial protein involved in **blood clotting**, where it is converted into **fibrin** to form a clot. - While a plasma protein, its contribution to **oncotic pressure** is minor compared to albumin, as it's less abundant and larger in size. *Globulins* - **Globulins** are a diverse group of proteins involved in immune function (**immunoglobulins**), transport (e.g., **alpha** and **beta globulins**), and clotting. - While they contribute to total plasma protein concentration, their collective impact on **oncotic pressure** is secondary to that of albumin due to lower concentrations and varied molecular weights. *Transferrin* - **Transferrin** is a specific **beta-globulin** that plays a vital role in **iron transport** in the blood. - Its primary function is not related to **oncotic pressure**, and its concentration is significantly lower than albumin.

Question 457: The major role of 2,3-bisphosphoglycerate in RBCs is -

A. Acid-base balance
B. Reversal of glycolysis
C. Release of oxygen (Correct Answer)
D. Binding of oxygen

Explanation: ***Release of oxygen*** - **2,3-bisphosphoglycerate (2,3-BPG)** binds allosterically to **deoxyhemoglobin**, stabilizing its T (tense) state. - This binding reduces hemoglobin's affinity for oxygen, promoting the **release of oxygen** to tissues. *Acid-base balance* - While red blood cells play a role in **acid-base balance** through the bicarbonate buffer system, 2,3-BPG's primary role is not buffering. - The **chloride shift** and **carbonic anhydrase** are more directly involved in RBC acid-base regulation. *Reversal of glycolysis* - 2,3-BPG is an intermediate of the **Rapoport-Luebering shunt**, a side pathway of glycolysis. - It does not reverse glycolysis but rather is produced during glycolysis to serve a specific function in oxygen transport. *Binding of oxygen* - 2,3-BPG **decreases** hemoglobin's affinity for oxygen, thus promoting its *release* from hemoglobin, not its binding. - Oxygen binding to hemoglobin occurs primarily at the **heme iron** without 2,3-BPG.

Question 458: What is Proaccelerin?

A. Factor VII
B. Factor II
C. Factor V (Correct Answer)
D. Factor X

Explanation: ***Factor V*** - **Factor V**, also known as **proaccelerin** or **labile factor**, is a **plasma protein** that plays a crucial role in the coagulation cascade. - It is activated by thrombin to **Factor Va**, which then combines with Factor Xa, calcium, and phospholipid to form the **prothrombinase complex**, significantly enhancing thrombin generation. *Factor II* - **Factor II** is **prothrombin**, a precursor to **thrombin**, which is central to coagulation. - It is not referred to as preaccelerin. *Factor VII* - **Factor VII** is primarily involved in the **extrinsic pathway** of coagulation, becoming activated to Factor VIIa upon contact with tissue factor. - It works to activate Factor IX and Factor X, but it is not preaccelerin. *Factor X* - **Factor X**, also known as **Stuart-Prower factor**, is a key enzyme in the **common pathway** of coagulation, converting prothrombin to thrombin. - It is distinct from Factor V, which acts as a cofactor.

Question 459: Which of the following statements is TRUE regarding the Bohr effect?

A. Decreased affinity of Hb to O2 is associated with increased pH & decreased CO2
B. Decreased affinity of Hb to O2 is associated with increased pH & CO2
C. Decreased affinity of Hb to O2 is associated with decreased pH & increased CO2 (Correct Answer)
D. Decreased affinity of Hb to O2 is associated with decreased pH & decreased CO2

Explanation: ***Decreased affinity of Hb to O2 is associated with decreased pH & increased CO2*** - The **Bohr effect** describes how **hemoglobin's (Hb) affinity for oxygen (O2) decreases** in the presence of increased **acidity (decreased pH)** and higher **carbon dioxide (CO2)** concentrations. - This physiological adaptation ensures that O2 is **released more readily** to tissues that are actively metabolizing (e.g., muscle during exercise), as these tissues produce more CO2 and lactic acid, leading to a drop in pH. *Decreased affinity of Hb to O2 is associated with increased pH & decreased CO2* - An **increased pH** (more alkaline) and **decreased CO2** actually **increase Hb's affinity for O2**, shifting the oxygen dissociation curve to the left. - This scenario promotes **oxygen loading** onto hemoglobin, typically occurring in the lungs rather than O2 release in the tissues. *Decreased affinity of Hb to O2 is associated with increased pH & CO2* - This statement combines an **increased pH** (which increases Hb-O2 affinity) with **increased CO2** (which decreases Hb-O2 affinity), leading to a contradictory and incorrect physiological effect based on the Bohr principle. - The net effect of an increased pH would typically dominate in terms of O2 binding. *Decreased affinity of Hb to O2 is associated with decreased pH & decreased CO2* - While **decreased pH** does reduce Hb's affinity for O2, **decreased CO2** would tend to increase it. - Therefore, this combination does not accurately represent the primary conditions that lead to a significant decrease in Hb-O2 affinity as described by the Bohr effect in active tissues.

Question 460: Which immunoglobulin is primarily secreted by the intestine?

A. IgG
B. IgM
C. IgA (Correct Answer)
D. IgD

Explanation: **IgA** - **Secretory IgA** is the dominant immunoglobulin in mucosal secretions, including those of the intestine. - It plays a crucial role in providing **local immunity** by preventing microbial adherence and neutralizing toxins on mucosal surfaces. *IgG* - **IgG** is the most abundant immunoglobulin in serum and plays a major role in systemic immunity, including opsonization and complement activation. - While some IgG is found in secretions, it is not the primary immunoglobulin secreted by the intestine. *IgM* - **IgM** is a pentameric immunoglobulin, primarily found in blood and lymph, where it is very effective in activating the complement system and agglutinating antigens. - Although it can be found at mucosal surfaces in small amounts, it is not the principal secreted antibody in the intestine. *IgD* - **IgD** is primarily found on the surface of naive B lymphocytes, where it functions as a B cell receptor. - Its role in secreted form is minimal, and it is not significantly secreted into the intestine or other bodily fluids.

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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