Exam questions 18, 19

Question 1

Innate immune cell types and roles

Answer 1

Macrophages: Phagocytose microbes and debris, present antigens, and release cytokines. Dendritic cells: Capture and process antigens, present antigens to T cells, linking innate and adaptive immunity. Neutrophils: Phagocytose pathogens and release bactericidal substances. NK cells: Kill virus-infected and cancerous cells via lytic granules. Mast cells: Release histamine and other inflammatory mediators, promoting allergic reactions and parasitic defense.

Question 2

Complement system activation pathways

Answer 2

Classical: C1q binds antibody-antigen complexes. Lectin: Mannose-binding lectin binds microbial carbohydrates. Alternative: Spontaneous C3 hydrolysis or C3b binding to pathogens.

Question 3

C5 cleavage in complement system

Answer 3

C5a: Inflammatory mediator, recruits immune cells. C5b: Initiates membrane attack complex (MAC) formation, leading to pathogen lysis.

Question 4

Pattern-recognition receptors (PRRs) families

Answer 4

TLRs, NLRs, CLRs, RLRs, CDSs.

Question 5

PRRs sensing double-stranded RNA

Answer 5

RIG-I/MDA5: Cytosolic, signals through MAVS, induces IFN-β and antiviral responses. TLR3: Endosomal, signals through TRIF, induces IFN-β and antiviral responses.

Question 6

Naïve CD4+ T helper cell activation

Answer 6

Antigen-presenting cells present antigens via MHC II to CD4+ T cells, initiating signaling through TCR and CD4 co-receptor.

Question 7

CD4+ T cell subsets and cytokines

Answer 7

IL-12 + IFN-γ: Th1 IL-6 + IL-23: Th17 IL-4: Th2 TGF-β + IL-2: Treg IL-6: Tfh

Question 8

Main functions of CD4+ T helper subsets

Answer 8

Th1: Activates macrophages, fights intracellular pathogens. Th17: Inflammation, defense against bacteria and fungi. Th2: Helps in parasitic immunity and antibody production. Treg: Suppresses immune responses, maintains tolerance. Tfh: Supports B cell activation and antibody production.

Question 9

Licensing dendritic cells to activate CD8+ T cells

Answer 9

Dendritic cells present extracellular antigens via MHC I, providing co-stimulatory signals to activate CD8+ T cells.

Question 10

Viral evasion via TAP inhibition

Answer 10

Inhibition of TAP prevents MHC I antigen presentation, impairing CD8+ T cell activation, but enhances NK cell-mediated killing.

Question 11

Cytotoxic T cells, NK cells, NKT cells recognition

Answer 11

Cytotoxic T cells: Recognize antigens on MHC I. NK cells: Detect absence of MHC I or antibody-coated targets. NKT cells: Recognize lipid antigens presented on CD1d.

Question 12

V(D)J recombination enzymes

Answer 12

RAG1/2: Initiates recombination at signal sequences. TdT: Adds random nucleotides, increasing diversity.

Question 13

Follicular B2 cell activation and linked-recognition

Answer 13

B2 cells bind antigen, present it on MHC II to T helper cells. Linked-recognition requires T cell and B cell to recognize the same antigen.

Question 14

AID processes and antibody effects

Answer 14

Somatic hypermutation (SHM): Introduces mutations in variable region, improving affinity. Class switch recombination (CSR): Changes antibody isotype for specialized functions.

Question 15

Antibody isotypes

Answer 15

IgM, IgD, IgG, IgA, IgE.

Question 16

Antibodies promoting phagocytosis

Answer 16

Antibodies activate complement (C3b), opsonize microbes for phagocyte recognition.

Question 17

FcεRI signaling mutation effects

Answer 17

Impaired IgE signaling increases susceptibility to parasitic infections and reduces allergic reactions.

Question 18

Monoclonal vs polyclonal antibodies

Answer 18

Monoclonal: Specific to one epitope, from a single B cell clone. Polyclonal: Recognize multiple epitopes, from multiple B cells.

Question 19

Secondary/acquired immunodeficiency

Answer 19

Caused by external factors, such as infections (e.g., HIV) or cancer.

Question 20

Herd immunity

Answer 20

Protection occurs when a large portion of the population is immune, reducing disease spread.

Question 21

Immune response phases toward infection

Answer 21

Innate: Rapid, involves antimicrobial proteins, phagocytes, complement, and NK cells. Adaptive: Involves T and B cell activation, differentiation into effector cells, and memory formation.

Question 22

Phagocytosis process and phagocytes

Answer 22

Phagocytosis: Engulfing pathogens into phagosomes for degradation. Neutrophils: Rapid responders, kill pathogens via granules. Macrophages: Resident cells, phagocytose pathogens, present antigens.

Question 23

Role of C3 in immune response

Answer 23

C3 is essential for complement activation, opsonization, inflammation, and pathogen lysis. C3 deficiency: Increased susceptibility to bacterial infections and inability to form MAC.

Question 24

Dendritic cells bridging innate and adaptive immunity

Answer 24

Dendritic cells capture pathogens and present antigens to T cells, providing co-stimulatory signals to initiate adaptive immunity.

Question 25

MHC I and MHC II expression and antigen loading

Answer 25

MHC I: Expressed on all nucleated cells, presents intracellular antigens to CD8+ T cells. MHC II: Expressed on professional APCs, presents extracellular antigens to CD4+ T cells.

Question 26

Positive selection of thymocytes and self-MHC restriction

Answer 26

Positive selection: Thymocytes that bind self-MHC with moderate affinity survive and differentiate. Self-MHC restriction: T cells recognize antigens only when presented by self-MHC molecules.

Question 27

AIRE mutation and autoimmune disorders

Answer 27

AIRE allows tissue-specific antigen presentation in the thymus for self-tolerance. Its loss leads to autoimmune diseases.

Question 28

HIV infection and CD4+ T cell loss

Answer 28

Loss of CD4+ T cells impairs adaptive immunity, leading to susceptibility to infections and loss of effective immune responses.

Question 29

Th1 characteristics and role in immune response

Answer 29

Induced by IL-12 and IFN-γ, Th1 cells produce IFN-γ, activating macrophages for intracellular pathogen destruction.

Question 30

Hematopoietic stem cells

Answer 30

Hematopoietic stem cells give rise to all blood cells, with self-renewal and multipotency abilities.

Question 31

Antibody diversity in B2 cells

Answer 31

Combinatorial diversity, heavy-light chain pairing, P-nucleotide addition, exonuclease trimming, N-nucleotide addition by TdT.

Question 32

Class-switch rearrangement importance

Answer 32

Enables antibodies to perform specialized functions by switching isotypes like IgG, IgA, and IgE.

Question 33

IgM vs IgA structure and function

Answer 33

IgM: Pentameric, efficient complement activation, cannot cross placenta. IgA: Predominant in mucosal secretions, neutralizes pathogens without complement activation.

Question 34

Types of vaccines and their advantages/disadvantages

Answer 34

Live attenuated: Pro - Strong immune response, fewer boosters. Con - Risk of reversion. Inactivated: Pro - Safe, stable storage. Con - Requires boosters, weak cell-mediated immunity. Subunit: Pro - Safe, stable. Con - Requires adjuvants and boosters.