Cells and Organs of Immune System — MCQs
Antigen presented on MHC class I molecules activates which of the following cells?
IL-2 is secreted by?
All of the following are features of Lymph node histology except:
CD 40 marker is absent in the person. Which of the following would be seen?
Cell surface molecules involved in peripheral tolerance induction are
Which of the following is considered the most professional antigen presenting cell (APC) in the immune system?
All are true regarding the development of T-cells, except?
Which of the following components are involved in non-IgE mediated anaphylactic reactions?
Which interleukin is specifically secreted by Th17 cells?
MHC II is associated with:-
Cells and Organs of Immune System Indian Medical PG Practice Questions and MCQs
Question 1: Antigen presented on MHC class I molecules activates which of the following cells?
- A. NK cells
- B. Helper cells
- C. B cells
- D. Cytotoxic T cells (Correct Answer)
Explanation: ***Cytotoxic T cells*** - **MHC class I** molecules present **intracellular antigens** (e.g., viral or tumor antigens) to **CD8+ T cells** (cytotoxic T cells). - This binding activates the cytotoxic T cells, leading to the destruction of the **infected** or **abnormal host cell**. *NK cells* - **Natural Killer (NK) cells** recognize and kill target cells that have **reduced or absent MHC class I** expression, which often occurs in virally infected or tumor cells, not cells presenting antigens on MHC class I. - They are part of the **innate immune system** and do not require prior sensitization or MHC-peptide presentation for activation. *Helper cells* - **Helper T cells** (CD4+ T cells) recognize antigens presented on **MHC class II** molecules, typically expressed by **antigen-presenting cells** (APCs) like macrophages, B cells, and dendritic cells. - Their primary role is to **orchestrate immune responses** by releasing cytokines. *B cells* - **B cells** are primarily involved in **humoral immunity**, producing antibodies after recognizing specific antigens directly via their B cell receptors or with T cell help. - While they can present antigens on **MHC class II** to helper T cells, direct antigen binding to **MHC class I** does not activate B cells.
Question 2: IL-2 is secreted by?
- A. Helper T-cells (Correct Answer)
- B. Neutrophils
- C. NK cells
- D. Macrophages
Explanation: ***Helper T-cells*** - **Helper T-cells** (CD4+ T-cells) are the **primary source of IL-2** upon activation by antigen presentation. - **IL-2** acts as a **T-cell growth factor**, essential for the clonal expansion of antigen-specific T-cells and immune response amplification. - Activated **CD8+ cytotoxic T-cells** also produce IL-2, though in smaller amounts. *Neutrophils* - **Neutrophils** are phagocytic cells primarily involved in acute inflammation and bacterial killing. - They mainly produce **chemokines** and **pro-inflammatory cytokines** like IL-8 and IL-1β, but do not secrete significant amounts of IL-2. *NK cells* - **Natural Killer (NK) cells** are part of the innate immune system and are crucial for targeting virus-infected and tumor cells. - While activated NK cells can produce small amounts of IL-2, they are primarily **IL-2 responders** rather than major producers. - NK cells predominantly secrete **IFN-gamma** and **TNF-alpha** upon activation. *Macrophages* - **Macrophages** are antigen-presenting cells that phagocytose pathogens and cellular debris. - They predominantly secrete **pro-inflammatory cytokines** such as TNF-alpha, IL-1, IL-6, and IL-12, rather than IL-2.
Question 3: All of the following are features of Lymph node histology except:
- A. Both Efferent and Afferent are present
- B. Subcapsular sinus present
- C. Cortex and Medulla are present
- D. Red pulp and White pulp are present (Correct Answer)
Explanation: ***Red pulp and White pulp are present*** - **Red pulp** and **white pulp** are characteristic histological features of the **spleen**, not lymph nodes [1]. - The white pulp contains lymphoid follicles (PALS - periarteriolar lymphoid sheaths), while the red pulp is involved in filtering blood and destroying old red blood cells [1]. - This is the feature that does NOT belong to lymph node histology. *Both Efferent and Afferent are present* - Lymph nodes have multiple **afferent lymphatic vessels** that bring lymph into the node and usually one or two **efferent lymphatic vessels** that carry lymph away [2]. - This arrangement allows for efficient filtering of lymph and immune surveillance [2]. - This IS a feature of lymph nodes. *Subcapsular sinus present* - The **subcapsular sinus** is a space located directly beneath the capsule of the lymph node, which receives lymph from the afferent lymphatic vessels. - It contains a network of reticular fibers and macrophages, acting as the initial filtering area. - This IS a feature of lymph nodes. *Cortex and Medulla are present* - Lymph nodes are histologically divided into an outer **cortex** and an inner **medulla**. - The cortex contains lymphoid follicles (B-cell areas) and paracortical areas (T-cell areas), while the medulla consists of medullary cords and sinuses. - This IS a feature of lymph nodes.
Question 4: CD 40 marker is absent in the person. Which of the following would be seen?
