Immunological Memory and Tolerance — MCQs
Which of the following statements about the secondary immune response is false?
Which of the following is a specific feature of acquired immunity?
Cell surface molecules involved in peripheral tolerance induction are
All are true regarding the development of T-cells, except?
Which of the following statements regarding rejection of solid organ transplants is true?
What is the inheritance pattern of the ABO blood group system and the HLA system?
All of the following are functions of the spleen EXCEPT?
What is the first cell in the development of red blood cells?
The biconcave shape of RBC is useful for all the following functions EXCEPT:
Which of the following is responsible for the adhesion of platelets to the vessel wall?
Immunological Memory and Tolerance Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following statements about the secondary immune response is false?
- A. The lag period is absent or significantly shorter.
- B. There is a negative phase in the response.
- C. Only T-dependent antigens are recognized.
- D. Immune response against a subsequent antigenic challenge is absent. (Correct Answer)
Explanation: ***Immune response against a subsequent antigenic challenge is absent.*** - This statement is **false** because the secondary immune response is characterized by a **much stronger and faster** immune response upon subsequent exposure to the same antigen. - The presence of **memory cells** ensures that the immune system is highly prepared to combat the antigen more efficiently than during the primary response. *The lag period is absent or significantly shorter.* - This statement is **true** for the secondary immune response. The **memory B and T cells** can be rapidly activated, reducing the time needed to mount an effective response. - Unlike primary responses that can take 5-10 days to produce antibodies, secondary responses typically produce antibodies within **1-3 days**. *There is a negative phase in the response.* - This statement is **false** for the secondary immune response. The **negative phase** is characteristic of the **primary immune response**, not the secondary response. - The negative phase in primary response refers to a transient drop in antibody concentration after initial antigen exposure due to antigen-antibody complex formation. However, the **secondary response shows immediate and robust antibody production** without this negative phase due to pre-existing memory cells. - While this statement is technically false, the question asks for THE false statement, and Option D is more obviously and fundamentally false. *Only T-dependent antigens are recognized.* - This statement is **partially false** but has some truth in context. While **T-dependent antigens** generate the most robust secondary responses with strong memory cell formation, the immune system doesn't ONLY recognize T-dependent antigens. - **T-independent antigens** can elicit responses but typically generate weaker, shorter-lived immunity without strong memory formation. The classical, robust secondary immune response with anamnestic features is predominantly associated with T-dependent antigens.
Question 2: Which of the following is a specific feature of acquired immunity?
- A. Immunological memory (Correct Answer)
- B. Affected by genetic makeup
- C. No antigen exposure
- D. Immediate response
Explanation: ***Immunological memory*** - A key characteristic of **acquired immunity** is the ability to "remember" previous encounters with specific pathogens. - This memory leads to a more rapid and robust immune response upon subsequent exposure to the same pathogen. - This is the **defining feature** that distinguishes acquired immunity from innate immunity. *Affected by genetic makeup* - While genetic makeup can influence the *efficiency* of the acquired immune system, it is not a **specific feature** that distinguishes it from innate immunity. - **Both innate and acquired immunity** are affected by genetic factors, determining baseline resistance and immune response capability. *No antigen exposure* - **Acquired immunity** is specifically characterized by its *dependence* on antigen exposure to develop specific responses. - The phrase "no antigen exposure" describes how the **innate immune system** functions, providing immediate, non-specific protection without prior contact with a pathogen. *Immediate response* - **Innate immunity** provides an immediate, non-specific response to pathogens. - **Acquired immunity** takes time to develop (days to weeks) after initial antigen exposure, but provides a faster response upon re-exposure due to immunological memory.
Question 3: Cell surface molecules involved in peripheral tolerance induction are
- A. CD40 and CD40L
- B. CD34 and CD51
- C. B7 and CD28 (Correct Answer)
- D. B7 and CD3
Explanation: ***B7 and CD28*** - B7 is crucial for providing a **costimulatory signal** to T cells via interaction with CD28, promoting **T cell activation** and peripheral tolerance [1][2]. - This interaction is essential in preventing autoimmune responses by ensuring T cells require both antigen and costimulatory signals for full activation [1][3]. *B7 and CD3* - CD3 is a part of the T cell receptor (TCR) complex, primarily involved in **T cell activation**, not specifically in peripheral tolerance. - The interaction of B7 with **CD3** does not provide the costimulatory signal necessary for peripheral tolerance [3]. *CD34 and CD51* - CD34 is primarily involved in **hematopoietic stem cell trafficking** and does not play a role in T cell tolerance mechanisms. - CD51 is associated with **integrins** and plays a role in adhesion rather than in peripheral tolerance induction. *CD40 and CD40L* - While CD40-CD40L interactions are important for **B cell activation** and other immune responses, they are not directly involved in the inductive mechanisms of **peripheral tolerance** in T cells. - They primarily mediate costimulatory signals in **adaptive immunity**, not specifically for tolerance purposes. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 204-206. [2] 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. 157-158. [3] 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. 176-177.
