Effector Responses: Humoral and Cell-mediated Immunity

Question 1

Neutralization

Answer 1

protects against viral or bacteria infection or the damaging effects of toxins

Question 2

Agglutination

Answer 2

enhances neutralization and more efficient clearance of pathogens from the body

Question 3

Opsonization

Answer 3

promotes and or enhances the engulfment of antigens by phagocytosis

Question 4

Complement Activation

Answer 4

result in the generation of the membrane attack complex (MAC), creating pores in pathogen membranes and killing the microbe

Question 5

Antibody-Dependent Cell-mediated Cytotoxicity (ADCC)

Answer 5

activates the killing activity of several types of cytotoxic cells, e.g. NK cells

Question 6

Antibody-Dependent Degranulation and Mediator Release

Answer 6

triggers mediator release from granulocytes

Question 7

What determines an antibody class

Answer 7

constant region determines class, class determines function

Question 8

How an antibody contributes to clearing infection depends on

Answer 8

its class (heavy-chain isotope)

• controls some of its effector function
• determines which receptor can bind
• determines which cells an antibody can activate
• determines which locations in the body it can gain access

Question 9

IgM

Answer 9

• First Ab produced in a primary immune response
• Tends to have lower affinity, high avidity
• Pentavalent (10 Ag binding sites)
• Efficient at complement fixation - MAC formation and target lysis
• Efficient at forming defense Ab-pathogen complexes that are engulfed by macrophages
• Secreted and membrane

Question 10

IgG

Answer 10

• effective at complement fixation
• Mediate ADCC by NK cells
• Enhancing phagocytosis by macrophages
• secreted

Question 11

IgA

Answer 11

• Found in secretion (mucus, milk, tears, saliva)
• effective at neutralizing toxins and pathogens
• Does not fix complement so does not drive inflammation
• protease-resistant, generally has long half-life in secretions
• secreted

Question 12

IgE

Answer 12

• Best known for role in allergy and asthma
• may also play a role in protection against parasitic helminths and protozoa
• Made in very small quantities but induce potent effects
• degranulation of eosinophils/basophils
• release of molecules such as histamine to damage large pathogens
• secreted

Question 13

IgD

Answer 13

• minor immunoglobulin
• present in upper respiratory secretion (respiratory bacterial and viral pathogens)
• binds basophils and mast cells and stimulates release of antimicrobial peptides
• secreted and membrane

Question 14

Fc receptors

Answer 14

mediate many effector functions of Ab

Question 15

FCR signaling

Answer 15

• multiple FcRs need to be cross-linked in order to initiate a signal
• signal may be positive (enhancing) or negative (inhibiting)
• Outcome depends on whether receptor is associated with ITAM or ITIM

Question 16

FC(lambda)R

Answer 16

• most diverse group of FcRs; four families in total
• Main mediator of Ab functions in the body
• Expressed by a wide range of cells
• Most are activating receptors (will induce phagocytosis if expressed by macrophages, will induce degranulation If expressed by cytotoxic cells)

Question 17

Fc(epsilon)R

Answer 17

• Expressed by granulocytes (mast cells/basophils, eosinophils)
• Triggers a signaling cascade that releases histamines, proteases, and other inflammatory mediators
• Most often associated with allergy symptoms

Question 18

PolyIgR

Answer 18

• Polymeric immunoglobulin receptor
• Expressed by epithelial cells
• initiates transport of IgA and IgM from blood to the lumen of multiple tissues (Gastrointestinal tract, respiratory tract, reproductive tract)
• Responsible for carrying Ab into tears and milk and populating gut music with IgA Ab to protect against ingested microbes and toxins

Question 19

Plasma cell-secreted Ab is carried to various body sites for isotope-specific effector function

Answer 19

• opsonizing pathogens for phagocytosis
• Activating complement cascades for pathogen lysis
• Enhancing inflammatory activity of neutrophils
• recruiting cytotoxic cells
• recruiting and activating NK cells or ADCC killing

Question 20

Humoral immunity

Answer 20

• combats pathogens via antibodies
• antibodies produced by B cells
• Antibodies can be transferred between individuals to provide passive immunity

Question 21

Cell-mediated

Answer 21

• involves primarily T lymphocytes

Question 22

CTLs

Answer 22

recognize and kill infected/tumor cells via TCR activation

Question 23

Effector CTL generation from CTL precursors

Answer 23

1- TCR binds peptide presented by APC on MHC class 1
2- Co-stimulatory signal transmitted by CD28-B7 interactions between T cell and APC
3- IL-2, inducing proliferation and differentiation into CTL form

Question 24

CTLs recognize and kill infected or tumor cells by inducing apoptosis in target cells by

Answer 24

1. intrinsic pathway-directional release of cytotoxic granules (perforin/granzyme B)
2. Extrinsic pathway- ligand engagement (Fas-FasL)

Question 25

Perfornin

Answer 25

pore-forming protein

Question 26

Granzyme

Answer 26

serine protease

Question 27

Intrinsic pathway

Answer 27

• When stimulated, CTLs release cytotoxic granule contents
• both proteins are taken up by endocytic processes then punch holes in target cell membranes and induce apoptosis from the inside

Question 28

Extrinsic Pathway

Answer 28

is mediated by the activation of death receptors by extracellular ligands. Engagement of ligand stimulated apoptosis in receptor-bearing cells
- Fas-FasL pathway

Question 29

Missing self model

Answer 29

NK cells recognize and kill infected cells and tumor cells by their absence of MHC class 1

Question 30

How do NK cells recognize target (normal cells)?

Answer 30

• Normal cells present a ligand for the activating (killing) receptor on NK cells and an MHC class 1 ligand for the inhibitory receptors

Question 31

How do NK cells recognize target (viruses)?

Answer 31

When viruses infect cells, some may inhibit MHC class 1 expression to evade detection and elimination by CTLs

Question 32

How do NK cells recognize target (balance)?

Answer 32

the balance of inhibitory vs activating signals determines whether NK is activated or not