Lecture 6: Antibodies and Antigens

Question 1

Antibody structure

Answer 1

2 heavy chains
2 light chains
Chains bound together by disulfide bond & non covalent interactions
Chains have constant and variable regions

Question 2

V and C regions

Answer 2

V region contains Ab binding site

C region determines fate of Ab

Question 3

Antibody cleavage

Answer 3

Antibodies can be cleaved to yield two Fab fragments (Fragment Ag binding site) and an Fc fragment (responsible for effector functions)

Question 4

Cleavage by papain gives

Answer 4

Two Fab fragments and an Fc fragment

Question 5

Cleavage by pepsin

Answer 5

Generates single bivalent Ag binding fragment F(ab’)2

Question 6

Heavy chains and their Ig’s

Answer 6

u (mu) - IgM
S (Delta) - IgD
y (gamma) - IgG
e (epsilon) - IgE
a (alpha) - IgA

Question 7

Light chains

Answer 7

k (kappa)
l (lambda)
Ab unit can only have one, not both

Question 8

H - L chain bonds

Answer 8

Both chains have intrachain disulfide bridges every 90 AAs, creating polypeptide loops

Question 9

Ag binding site in secreted IgG formed by

Answer 9

Juxtaposition of Variable light and Variable heavy domains

Question 10

Difference b/w membrane bound IgM and secreted IgG

Answer 10

Membrane IgM has one extra CH4 domain

Question 11

Conformational determinant

Answer 11

Only recognizes folded, non-denatured proteins

Question 12

Linear determinant

Answer 12

If there is an accessible linear sequence, Ig can bind determinant in native form. If not, it must be denatured

Question 13

Neoantigenic determinant

Answer 13

Proteolysis creates a site that can be bound

Question 14

Affinity of Abs formed in the primary response vs Memory response

Answer 14

Lower affinity in primary, higher in memory response

Question 15

When is affinity critical

Answer 15

If Ag is toxin or Virus and must be eliminated immediately at low titers

Question 16

Ab valence

Answer 16

Maximum number of antigenic determinants with which it can interact

Question 17

IgG valence

Answer 17

IgG has two Fab regions and can bind two molecules of Ag - valence is 2

Question 18

Avidity and what it is dependent upon

Answer 18

Gives a measure of the overall strength of an Ab-Ag complex

Dependent on affinity of Ab for epitope and valence of both Ab and Ag

Question 19

Immature and mature B cells contain what Ig

Answer 19

IgM on immature

IgM and IgD on mature

Question 20

Changes in Ig after activation of B cells

Answer 20

Low rate of Ig secretion at first
Heavy chain isotype switching, affinity maturation
Then becomes Ab secreting cell w/high rate of Ig secretion and reduced membrane Ig

Question 21

Affinity maturation occurs when and where

Answer 21

Only occurs after activation, which would only occur in secondary lymphoid organs

Question 22

Ig with secretory component

Answer 22

Only IgA

Question 23

IFN-y signal to B cell

Answer 23

Signals B cell to become plasma cell and secrete IgG for phagocytosis

Question 24

TGF-B signal to B cell

Answer 24

Signals B cell to become plasma cell and secrete IgA for mucosal defense

Question 25

IL-4 signal to B cell

Answer 25

Signals B cell to become plasma cell and secrete IgE

Question 26

IL-2, 4, 5 signal to B cell

Answer 26

Signals B cell to become plasma cell and secrete IgM, causing complement activation

Question 27

IgA found

Answer 27

Mucosal secretions

Question 28

IgM found

Answer 28

Mostly in plasma

Question 29

IgE found

Answer 29

Absorbed on surface of mast cells

Question 30

IgG found

Answer 30

Penetrates deeper into the tissue

Question 31

IgG structure/function

Answer 31

Provides bulk of immunity for blood-born pathogens | Two heavy y(gamma) chains and either two Kappa or Lambda light chains

Question 32

What results in different subclasses of IgG

Answer 32

Slightly different sequences in their H-chains

Question 33

IgG and babies

Answer 33

IgG is the only Ab to cross the placenta and provide passive humoral immunity to developing fetus This will last for a couple weeks after birth

Question 34

FcRn

Answer 34

Cell surface receptor for Fc region of IgG in placenta, allows passing into fetal circulation

Question 35

IgD function

Answer 35

Low quantities in circulation | It is an Ag receptor on B lymphocytes

Question 36

Naive B cells express

Answer 36

Both IgM and IgD, which are specific for the same Ag | If Ag binds, it is internalized and presented to helper T cells

Question 37

IgM function

Answer 37

First Ab produced by Ag activated B cell Plays critical role in defense before sufficient IgG has been synthesized Found primarily in blood stream High avidity, making IgM effective in the removal of the microbe

Question 38

IgM structure

Answer 38

Five four-chain units held together by disulfide bonds | J-chain initiates polymerization of subunits during secretion from plasma cell

Question 39

IgA function/synthesis

Answer 39

Major Ig found in external secretions Most synthesized by plasma cells in mammary/saliva glands in respiratory, GI, GU tracts Major defense mechanism against microbes at mucosal surfaces

Question 40

Secreted IgA structure

Answer 40

In addition to L and H chains, also contains secretory component (SC) and and J-chain

Question 41

Secretory component (SC) function

Answer 41

Part of the Ig receptor involved in the transepithelial transport of exocrine IgA and stabilizes IgA against degradation in GI tract

Question 42

IgE function

Answer 42

Very low serum levels | Significant role in enhancing acute inflammation and protein from infection by worms and allergies

Question 43

IgE interaction with mast cells

Answer 43

IgE binds to receptors on mast cell that recognize Fc portion of Ig When Ag is introduced to a mast cell with IgE, it triggers activation and release of mediators