PCB 3233 Immunology - Exam 1-4
Comprehensive Study Guide
Exam 1: Innate Immunity & Fundamentals
1. What are the three main functions of the immune system?
Answer: Defense against pathogens, surveillance and elimination of malignant cells (cancer),
and removal of dead/damaged cells and tissues.
2. Differentiate between innate and adaptive immunity by time of response and specificity.
Answer: Innate immunity responds immediately (hours) but is non-specific, using generic
pattern recognition. Adaptive immunity responds with a delay (days), is highly specific to
antigens, and creates immunological memory.
3. What are Pathogen-Associated Molecular Patterns (PAMPs)? Give two examples.
Answer: PAMPs are conserved molecular structures shared by broad classes of microbes.
Examples: Lipopolysaccharide (LPS) in gram-negative bacteria, and double-stranded RNA
(dsRNA) in viruses.
4. Which cells are considered the principal "professional" phagocytes?
Answer: Neutrophils, monocytes (in blood), and macrophages (in tissues). Dendritic cells are
also phagocytic but are more specialized for antigen presentation.
5. What is the primary role of dendritic cells in initiating an adaptive immune response?
Answer: To capture, process, and present antigen via MHC molecules to naïve T cells in the
secondary lymphoid organs, thereby activating them. This is the critical link between innate and
adaptive immunity.
6. Describe the process of extravasation (diapedesis).
Answer: It is the multi-step process by which leukocytes exit the bloodstream and enter
inflamed tissue. Steps: Rolling (mediated by selectins), activation (by chemokines), firm
adhesion (mediated by integrins), and transendothelial migration.
7. What is the main function of the complement membrane attack complex (MAC)?
Answer: To form a pore (C5b-6789) in the membrane of pathogens, leading to osmotic lysis and
death.
8. What are the three pathways of complement activation?
Answer: The Classical Pathway (activated by antibody-antigen complexes), the Lectin Pathway
,(activated by mannose-binding lectin binding to microbial sugars), and the Alternative Pathway
(spontaneous, antibody-independent).
9. Which cytokine is a key endogenous pyrogen (causes fever)?
Answer: Interleukin-1β (IL-1β), along with TNF-α and IL-6.
10. What is opsonization, and which complement component is a key opsonin?
Answer: Opsonization is the coating of a pathogen by molecules (opsonins) to enhance
phagocytosis. C3b is the key complement-derived opsonin.
11. Where do all hematopoietic cells originate from?
Answer: The bone marrow, from a common pluripotent hematopoietic stem cell (HSC).
12. Which pattern recognition receptors (PRRs) are found in endosomal membranes and
detect viral nucleic acids?
Answer: Toll-like receptors 3 (dsRNA), 7/8 (ssRNA), and 9 (unmethylated CpG DNA).
13. What is the role of acute-phase proteins like C-reactive protein (CRP)?
Answer: CRP acts as an opsonin by binding to phosphocholine on microbial surfaces and
activating the complement classical pathway.
14. What is inflammasome, and what does it produce?
Answer: A multi-protein intracellular complex that activates caspase-1, which cleaves pro-IL-1β
into its active, secreted form (IL-1β).
15. NK cells kill virus-infected cells. How do they recognize "self" vs. "altered self"?
Answer: Through a balance of inhibitory receptors (that recognize self-MHC Class I) and
activating receptors (that recognize stress-induced ligands). Missing self-MHC I (downregulated
by some viruses) releases the inhibitory signal, triggering killing.
Exam 2: Adaptive Immunity - B Cells & Antibodies
16. What is the primary immunological function of antibodies (immunoglobulins)?
Answer: To bind specifically to antigens, leading to their neutralization and marking them for
elimination by other immune mechanisms (opsonization, complement activation, ADCC).
17. Describe the basic structure of an immunoglobulin monomer.
Answer: Composed of two identical heavy chains and two identical light chains, held together
by disulfide bonds. Each chain has constant and variable regions. The variable regions form the
antigen-binding site (Fab), while the constant region (Fc) mediates effector functions.
