Lecture 35

Question 1

Which Immunoglobulins are determined by Alternative RNA splicing

Answer 1

IgM to IgD

Question 2

Which Immunoglobulins are determined by Class switching

Answer 2

IgA, IgE, and IgG
(from IgM or IgD)

Question 3

Function of antibodies

Answer 3

Mediate the clearance and destruction of pathogen in a variety of ways (depending on each antibody isotype)

Question 4

Key antibody functions

Answer 4

1) Neutralization
2) Opsonization
3) Complement fixation/initiated complement
4) Antibody-dependent cell-mediated cytotoxicity (ADCC) (including NK cells inducing apoptosis)
5) Degranulation similar to ADCC
6) Transport

Question 5

How do Igs opsonize, act on cells, and get across cells

Answer 5

By Fc receptors (FcR)

Question 6

Which cells are transmembrane receptors that bind to Fc portions of Igs found

Answer 6

Expressed on macrophages, granulocytes, dendritic cells, mast cells, B cells, epithelial cells

Question 7

How do transmembrane receptors bind to Fc portion of Igs

Answer 7

In a Class specific manner
FcgammaRI binds to IgG1
FcepsilonRI binds to IgE

Question 8

Which effector function of antibodies do Fc receptors mediate

Answer 8

Crosslinking FcR to trigger signaling

Question 9

What is crosslinking

Answer 9

When more than 1 Fc receptor binds to an antibody that is bound to an antigen
No crosslinking–>no intracellular signaling

Question 10

Functions of Fc receptors

Answer 10

1) Degranulation
2) Opsonization
3) Transportation and maintenance of serum levels
4) ADCC

Question 11

Benefit of using FcRs

Answer 11

Allows non-specific immune cells to take advantage of antigen-specific antibodies

Question 12

Main action of Opsonization

Answer 12

Promotes and/or enhances the engulfment of antigens by phagocytes

Question 13

IgG different subclass effector functions

Answer 13

1) Effective complement fixation
2) Good at mediating ADCC by NK cells

Question 14

Effector function shared by ALL IgG variants

Answer 14

Enhance phagocytosis by macrophages–>opsonization

Question 15

Main action of antibody-dependent cell-mediated cytotoxicity (ADCC)

Answer 15

Activates the killing activity of several types cytotoxic cells (ex. NK cells)

Question 16

Which Fc receptors do NK cells

Answer 16

NK cells have FcgammaRs (recognize Fc region of IgG antibodies)

Question 17

Pathway of ADCC

Answer 17

FcgammaRs on NK cells bind to Fc region of IgG antibodies–>crosslinking triggers signaling–>NK cell releases toxic granules (same in ADCC and innate)–>target cell dies by apoptosis

Question 18

Which immunoglobulin is best known for role in allergy and asthma

Answer 18

IgE

Question 19

Which Immunoglobulin plays a role in protection against parasitic helminths and protozoa

Answer 19

IgE

Question 20

IgE effector function

Answer 20

1) Degranulation of eosinophils/basophils
2) Release of molecules such as histamine to damage large pathogens

Question 21

Main action of Neutralization

Answer 21

Protects against viral or bacterial infection, or against the damaging effects of toxins

Question 22

Targets for Neutralization

Answer 22

Toxins, Viruses, Bacteria

Question 23

Which antibodies/Igs are most important for neutralization

Answer 23

IgG and IgA

Question 24

Mechanism of Neutralization

Answer 24

Bind antibodies to toxins or pathogen to prevent them from binding their targets and exerting their effects

Question 25

Where is IgA found

Answer 25

Secretions and mucosal tissues 1) Mucus in gut 2) Milk in mammary glands 3) Tears 4) Saliva

Question 26

Outcome of Complement activation

Answer 26

Generation of membrane attack complex (MAC), inflammation and/or opsonization

Question 27

What does C1q bind to

Answer 27

C1q binds pathogen surface 1) Can bind pathogen directly 2) Can binds antibodies that are bound to pathogen surface

Question 28

What does C1q binding trigger

Answer 28

Signaling cascade on pathogen surface C3 convertase is generated C3 cleaved-->C3a and C3b

Question 29

Which Igs trigger the complement cascade

Answer 29

IgG and IgM, but IgM is the most effective

Question 30

What is IgM effective at

Answer 30

1) Activating the complement cascade 2) Forming dense antibodies pathogen complexes that are efficiently engulfed by macrophage

Question 31

Where is IgE found

Answer 31

Near epithelial surfaces

Question 32

Where is IgG found

Answer 32

Widely distributed In newborn circulation (maternal IgG, passive immunity)

Question 33

Where is IgD found

Answer 33

Blood but at higher levels in secretion of upper respiratory tract

Question 34

Effector functions of IgD

Answer 34

Binds basophils and mast cells promoting them to release antimicrobial peptides (AMPs), cytokines, and chemokines