Question 4: All are true regarding the development of T-cells, except?
- A. T-cells are formed in bone marrow
- B. In lymph nodes, T-cells are found in paracortical area
- C. Maturation of T-cells take place in thymus
- D. T-cells are located in mantle layer of spleen (Correct Answer)
Explanation: ***T-cells are located in mantle layer of spleen*** - The **mantle layer** (or marginal zone) of the spleen is primarily associated with **B-lymphocytes**, which are involved in antibody production. - While T-cells are present in the spleen, they are predominantly found in the **periarteriolar lymphoid sheath (PALS)**, which is part of the white pulp, rather than the mantle layer. *T-cells are formed in bone marrow* - **Hematopoietic stem cells** in the **bone marrow** are the progenitors of all blood cells, including lymphocytes. - These stem cells differentiate into **lymphoid stem cells**, which then travel to the thymus to become T-cells. *Maturation of T-cells take place in thymus* - **T-cell precursors** migrate from the bone marrow to the **thymus**, where they undergo a complex process of differentiation and selection. - In the thymus, T-cells acquire their **T-cell receptors (TCRs)** and undergo positive and negative selection to ensure they are self-MHC restricted and tolerant to self-antigens. *In lymph nodes, T-cells are found in paracortical area* - The **paracortical area** (or paracortex) of the lymph node is the **T-cell zone**, rich in T-lymphocytes and dendritic cells. - This region is crucial for the interaction between T-cells and antigen-presenting cells, initiating adaptive immune responses.
Question 5: Which of the following statements regarding rejection of solid organ transplants is true?
- A. Most immunosuppressive medications are used to prevent chronic rejection
- B. The major cause of graft failure is acute rejection
- C. Liver transplants are especially susceptible to hyperacute rejection
- D. Hyperacute rejection begins in the operating room with reperfusion of the transplanted organ (Correct Answer)
Explanation: ***Hyperacute rejection begins in the operating room with reperfusion of the transplanted organ*** - **Hyperacute rejection** is a rapidly-occurring immune response that starts almost immediately after the transplanted organ is re-vascularized, often while the patient is still in the operating room [1]. - This type of rejection is mediated by **pre-formed antibodies** (e.g., ABO blood group antibodies or anti-HLA antibodies) in the recipient's circulation that bind to antigens on the donor organ's endothelium, leading to massive thrombosis and organ destruction [1]. *Most immunosuppressive medications are used to prevent chronic rejection* - While immunosuppressants play a role in mitigating **chronic rejection**, their primary and most effective targets are **acute rejection episodes** and the initial prevention of organ rejection [2]. - **Chronic rejection** is often a more complex process involving both immune and non-immune factors, and current immunosuppressive regimens are less effective at completely preventing or reversing it compared to acute rejection. *The major cause of graft failure is acute rejection* - In the long term, **chronic rejection** (or chronic allograft dysfunction) is the leading cause of late graft loss, rather than acute rejection. - With advancements in immunosuppression, **acute rejection rates** have significantly decreased, making chronic issues and non-immune factors more prominent in overall graft failure. *Liver transplants are especially susceptible to hyperacute rejection* - **Liver transplants** are notably more tolerant to ABO and HLA mismatches compared to other solid organ transplants (like kidney or heart). - This relative immunotolerance means that **hyperacute rejection** is far less common in liver transplantation. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 241-242. [2] 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. 180-181.
Question 6: What is the inheritance pattern of the ABO blood group system and the HLA system?