18. What is isotype switching (class switching), and what cytokine drives a switch to IgE?
Answer: The process by which a B cell changes the constant region of its antibody heavy chain
,(e.g., from IgM to IgG, IgA, IgE) while retaining the same antigen specificity. IL-4 and IL-13 drive
switching to IgE.
19. Where do B cells primarily mature?
Answer: In the bone marrow.
20. What is the difference between a B cell receptor (BCR) and the antibody it later secretes?
Answer: The BCR is a membrane-bound form of the antibody, with a transmembrane domain.
The secreted antibody is the soluble form of the same protein, lacking the transmembrane
domain.
21. What process generates the enormous diversity of antibody variable regions?
Answer: Somatic recombination of Variable (V), Diversity (D, for heavy chains), and Joining (J)
gene segments during B cell development in the bone marrow.
22. What are the two primary functions of secreted IgM?
Answer: 1) It is the first antibody produced in a primary response. 2) It is a potent activator of
the complement classical pathway due to its pentameric structure.
23. Which antibody isotype is most abundant in serum and provides long-term immunity?
Answer: IgG.
24. Which antibody isotype is associated with mucosal immunity and is secreted across
epithelial layers?
Answer: IgA (particularly dimeric IgA).
25. What is affinity maturation, and where does it occur?
Answer: The process by which B cells producing antibodies with higher affinity for the antigen
are selectively expanded during an immune response. It occurs in the germinal centers of
secondary lymphoid organs.
26. What is a T-dependent B cell response?
Answer: A B cell response to protein antigens that requires help from CD4+ T helper (Th) cells.
This leads to isotype switching, affinity maturation, and memory cell formation.
27. What role does CD40L (on T cells) play in B cell activation?
Answer: It binds CD40 on the B cell, providing a critical co-stimulatory signal required for B cell
proliferation, isotype switching, and germinal center formation.
28. What is a neutralizing antibody?
Answer: An antibody that binds to a pathogen (e.g., a virus) and directly blocks its ability to
infect a host cell.
, 29. What is the difference between a primary and secondary antibody response?
Answer: The primary response is slower, with a peak in IgM followed by lower-affinity IgG. The
secondary response (upon re-exposure) is faster, more robust, and consists of high-affinity IgG
and memory cells.
30. What is the role of plasma cells?
Answer: They are terminally differentiated B cells that are antibody "factories," secreting large
quantities of a single specific antibody. They reside in the bone marrow and spleen.
Exam 3: Adaptive Immunity - T Cells & MHC
31. What is the defining function of a T cell receptor (TCR) compared to a BCR?
Answer: The TCR recognizes antigen ONLY when it is presented as a peptide fragment bound to
an MHC molecule on an antigen-presenting cell (APC). The BCR recognizes free, intact antigen.
32. Where do T cells mature and undergo positive and negative selection?
Answer: In the thymus.
33. What are the two main classes of MHC molecules, and which T cell subset does each one
present antigen to?
Answer: MHC Class I presents to CD8+ cytotoxic T cells (CTLs). MHC Class II presents to CD4+ T
helper (Th) cells.
34. What is the source of peptides loaded onto MHC Class I vs. MHC Class II molecules?
Answer: MHC Class I: Peptides are derived from endogenous/cytoplasmic proteins (e.g., viral
proteins, self-proteins) processed via the proteasome. MHC Class II: Peptides are derived from
exogenous/engulfed proteins (e.g., bacteria) processed in the endolysosomal pathway.
35. What is the function of CD4 and CD8 co-receptors?
Answer: CD4 binds to MHC Class II, stabilizing the TCR-MHC interaction and delivering
intracellular signals. CD8 binds to MHC Class I, serving the same function for CTLs.
36. What is the critical signal required for T cell activation beyond TCR engagement (Signal 1)?
Answer: Signal 2 is co-stimulation, most critically the binding of B7 (CD80/86) on the APC to
CD28 on the T cell. Without Signal 2, the T cell becomes anergic.
37. What is the function of CD8+ Cytotoxic T Lymphocytes (CTLs)?
Answer: To directly kill virus-infected cells, tumor cells, or allografts by inducing apoptosis via
perforin/granzyme and Fas/FasL pathways.
