Cellular I mmunology

# Cellular Immunology ## Microbiology Examination **Student Information:** * **Name:** ................................. * **Registration Number:** BMS/2023/.................. * **Programme:** Bachelor of Medicine and Bachelor of Surgery (MBChB) * **Year:** 2 **Examination Details:** * **End of Term CAT** * **Semester:** January – April, 2024/2025 * **Date:** 26th March 2025 * **Unit Code:** MBMM 2511 * **Unit Title:** Cellular Immunology * **Time Allotted:** 2 Hours ### Instructions: * Answer **all questions** in **Sections A & B**. ## SECTION A: Multiple Choice Questions (MCQs) ### Question 1 The ability of an organism to resist **infections** by the **pathogens** is called: a) Infection b) Hypersensitivity c) Immunity d) Allergy e) Attenuation **Answer: c) Immunity** **Explanation:** **Immunity** is the body's natural **defense mechanism** against **pathogenic microorganisms**, **toxins**, and other harmful substances. ### Question 2 Name the group of **pattern recognition molecules** which functions exclusively as a **signaling receptor**: a) CRP b) Toll-like receptor c) MBL d) LPS e) MMLS **Answer: b) Toll-like receptor** **Explanation:** **Toll-like receptors (TLRs)** are **pattern recognition receptors** that recognize **PAMPs** and function exclusively as **signaling receptors**. ### Question 3 Name the first **cells** which are recruited at the place of **infection**: a) NK cells b) Basophils c) Neutrophils d) Macrophages e) A and B **Answer: c) Neutrophils** **Explanation:** **Neutrophils** are the first **immune cells** to arrive at the **site of infection** during **acute inflammation**. ### Question 4 Which of the following **antibody** gives a **primary immune reaction**: a) IgG b) IgM c) IgA d) IgE e) A and B **Answer: b) IgM** **Explanation:** **IgM** is the first **antibody** produced during a **primary immune response** and is most effective at **complement activation**. ### Question 5 Which of these is NOT a characteristic feature of **adaptive immunity**: a) Immunogenic memory b) Antigen non-specific c) Self/non-self recognition d) Diversity e) None of the above **Answer: b) Antigen non-specific** **Explanation:** **Adaptive immunity** is highly **antigen-specific**, unlike **innate immunity** which is **non-specific**. ### Question 6 The major role of the **complement system** is to work in conjunction with: a) **Antibodies** to **lyse cells** via the **C8** and **C9 components** b) Antibodies to lyse cells via the perforin molecules c) Antibodies to opsonize cells d) The major histocompatibility complex for cell recognition e) The T-cell receptor for production of lymphokines **Answer: a) Antibodies to lyse cells via the C8 and C9 components** **Explanation:** The **complement system** works with **antibodies** to form the **membrane attack complex (MAC)** using **C5b-C9 components**. ### Question 7 One principal function of **complement** is to: a) Bind **antibodies** attached to **cell surfaces** and to **lyse these cells** b) Cross-link allergens c) Inactivate perforins d) Mediate the release of histamine e) Phagocytize antigens **Answer: a) Bind antibodies attached to cell surfaces and to lyse these cells** **Explanation:** The **complement system** binds to **antibodies** on target cells and forms **MAC** to **lyse the cells**. ### Question 8 **Complement component C3** is cleaved by: a) C3bB b) C3bBb c) Factor B d) Factor D e) Factor H **Answer: b) C3bBb** **Explanation:** **C3bBb** is the **C3 convertase** of the **alternative pathway** that cleaves **C3** into **C3a** and **C3b**. ### Question 9 The **membrane attack complex** in the **complement pathway** consists of: a) C3b3b, Bb b) C5b,6,7,8,9 c) Colicins d) OH e) Properdin **Answer: b) C5b,6,7,8,9** **Explanation:** The **membrane attack complex (MAC)** is formed by **complement components C5b, C6, C7, C8, and C9**. ### Question 10 **Acute inflammation** can be initiated by: a) An increase in vascular permeability b) C3 c) Influx of neutrophils d) Lysozyme e) **Mast cell activation** **Answer: e) Mast cell activation** **Explanation:** **Mast cell activation** releases **inflammatory mediators** like **histamine**, which initiate **acute inflammation**. ### Question 11 **Clonal selection** occurs when **antigen** is encountered by: a) Basophils b) Eosinophils c) Mast cells d) Neutrophils e) **T-cell** **Answer: e) T-cell** **Explanation:** **Clonal selection** is the process where specific **T cells** that recognize a particular **antigen** are selected for **proliferation**. ### Question 12 **Complement component C3b**: a) Directly injures bacteria b) Is an anaphylatoxin c) Is chemotactic d) Is the inactive form of C3 e) **Opsonizes bacteria** **Answer: e) Opsonizes bacteria** **Explanation:** **C3b** is a major **opsonin** that coats **bacteria**, marking them for **phagocytosis** by **immune cells**. ### Question 13 **Naturally acquired active im