- A. Pseudodominance
- B. Autosomal dominant
- C. Autosomal recessive
- D. Codominant (Correct Answer)
Explanation: ### Explanation **Correct Option: D (Codominant)** The ABO blood group and the Human Leukocyte Antigen (HLA) system are classic examples of **codominance**. In codominance, both alleles in a heterozygous individual are fully expressed, and neither masks the other. * **ABO System:** The $I^A$ and $I^B$ alleles are codominant. If an individual inherits $I^A$ from one parent and $I^B$ from the other, their phenotype is AB, expressing both A and B antigens on the RBC surface. (Note: Both $I^A$ and $I^B$ are dominant over the $i$ allele). * **HLA System:** HLA genes (located on Chromosome 6) are the most polymorphic genes in humans. An individual expresses HLA antigens from both maternal and paternal haplotypes simultaneously on the cell surface. This is critical for immune recognition and organ transplant matching. **Why other options are incorrect:** * **A. Pseudodominance:** This occurs when a recessive allele is expressed because the dominant allele is missing (e.g., due to deletion), commonly seen in X-linked disorders in males. * **B & C. Autosomal Dominant/Recessive:** These follow Mendelian patterns where one allele masks the other. In ABO, while A and B are dominant over O, they do not mask each other, making "Codominant" the more specific and accurate description. **High-Yield Facts for NEET-PG:** 1. **Multiple Allelism:** The ABO system is also an example of multiple allelism (three alleles: A, B, and O). 2. **Bombay Phenotype:** A rare condition where the H-substance is missing; these individuals phenotypically appear as Type O regardless of their genotype. 3. **HLA Association:** HLA-B27 is strongly associated with Ankylosing Spondylitis; HLA-DR3/DR4 is associated with Type 1 Diabetes Mellitus. 4. **Chromosome 9:** The locus for the ABO gene is on the long arm of Chromosome 9.
Question 7: All of the following are functions of the spleen EXCEPT?
- A. Clearance of damaged or aged red blood cells (RBCs) from the blood.
- B. Extramedullary site for hematopoiesis and recycling iron.
- C. Initiation of adaptive immune response from filtration of lymph. (Correct Answer)
- D. Clearance of encapsulated bacteria from the bloodstream.
Explanation: ### Explanation The correct answer is **C. Initiation of adaptive immune response from filtration of lymph.** The spleen is often described as a "giant lymph node," but there is a critical anatomical difference: **the spleen filters blood, not lymph.** Lymph nodes are responsible for filtering interstitial fluid (lymph) via afferent lymphatic vessels. The spleen lacks afferent lymphatics; instead, it samples antigens directly from the systemic circulation via the splenic artery. #### Analysis of Options: * **Option A (Correct Function):** The splenic sinusoids and the "pitting" mechanism in the Red Pulp act as a biological filter, removing senescent, rigid, or damaged RBCs (Culling). * **Option B (Correct Function):** During fetal development (months 3–7), the spleen is a primary hematopoietic organ. In adults, it can resume this role (extramedullary hematopoiesis) in conditions like myelofibrosis. It also recycles iron from hemoglobin via splenic macrophages. * **Option D (Correct Function):** The White Pulp contains B-cells and T-cells. Splenic macrophages and antibodies are essential for opsonizing and clearing **encapsulated organisms** (e.g., *S. pneumoniae, H. influenzae, N. meningitidis*). #### High-Yield Clinical Pearls for NEET-PG: * **Asplenia/Splenectomy:** Patients are at high risk for **OPSI (Overwhelming Post-Splenectomy Infection)**. Vaccination against encapsulated bacteria is mandatory (ideally 2 weeks before elective surgery). * **Howell-Jolly Bodies:** These are nuclear remnants in RBCs normally removed by the spleen; their presence on a peripheral smear is a hallmark of splenic dysfunction or asplenia. * **Pitting:** The spleen’s ability to remove inclusions (like malaria parasites or Heinz bodies) from RBCs without destroying the cell itself.
Question 8: What is the first cell in the development of red blood cells?
- A. Proerythroblast (Correct Answer)
- B. Intermediate normoblast
- C. Reticulocyte
- D. Basophilic erythroblast
Explanation: **Explanation:** The process of red blood cell formation, known as **erythropoiesis**, occurs in the bone marrow. It begins with a multipotent hematopoietic stem cell, which differentiates into a **Proerythroblast** (also called a Pronormoblast). **Why Proerythroblast is correct:** The Proerythroblast is the **first morphologically identifiable committed precursor** of the erythroid series. It is a large cell with a big nucleus, visible nucleoli, and a thin rim of basophilic cytoplasm. Once a stem cell differentiates into a proerythroblast, it is "committed" to becoming a mature erythrocyte. **Analysis of Incorrect Options:** * **Basophilic erythroblast (Early Normoblast):** This is the second stage. It is smaller than the proerythroblast and shows intense cytoplasmic basophilia due to an accumulation of RNA for hemoglobin synthesis. * **Intermediate normoblast (Polychromatophilic erythroblast):** This is the third stage. It is characterized by a "checkered" nucleus and a cytoplasm that appears grayish/purple because it contains both basic RNA and acidic hemoglobin. * **Reticulocyte:** This is the penultimate stage, occurring after the nucleus is extruded (at the orthochromatic stage). It is an immature RBC that stays in the marrow for 1–2 days before entering the peripheral circulation. **NEET-PG High-Yield Pearls:** 1. **Hemoglobin synthesis** begins in the **Proerythroblast** stage, but becomes visible (morphologically detectable) in the **Intermediate Normoblast** stage. 2. The **nucleus is extruded** at the **Orthochromatic Normoblast** (Late Normoblast) stage. 3. **Reticulocyte count** is the best clinical indicator of effective erythropoiesis in the bone marrow. 4. **Erythropoietin (EPO)** primarily acts on the CFU-E (Colony Forming Unit-Erythroid) to stimulate the production of proerythroblasts.