Comprehensive Study Guide
Exam 1: Innate Immunity & Fundamentals
1. What are the three main functions of the immune system?
Answer: Defense against pathogens, surveillance and elimination of malignant cells (cancer),
and removal of dead/damaged cells and tissues.
2. Differentiate between innate and adaptive immunity by time of response and specificity.
Answer: Innate immunity responds immediately (hours) but is non-specific, using generic
pattern recognition. Adaptive immunity responds with a delay (days), is highly specific to
antigens, and creates immunological memory.
3. What are Pathogen-Associated Molecular Patterns (PAMPs)? Give two examples.
Answer: PAMPs are conserved molecular structures shared by broad classes of microbes.
Examples: Lipopolysaccharide (LPS) in gram-negative bacteria, and double-stranded RNA
(dsRNA) in viruses.
4. Which cells are considered the principal "professional" phagocytes?
Answer: Neutrophils, monocytes (in blood), and macrophages (in tissues). Dendritic cells are
also phagocytic but are more specialized for antigen presentation.
5. What is the primary role of dendritic cells in initiating an adaptive immune response?
Answer: To capture, process, and present antigen via MHC molecules to naïve T cells in the
secondary lymphoid organs, thereby activating them. This is the critical link between innate and
adaptive immunity.
6. Describe the process of extravasation (diapedesis).
Answer: It is the multi-step process by which leukocytes exit the bloodstream and enter
inflamed tissue. Steps: Rolling (mediated by selectins), activation (by chemokines), firm
adhesion (mediated by integrins), and transendothelial migration.
7. What is the main function of the complement membrane attack complex (MAC)?
Answer: To form a pore (C5b-6789) in the membrane of pathogens, leading to osmotic lysis and
death.
8. What are the three pathways of complement activation?
Answer: The Classical Pathway (activated by antibody-antigen complexes), the Lectin Pathway
,(activated by mannose-binding lectin binding to microbial sugars), and the Alternative Pathway
(spontaneous, antibody-independent).
9. Which cytokine is a key endogenous pyrogen (causes fever)?
Answer: Interleukin-1β (IL-1β), along with TNF-α and IL-6.
10. What is opsonization, and which complement component is a key opsonin?
Answer: Opsonization is the coating of a pathogen by molecules (opsonins) to enhance
phagocytosis. C3b is the key complement-derived opsonin.
11. Where do all hematopoietic cells originate from?
Answer: The bone marrow, from a common pluripotent hematopoietic stem cell (HSC).
12. Which pattern recognition receptors (PRRs) are found in endosomal membranes and
detect viral nucleic acids?
Answer: Toll-like receptors 3 (dsRNA), 7/8 (ssRNA), and 9 (unmethylated CpG DNA).
13. What is the role of acute-phase proteins like C-reactive protein (CRP)?
Answer: CRP acts as an opsonin by binding to phosphocholine on microbial surfaces and
activating the complement classical pathway.
14. What is inflammasome, and what does it produce?
Answer: A multi-protein intracellular complex that activates caspase-1, which cleaves pro-IL-1β
into its active, secreted form (IL-1β).
15. NK cells kill virus-infected cells. How do they recognize "self" vs. "altered self"?
Answer: Through a balance of inhibitory receptors (that recognize self-MHC Class I) and
activating receptors (that recognize stress-induced ligands). Missing self-MHC I (downregulated
by some viruses) releases the inhibitory signal, triggering killing.
Exam 2: Adaptive Immunity - B Cells & Antibodies
16. What is the primary immunological function of antibodies (immunoglobulins)?
Answer: To bind specifically to antigens, leading to their neutralization and marking them for
elimination by other immune mechanisms (opsonization, complement activation, ADCC).
17. Describe the basic structure of an immunoglobulin monomer.
Answer: Composed of two identical heavy chains and two identical light chains, held together
by disulfide bonds. Each chain has constant and variable regions. The variable regions form the
antigen-binding site (Fab), while the constant region (Fc) mediates effector functions.
