Immunology Practice Questions

Q: T-cells mature in:

Thymus. **Explanation:** The development of T-lymphocytes is a multi-stage process involving primary and secondary lymphoid organs. **1. Why Thymus is Correct:** T-cells originate from hematopoietic stem cells in the **bone marrow** but migrate to the **Thymus** for maturation and differentiation (hence the name "T" cells). In the thymus, thymocytes undergo **positive selection** (ensuring they recognize MHC molecules) and **negative selection** (eliminating self-reactive cells). This process ensures central tolerance and produces mature, immunocompetent T-cells (CD4+ and CD8+) that then enter the peripheral circulation. **2. Analysis of Incorrect Options:** * **Peyer’s Patches & Lymph Nodes:** These are **secondary lymphoid organs**. They are sites where mature lymphocytes encounter antigens and undergo activation and clonal expansion, but they are not sites of initial maturation. * **Bursa of Fabricius:** This is a primary lymphoid organ found only in **birds**, where B-cell maturation occurs. In humans, the functional equivalent for B-cell maturation is the **Bone Marrow**. **Clinical Pearls for NEET-PG:** * **DiGeorge Syndrome:** Characterized by thymic hypoplasia (3rd/4th pharyngeal pouch defect), leading to profound T-cell deficiency and recurrent viral/fungal infections. * **Hassall’s Corpuscles:** These are characteristic epithelial whorls found in the **thymic medulla**, a key histological marker. * **Involution:** The thymus is most active during childhood and undergoes fatty involution after puberty, though it continues to produce T-cells at a lower rate throughout life.

Q: Which of the following cells is known as large granular lymphocyte (LGL)?

NK cells. **Explanation:** **Natural Killer (NK) cells** are the correct answer. Morphologically, they are identified as **Large Granular Lymphocytes (LGLs)**. Unlike typical small lymphocytes, NK cells possess a more abundant cytoplasm containing distinct azurophilic granules. These granules house cytotoxic proteins like **perforins** and **granzymes**, which the cells use to induce apoptosis in virus-infected or tumor cells without prior sensitization (Innate Immunity). **Analysis of Incorrect Options:** * **Plasma cells:** These are differentiated B-cells characterized by an eccentric nucleus, a prominent perinuclear halo (Golgi apparatus), and a "cartwheel" or "clock-face" chromatin pattern. They are not granular lymphocytes. * **T cells:** Most circulating T-cells are small, agranular lymphocytes. While some activated cytotoxic T-cells (CD8+) can exhibit an LGL morphology, the term "Large Granular Lymphocyte" is classically and primarily synonymous with NK cells in medical literature. * **K cells:** These are cells that mediate Antibody-Dependent Cellular Cytotoxicity (ADCC). While most K-cell activity is actually performed by NK cells, the term "K cell" refers to a functional classification rather than a distinct morphological cell type like LGL. **High-Yield Facts for NEET-PG:** * **Markers:** NK cells are identified by **CD56** and **CD16** (FcγRIII), and they lack CD3 (T-cell marker). * **MHC Restriction:** NK cells are **not** MHC-restricted (unlike T-cells). They are inhibited by the presence of MHC-I on healthy cells. * **Cytokine Production:** They are a major source of **IFN-gamma**, which activates macrophages. * **Clinical Correlation:** Chediak-Higashi syndrome involves a defect in granule formation, leading to impaired NK cell function and recurrent infections.

Q: Which complement component is involved in both the classical and alternate pathways?

C3. ### Explanation The complement system consists of a cascade of proteins that play a vital role in innate immunity. The correct answer is **C3** because it serves as the central convergence point for all complement activation pathways. **Why C3 is the Correct Answer:** * **Central Role:** C3 is the most abundant complement protein in the plasma. * **Classical Pathway:** Activation leads to the formation of the C3 convertase (**C4b2a**), which cleaves C3 into C3a and C3b. * **Alternative Pathway:** This pathway involves the spontaneous hydrolysis of C3 ("tick-over") and the formation of the alternative C3 convertase (**C3bBb**). * **Convergence:** Regardless of the initiation method (antigen-antibody complexes, lectins, or microbial surfaces), all pathways must activate C3 to proceed toward the formation of the Membrane Attack Complex (MAC). **Analysis of Incorrect Options:** * **A. C1:** Involved exclusively in the **Classical pathway**. It binds to the Fc portion of IgM or IgG. * **B. C2:** A component of the **Classical and Lectin pathways**. It is not involved in the Alternative pathway (which uses Factor B instead). * **D. C5:** While C5 is involved in the "Late Phase" or "Terminal Pathway" common to all pathways, it is activated *downstream* of C3. C3 is the first component where the initial distinct cascades truly merge. **NEET-PG High-Yield Pearls:** * **C3 deficiency:** Associated with recurrent pyogenic infections (e.g., *S. pneumoniae*, *H. influenzae*) and Type III hypersensitivity reactions (Glomerulonephritis). * **C3b function:** Acts as a potent **opsonin** (facilitates phagocytosis). * **C3a, C4a, C5a:** Known as **anaphylatoxins**; they trigger mast cell degranulation. C5a is also a potent chemoattractant for neutrophils. * **Alternative Pathway:** The only pathway that does not require specific antibodies for initiation, making it a key part of the immediate innate immune response.

Q: MHC class 1 proteins are not present on which of the following?

