Immune responses – humoral, cell-mediated, complement system - Question Bank

1. The alternative pathway's C3 convertase is formed by which components?
A) C4b2a
B) C3bBb
C) C1q, C1r, C1s
D) C5b, C6, C7
2. Which cellular component is directly involved in the recognition of antigens by T lymphocytes?
A) Antibodies
B) T cell receptor (TCR)
C) B cell receptor (BCR)
D) Major Histocompatibility Complex (MHC) molecules
3. What distinguishes adaptive immunity (humoral and cell-mediated) from innate immunity?
A) Adaptive immunity is non-specific.
B) Adaptive immunity has memory and is highly specific.
C) Innate immunity has memory.
D) Adaptive immunity lacks diversity.
4. Which antibody isotype is most effective at activating the classical complement pathway?
A) IgM and IgG
B) IgA
C) IgE
D) IgD
5. What is the function of the anaphylatoxins (C3a, C5a) generated during complement activation?
A) To directly lyse pathogen membranes
B) To enhance phagocytosis by opsonization
C) To promote inflammation by increasing vascular permeability and attracting leukocytes
D) To neutralize toxins
6. Which immune response is primarily responsible for clearing intracellular pathogens like viruses and some intracellular bacteria?
A) Humoral immunity
B) Innate immunity
C) Cell-mediated immunity
D) Complement system activation only
7. What is the role of perforin, released by cytotoxic T lymphocytes?
A) To signal apoptosis to the target cell
B) To form pores in the target cell membrane, allowing granzymes to enter
C) To bind to MHC class I molecules
D) To enhance phagocytosis by macrophages
8. The formation of the C3 convertase enzyme is critical for amplifying the complement cascade. Which components form the C3 convertase in the classical and lectin pathways?
A) C4b2a
B) C3bBb
C) C1q, C1r, C1s, C4, C2
D) C5b, C6, C7, C8, C9
9. Which of the following is a key characteristic of humoral immunity?
A) It is mediated by T lymphocytes.
B) It relies on antibodies produced by B lymphocytes.
C) It primarily targets intracellular pathogens.
D) It involves the direct killing of target cells by immune cells.
10. What is the primary function of antibodies in preventing viral infections?
A) To kill virus-infected cells directly
B) To prevent viruses from binding to host cell receptors
C) To activate the complement system to lyse viruses
D) To induce fever in the host
11. Which pathway of complement activation involves the direct binding of complement proteins to the surface of a pathogen in the absence of antibodies or lectins?
A) Classical pathway
B) Alternative pathway
C) Lectin pathway
D) Terminal pathway
12. Which specific type of T cell is responsible for downregulating immune responses to prevent excessive inflammation or autoimmunity?
A) Cytotoxic T cell
B) T helper cell
C) Regulatory T cell (Treg)
D) Memory T cell
13. What is the role of plasma cells in humoral immunity?
A) To present antigens to T helper cells
B) To directly kill infected cells
C) To differentiate into memory B cells
D) To produce and secrete large amounts of antibodies
14. Which of the following describes the function of the complement system in lysis?
A) It coats pathogens to enhance phagocytosis.
B) It triggers inflammation by releasing anaphylatoxins.
C) It forms the Membrane Attack Complex (MAC) that creates pores in pathogen membranes.
D) It neutralizes bacterial toxins.
15. The process of generating a large number of identical B cells or T cells that are specific for a particular antigen is called:
A) Apoptosis
B) Clonal selection and expansion
C) Phagocytosis
D) Opsonization
16. Which immune cells are essential for recognizing and presenting antigens on MHC class I molecules to cytotoxic T cells?
A) B cells
B) Dendritic cells and all nucleated cells
C) Erythrocytes
D) Platelets
17. What is the biological significance of antibodies binding to bacterial toxins?
A) They enhance the toxicity of the toxins.
B) They neutralize the toxins, preventing them from harming host cells.
C) They mark the toxins for destruction by NK cells.
D) They trigger the release of inflammatory mediators.
18. Which complement pathway is considered part of the innate immune system and can be activated independently of antibodies?
A) Classical pathway
B) Lectin pathway and Alternative pathway
C) Terminal pathway
D) Antibody-dependent pathway
19. What is the role of antigen-presenting cells (APCs) like macrophages and dendritic cells in cell-mediated immunity?
A) To directly kill infected cells
B) To produce antibodies
C) To process and present antigens to T lymphocytes
D) To suppress the immune response
20. Cell-mediated immunity is particularly important for defense against:
A) Extracellular bacteria
B) Free viruses and extracellular parasites
C) Intracellular pathogens like viruses and some bacteria
D) Toxins produced by bacteria
21. Which of the following is a function of C3b, a cleavage product of C3?
A) Inducing inflammation
B) Forming the MAC
C) Acting as an opsonin to promote phagocytosis
D) Cleaving C5
22. What is the key difference between primary and secondary immune responses?
A) Primary response is faster and stronger due to memory cells.
B) Secondary response is slower and weaker.
C) Primary response involves only innate immunity.
D) Secondary response does not involve antibodies.
23. In humoral immunity, what is the fate of a B cell that encounters its specific antigen and receives co-stimulatory signals from a T helper cell?
A) It undergoes apoptosis immediately.
B) It differentiates into a plasma cell and/or a memory B cell.
C) It becomes a cytotoxic T lymphocyte.
D) It migrates to the thymus for maturation.
24. Which component of the complement system is central to all three activation pathways and its cleavage generates fragments with critical functions?