18. What is isotype switching (class switching), and what cytokine drives a switch to IgE?
Answer: The process by which a B cell changes the constant region of its antibody heavy chain
,(e.g., from IgM to IgG, IgA, IgE) while retaining the same antigen specificity. IL-4 and IL-13 drive
switching to IgE.
19. Where do B cells primarily mature?
Answer: In the bone marrow.
20. What is the difference between a B cell receptor (BCR) and the antibody it later secretes?
Answer: The BCR is a membrane-bound form of the antibody, with a transmembrane domain.
The secreted antibody is the soluble form of the same protein, lacking the transmembrane
domain.
21. What process generates the enormous diversity of antibody variable regions?
Answer: Somatic recombination of Variable (V), Diversity (D, for heavy chains), and Joining (J)
gene segments during B cell development in the bone marrow.
22. What are the two primary functions of secreted IgM?
Answer: 1) It is the first antibody produced in a primary response. 2) It is a potent activator of
the complement classical pathway due to its pentameric structure.
23. Which antibody isotype is most abundant in serum and provides long-term immunity?
Answer: IgG.
24. Which antibody isotype is associated with mucosal immunity and is secreted across
epithelial layers?
Answer: IgA (particularly dimeric IgA).
25. What is affinity maturation, and where does it occur?
Answer: The process by which B cells producing antibodies with higher affinity for the antigen
are selectively expanded during an immune response. It occurs in the germinal centers of
secondary lymphoid organs.
26. What is a T-dependent B cell response?
Answer: A B cell response to protein antigens that requires help from CD4+ T helper (Th) cells.
This leads to isotype switching, affinity maturation, and memory cell formation.
27. What role does CD40L (on T cells) play in B cell activation?
Answer: It binds CD40 on the B cell, providing a critical co-stimulatory signal required for B cell
proliferation, isotype switching, and germinal center formation.
28. What is a neutralizing antibody?
Answer: An antibody that binds to a pathogen (e.g., a virus) and directly blocks its ability to
infect a host cell.
, 29. What is the difference between a primary and secondary antibody response?
Answer: The primary response is slower, with a peak in IgM followed by lower-affinity IgG. The
secondary response (upon re-exposure) is faster, more robust, and consists of high-affinity IgG
and memory cells.
30. What is the role of plasma cells?
Answer: They are terminally differentiated B cells that are antibody "factories," secreting large
quantities of a single specific antibody. They reside in the bone marrow and spleen.
Exam 3: Adaptive Immunity - T Cells & MHC
31. What is the defining function of a T cell receptor (TCR) compared to a BCR?
Answer: The TCR recognizes antigen ONLY when it is presented as a peptide fragment bound to
an MHC molecule on an antigen-presenting cell (APC). The BCR recognizes free, intact antigen.
32. Where do T cells mature and undergo positive and negative selection?
Answer: In the thymus.
33. What are the two main classes of MHC molecules, and which T cell subset does each one
present antigen to?
Answer: MHC Class I presents to CD8+ cytotoxic T cells (CTLs). MHC Class II presents to CD4+ T
helper (Th) cells.
34. What is the source of peptides loaded onto MHC Class I vs. MHC Class II molecules?
Answer: MHC Class I: Peptides are derived from endogenous/cytoplasmic proteins (e.g., viral
proteins, self-proteins) processed via the proteasome. MHC Class II: Peptides are derived from
exogenous/engulfed proteins (e.g., bacteria) processed in the endolysosomal pathway.
35. What is the function of CD4 and CD8 co-receptors?
Answer: CD4 binds to MHC Class II, stabilizing the TCR-MHC interaction and delivering
intracellular signals. CD8 binds to MHC Class I, serving the same function for CTLs.
36. What is the critical signal required for T cell activation beyond TCR engagement (Signal 1)?
Answer: Signal 2 is co-stimulation, most critically the binding of B7 (CD80/86) on the APC to
CD28 on the T cell. Without Signal 2, the T cell becomes anergic.
37. What is the function of CD8+ Cytotoxic T Lymphocytes (CTLs)?
Answer: To directly kill virus-infected cells, tumor cells, or allografts by inducing apoptosis via
perforin/granzyme and Fas/FasL pathways.