Question 9: The biconcave shape of RBC is useful for all the following functions EXCEPT:
- A. Allows considerable alteration in cell volume
- B. Increasing surface area for diffusion (Correct Answer)
- C. Resisting hemolysis
- D. Passing easily through smaller capillaries
Explanation: The biconcave shape of the Red Blood Cell (RBC) is a specialized structural adaptation designed for flexibility and volume management rather than maximizing surface area. ### **Explanation of the Correct Answer** **Option B (Increasing surface area for diffusion)** is the correct answer because it is a common misconception. Mathematically, a **sphere** has the minimum surface area for a given volume, while a **flat disc** or complex shape has more. However, the biconcave shape is *not* the most efficient shape for maximizing surface area; a thin, flat sheet or a highly folded membrane would provide more area for gas exchange. The primary evolutionary "goal" of the biconcave shape is to provide a high **surface-area-to-volume ratio**, which allows for significant cell deformation and volume changes without stretching the membrane. ### **Analysis of Other Options** * **Option A & C:** The biconcave shape provides "excess" membrane. This allows the RBC to undergo **considerable alteration in cell volume** (swelling in hypotonic solutions) without rupturing. Because the membrane isn't under tension in its resting state, it can expand into a spherical shape before bursting, thereby **resisting hemolysis**. * **Option D:** RBCs (7.5 µm) must pass through splenic sinusoids and capillaries as small as 3 µm. The biconcave shape allows the cell to fold and deform easily (**high deformability**), facilitating passage through narrow microvasculature. ### **High-Yield Clinical Pearls for NEET-PG** * **Hereditary Spherocytosis:** A defect in membrane proteins (Ankyrin/Spectrin) causes RBCs to lose their biconcave shape and become spherical. These cells have the *lowest* surface-area-to-volume ratio, are fragile, and are easily destroyed in the spleen. * **Average RBC Diameter:** 7.5 µm (Thickness: 2 µm at periphery, 1 µm at center). * **Rouleaux Formation:** The biconcave shape facilitates the "stacking" of RBCs, seen in states of high ESR (e.g., chronic inflammation).
Question 10: Which of the following is responsible for the adhesion of platelets to the vessel wall?
- A. Von Willebrand factor (Correct Answer)
- B. Factor IX
- C. Fibrinogen
- D. Fibronectin
Explanation: **Explanation:** The correct answer is **Von Willebrand factor (vWF)**. Platelet plug formation occurs in three distinct stages: Adhesion, Activation, and Aggregation. 1. **Why vWF is correct:** When a blood vessel is injured, the subendothelial collagen is exposed. Platelets cannot bind directly to collagen under high-shear stress (like in arteries). **vWF** acts as a molecular bridge; one end binds to the exposed **subendothelial collagen**, and the other end binds to the **Glycoprotein Ib (GpIb)** receptor on the platelet surface. This specific interaction is responsible for **platelet adhesion**. 2. **Why the other options are incorrect:** * **Factor IX:** This is a component of the intrinsic pathway of the coagulation cascade. Its deficiency leads to Hemophilia B (Christmas disease). It is involved in secondary hemostasis (clotting), not primary platelet adhesion. * **Fibrinogen:** This is responsible for **platelet aggregation**. Fibrinogen binds to the **GpIIb/IIIa** receptors on adjacent platelets, linking them together to form a plug. * **Fibronectin:** While fibronectin is present in the extracellular matrix and plasma and plays a minor role in cell-matrix interactions, it is not the primary mediator of initial platelet adhesion to the vessel wall. **High-Yield Clinical Pearls for NEET-PG:** * **Bernard-Soulier Syndrome:** A deficiency of the **GpIb** receptor, leading to defective adhesion (characterized by giant platelets and thrombocytopenia). * **Von Willebrand Disease (vWD):** The most common inherited bleeding disorder; it results in defective adhesion due to a deficiency or dysfunction of vWF. * **Glanzmann Thrombasthenia:** A deficiency of the **GpIIb/IIIa** receptor, leading to defective **aggregation**. * **vWF Source:** It is synthesized in endothelial cells (stored in **Weibel-Palade bodies**) and megakaryocytes (stored in **α-granules** of platelets).
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