RBC. **Explanation:** The correct answer is **RBC (Red Blood Cells)**. **1. Why RBC is correct:** MHC Class I molecules are expressed on the surface of almost all **nucleated cells** in the body. Their primary function is to present endogenous antigens to CD8+ Cytotoxic T-cells. Since mature human erythrocytes (RBCs) lack a nucleus and the necessary protein-synthesizing machinery (ribosomes/endoplasmic reticulum), they do not express MHC Class I proteins. This is clinically significant as it prevents T-cell mediated destruction of RBCs and is one reason why blood transfusions focus on ABO/Rh compatibility rather than HLA matching. **2. Why other options are incorrect:** * **Platelets:** Although they lack a nucleus, platelets are derived from megakaryocytes and **do express** MHC Class I molecules on their surface. This is a high-yield distinction often tested in exams. * **T-cells:** As nucleated white blood cells, T-cells express MHC Class I. (Note: They only express MHC Class II when activated). * **Macrophages:** These are nucleated cells and professional Antigen Presenting Cells (APCs). They express **both** MHC Class I (to show they are "self") and MHC Class II (to present exogenous antigens to CD4+ T-cells). **High-Yield Clinical Pearls for NEET-PG:** * **MHC Class I:** Present on all nucleated cells + Platelets. (Mnemonic: **1** x CD**8** = 8). * **MHC Class II:** Present only on Professional APCs (B-cells, Macrophages, Dendritic cells) and thymic epithelial cells. (Mnemonic: **2** x CD**4** = 8). * **Exceptions:** Neurons, corneal endothelium, and villous trophoblasts also show very low or absent MHC I expression, making them "immunologically privileged" sites.

Q: The use of hyperimmune sera such as hepatitis B immune globulin, rabies immunoglobulin, and human tetanus immune globulin for prophylaxis or treatment is an example of what process?

Passive immunity. ### Explanation **Correct Option: B. Passive immunity** **Why it is correct:** Passive immunity involves the transfer of **pre-formed antibodies** (immunoglobulins) from an external source (human or animal) to a recipient. In the cases of Hepatitis B immune globulin (HBIG), Rabies immunoglobulin (RIG), and Tetanus immune globulin (TIG), the body does not produce its own immune response; instead, it receives immediate, "ready-made" protection. This is essential for post-exposure prophylaxis where there is no time for the host's immune system to mount a primary response. **Why other options are incorrect:** * **A. Active immunity:** This occurs when the host’s own immune system is stimulated to produce antibodies and memory cells, usually via natural infection or **vaccination** (e.g., Hep B vaccine). It has a lag period but provides long-lasting protection. * **C. Humoral immunity:** While immunoglobulins are part of the humoral (antibody-mediated) system, this term describes the *arm* of the immune system rather than the *process* of acquiring immunity. Both active and passive immunity can be humoral. * **D. Cellular immunity:** This refers to T-cell mediated immunity (CD4+ and CD8+ cells) which does not involve antibodies and is not the mechanism provided by hyperimmune sera. **High-Yield Clinical Pearls for NEET-PG:** * **Onset vs. Duration:** Passive immunity provides **immediate** protection but is **short-lived** (weeks to months) because no memory cells are formed. * **Natural vs. Artificial Passive Immunity:** * *Natural:* IgG crossing the placenta or IgA in colostrum. * *Artificial:* Administration of HBIG, RIG, TIG, or Antisnake venom (ASV). * **Combined Prophylaxis:** For Rabies and Tetanus (in non-immunized individuals), both active (vaccine) and passive (IG) immunity are often given simultaneously at different sites to provide both immediate and long-term protection.

Question 1

Immune tolerance can be induced by?

Accepted Answer

Excess antigen

Answer

Excess antibody

Answer

Excess complement level

Answer

Neonatal thymectomy

Question 2

T-cells mature in:

Accepted Answer

Thymus

Answer

Peyer's patches

Answer

Lymph node

Answer

Bursa of Fabricius

Question 3

T4/T8 ratio reversal is seen in which of the following conditions?

Accepted Answer

AIDS

Answer

T-cell lymphoma

Answer

Hairy cell leukemia

Answer

Infectious mononucleosis

Question 4

Which complement component(s) are necessary for Neisseria infection?

Accepted Answer

All of the above

Answer

C5

Answer

C6

Answer

C7

Question 5

Which of the following cells is known as large granular lymphocyte (LGL)?

Accepted Answer

NK cells

Answer

Plasma cells

Answer

T cells

Answer

K cells

Question 6

A child, after ingesting shellfish, developed a tingling sensation in the mouth, swelling of the face, lips, and tongue, and also complained of abdominal pain and dizziness. This is an example of which type of hypersensitivity reaction?

Accepted Answer

IgE mediated reaction

Answer

IgG mediated reaction

Answer

IgA mediated reaction

Answer

T cell mediated cytotoxicity

Question 7

Which complement component is involved in both the classical and alternate pathways?

Accepted Answer

C3

Answer

C1

Answer

C2

Answer

C5

Question 8

MHC class 1 proteins are not present on which of the following?

Accepted Answer

RBC

Answer

Platelets

Answer

T-cells

Answer

Macrophage

Question 9

The use of hyperimmune sera such as hepatitis B immune globulin, rabies immunoglobulin, and human tetanus immune globulin for prophylaxis or treatment is an example of what process?

Accepted Answer

Passive immunity

Answer

Active immunity

Answer

Humoral immunity

Answer

Cellular immunity

Question 10

A 40-year-old male patient complains of difficulty in breathing and has a history of multiple allergies to food and dust. Which immunoglobulin is characteristically elevated in this patient?

Accepted Answer

Immunoglobulin E (IgE)

Answer

Immunoglobulin A (IgA)

Answer

Immunoglobulin M (IgM)

Answer

Immunoglobulin G (IgG)

Immunology — MCQs

Immunology — MCQs

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