- A. Impaired Macrophage function
- B. Impaired NK cell function
- C. Impaired B cell function (Correct Answer)
- D. Impaired T cell function
Explanation: ***Impaired B cell function*** - The **CD40 receptor** on B cells is crucial for receiving co-stimulatory signals from **CD40 ligand (CD40L)**, primarily expressed on activated T cells. - Absence of CD40 on B cells prevents proper **T-cell dependent antibody class switching** and germinal center formation, leading to impaired B cell activation, immunoglobulin production, and immune responses. - This condition is seen in **Hyper-IgM Syndrome Type 3** (very rare autosomal recessive disorder). *Impaired Macrophage function* - While macrophages express CD40, its absence would primarily affect their ability to be fully activated by T cells and present antigens, but the most direct and profound impact of absent CD40 is on B cells themselves. - Macrophages have other activation pathways not directly dependent on CD40. *Impaired NK cell function* - **Natural killer (NK) cells** primarily recognize and kill target cells lacking MHC class I molecules or those expressing activating ligands, independent of CD40 signaling. - NK cell function is not directly regulated by the CD40-CD40L interaction. *Impaired T cell function* - While **T cells express CD40L** (the ligand for CD40), the question specifies the absence of the **CD40 marker** itself, which is expressed on B cells, not T cells. - T cell function involves antigen recognition, activation, and cytokine production, which are not directly mediated by CD40 expression on T cells. - T-cell function would be indirectly affected due to the lack of proper B cell help and antigen presentation, but the direct impact of absent CD40 is on the cell expressing it (B cells).
Question 5: 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 6: Which of the following is considered the most professional antigen presenting cell (APC) in the immune system?
- A. B cells
- B. Dendritic cells (Correct Answer)
- C. T cells
- D. NK cells
Explanation: ***Dendritic cells*** - **Dendritic cells** are specialized for capture, processing, and presentation of antigens to T lymphocytes. - They are often referred to as the "**professional APCs**" due to their superior ability to initiate primary T cell responses. *B cells* - While B cells can present antigens, they are generally less efficient than **dendritic cells** and primarily serve to present antigens to **helper T cells** during secondary immune responses. - Their main role is **antibody production** after activation, not initiating primary T cell responses. *T cells* - **T cells** are effector cells of the adaptive immune system and recognize antigen presented by APCs; they do not typically function as antigen-presenting cells themselves. - Some T cells, like **gamma-delta T cells**, can present antigens, but this is not their primary role. *NK cells* - **Natural Killer (NK) cells** are part of the innate immune system and primarily target and kill infected or cancerous cells without prior sensitization. - They do not present antigens in the classical sense and are not considered professional APCs.
Question 7: 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 8: Which of the following components are involved in non-IgE mediated anaphylactic reactions?
- A. Complement
- B. Ig G
- C. Ig M
- D. All of the options (Correct Answer)
Explanation: ***All of the options*** - **Non-IgE mediated anaphylactic reactions** can involve various immune components beyond IgE, including **IgG**, **IgM**, and the **complement system**. - For instance, **IgG antibodies** can bind to mast cells or basophils and trigger degranulation, while **complement activation** can directly release anaphylatoxins, both leading to anaphylactoid symptoms. *Ig G* - While many anaphylactic reactions are **IgE-mediated**, **IgG antibodies** can also contribute to anaphylaxis, particularly in drug reactions or reactions to biologics. - **IgG-mediated anaphylaxis** often involves immune complexes that activate mast cells or basophils through Fcγ receptors. *Ig M* - **IgM antibodies** are less commonly implicated in direct anaphylactic reactions compared to IgE or IgG. - However, **IgM** can play a role in complex formation that activates the complement system, indirectly contributing to **anaphylactoid responses**. *Complement* - The **complement system** can be directly activated by certain drugs, physical stimuli, or immune complexes without the involvement of immunoglobulins. - This activation releases **anaphylatoxins (C3a, C4a, C5a)**, which can directly degranulate mast cells and basophils, leading to symptoms mimicking true anaphylaxis.
Question 9: Which interleukin is specifically secreted by Th17 cells?
- A. IFN Gamma
- B. IL6
- C. IL-17 (Correct Answer)
- D. IL-22
Explanation: ***IL22*** - Th17 cells predominantly secrete **IL-17** and also produce **IL-22**, which is significant in mucosal immunity and inflammation [1]. - **IL-22** plays a crucial role in the response to infections and in the pathogenesis of inflammatory diseases. *IL16* - IL-16 is primarily associated with **chemoattractant and regulatory functions** for lymphocytes and not directly secreted by Th17 cells. - It is involved in **eosinophil and T cell activation**, which is not characteristic of the Th17 response. *IFN Gamma* - IFN-gamma is mainly produced by **Th1 cells** and is critical for **cell-mediated immunity**, which is distinct from the function of Th17 cells. - It plays a role in activating **macrophages**, unlike Th17 cells which focus on **neutrophil recruitment** and inflammation. *IL6* - While IL-6 is a pro-inflammatory cytokine that can be involved in various immune responses, it is not primarily secreted by Th17 cells. - It is produced by a variety of cell types including fibroblasts and macrophages, acting as a mediator in the **acute phase response**. **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. 158-160.
Question 10: MHC II is associated with:-
- A. Red blood cells
- B. Antigen presenting cells (Correct Answer)
- C. Platelets
- D. Epithelial cells
Explanation: ***Antigen presenting cells*** - **MHC II (Major Histocompatibility Complex class II)** molecules are primarily expressed on the surface of professional **antigen-presenting cells (APCs)**. - APCs, such as **macrophages**, **dendritic cells**, and **B lymphocytes**, use MHC II to present **extracellularly derived antigens** to **CD4+ T helper cells**. *Red blood cells* - **Red blood cells (RBCs)** are anucleated and lack MHC molecules entirely. - Their primary function is **oxygen transport**, not immune cell communication. *Platelets* - **Platelets** are cell fragments involved in **hemostasis** (blood clotting). - They do not express MHC class II molecules as they are not involved in antigen presentation. *Epithelial cells* - Most **epithelial cells** primarily express **MHC class I** molecules to present **intracellular antigens** to **CD8+ cytotoxic T cells**. - They do not typically express MHC class II unless under specific inflammatory conditions, and even then, not as their primary function.
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