A) C1q
B) C3
C) C5
D) C9
25. What is the role of cytokines in immune responses?
A) To directly bind and neutralize toxins
B) To act as signaling molecules that regulate immune cell activity and communication
C) To form the Membrane Attack Complex (MAC)
D) To present antigens to T cells
26. Which immune cells are primarily responsible for recognizing and killing cells that are infected with viruses or are cancerous, especially those lacking MHC class I expression?
A) B lymphocytes
B) T helper cells
C) Plasma cells
D) Natural Killer (NK) cells
27. What is the primary outcome of complement activation via the classical, alternative, or lectin pathways?
A) Production of memory B cells
B) Release of cytokines
C) Cleavage of C3 into C3a and C3b
D) Direct killing of virus-infected cells
28. Which immunoglobulin is involved in allergic reactions and defense against parasitic worms?
A) IgG
B) IgA
C) IgM
D) IgE
29. The complement system's role in enhancing phagocytosis is known as:
A) Lysis
B) Opsonization
C) Inflammation
D) Chemotaxis
30. Which type of T cell is responsible for recognizing and responding to antigens presented on MHC class II molecules?
A) Cytotoxic T lymphocyte (CD8+)
B) Regulatory T cell (Treg)
C) T helper cell (CD4+)
D) Natural Killer (NK) cell
31. What is the term for the process where antibodies bind to antigens, preventing the pathogen from infecting host cells?
A) Opsonization
B) Complement fixation
C) Neutralization
D) Agglutination
32. Which enzyme complex cleaves C5 to initiate the formation of the Membrane Attack Complex (MAC)?
A) C3 convertase
B) C5 convertase
C) C1 inhibitor
D) Properdin
33. What is the main function of MHC class II molecules in adaptive immunity?
A) Present intracellular antigens to cytotoxic T cells
B) Present extracellular antigens (e.g., bacterial peptides) to T helper cells
C) Activate the classical complement pathway
D) Induce B cell proliferation
34. Which antibody isotype is predominantly found in mucosal secretions like saliva, tears, and breast milk?
A) IgG
B) IgM
C) IgA
D) IgE
35. The alternative pathway of complement activation is unique because it can be triggered without the involvement of antibodies. What initiates it?
A) Mannose-binding lectin
B) Antibody-antigen complexes
C) Spontaneous C3 hydrolysis or direct interaction with pathogen surfaces
D) Lysozyme binding
36. What is the primary mechanism by which cytotoxic T lymphocytes (CTLs) induce apoptosis in target cells?
A) Releasing histamine
B) Producing antibodies
C) Releasing perforin and granzymes
D) Activating the complement system
37. Memory cells are crucial for adaptive immunity. Which cell type is primarily responsible for long-term immunological memory in humoral immunity?
A) Plasma cells
B) Effector T helper cells
C) Memory B cells
D) Mast cells
38. Which complement protein acts as a potent anaphylatoxin, promoting inflammation and attracting immune cells?
A) C1q
B) C3a and C5a
C) C5b
D) Factor B
39. What is the role of MHC class I molecules in cell-mediated immunity?
A) Present extracellular antigens to T helper cells
B) Present intracellular antigens (e.g., viral peptides) to cytotoxic T cells
C) Present antigens to B cells for antibody production
D) Bind to complement proteins to initiate lysis
40. Which of the following is a characteristic feature of cell-mediated immunity?
A) Involves soluble antibodies in the bloodstream
B) Primarily targets extracellular pathogens
C) Mediated by T lymphocytes
D) Leads to the formation of memory B cells
41. The lectin pathway of complement activation is triggered by the binding of mannose-binding lectin (MBL) to microbial carbohydrates. What is MBL?
A) An antibody
B) A type of cytokine
C) A pattern recognition molecule
D) A phagocytic cell
42. Opsonization, a process that enhances phagocytosis, is a key function of which immune molecules?
A) Cytokines
B) Antibodies and complement proteins
C) T cell receptors
D) Mast cell degranulators
43. What is the function of regulatory T cells (Treg cells) in cell-mediated immunity?
A) To enhance the immune response against pathogens
B) To suppress the immune response and prevent autoimmunity
C) To produce antibodies against intracellular pathogens
D) To directly kill virus-infected cells
44. Which immunoglobulin (antibody) is the first to be produced during a primary immune response?
A) IgG
B) IgA
C) IgM
D) IgE
45. Which pathway of complement activation is initiated by antigen-antibody complexes?
A) Alternative pathway
B) Lectin pathway
C) Classical pathway
D) Terminal pathway
46. What is the primary role of antibodies in humoral immunity?
A) Directly lyse bacterial cell walls
B) Opsonize pathogens for phagocytosis, neutralize toxins, and activate complement
C) Induce fever and inflammation
D) Suppress the immune response
47. Cytotoxic T lymphocytes (CTLs or CD8+ T cells) are primarily involved in which type of immune response?
A) Humoral immunity
B) Regulation of antibody production
C) Cell-mediated immunity, by killing infected or cancerous cells
D) Complement activation
48. Which component of the complement system is responsible for forming the Membrane Attack Complex (MAC)?
A) C3 convertase
B) C5 convertase
C) C1q
D) C5b, C6, C7, C8, and C9
49. What is the main function of T helper cells (CD4+ T cells) in cell-mediated immunity?
A) Directly killing infected cells
B) Producing antibodies
C) Activating other immune cells like B cells and cytotoxic T cells
D) Phagocytosing pathogens
50. Which type of immune response primarily involves B lymphocytes and the production of antibodies?
A) Cell-mediated immunity
B) Humoral immunity
C) Innate immunity
D) Inflammatory response
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