Structure And Function Of Immunoglobulins

Front 1

Plasma vs. Serum

Back 1

Plasma: cell free portion of blood containing clotting factors

Serum: is the liquid portion of blood without clotting factors etc. that is left after formation of a clot

Front 2

Polyclonal vs monoclonal serum

Back 2

Polyclonal serum contains various antibodies from many B-lymphocytes

Front 3

What is a multiple myeloma?

Back 3

A tumour of plasma B cells

Front 4

Why is a multiple myeloma beneficial to lab science?

Back 4

Considering it is a tumour effecting cells that secrete antibodies it provides a method to produce massive amounts of secreted antibodies

Front 5

What is a hybridoma?

Back 5

A process where cells are harvested from mouse spleen and crossed with mutant multiple myelomas. The mutation prevents the cells from growing in HAT medium although the fusion enables them to.

Therefore it produces this hybridoma that is capable of producing massive amounts of the antibody that the mouse was immunized for

Front 6

What are the five types of immunoglobulin?

Back 6

IgA, IgE, IgM, IgG and IgD

Front 7

Properties of each Ig molecule?

Back 7

Antigen binding

Effector function

Front 8

What is the structure of Ig?

Back 8

All Ig are composed of at least 1 heterodimer that consists of one heavy chain (two parts) and one light chain

Front 9

How are the dimers held together?

Back 9

By disulphide bonds in the bent region

Front 10

What is the Fc region

Back 10

It is the terminal end of the antibody consisting of two heavy chains that interacts with Fc receptors on the immune cells

Front 11

How are the effector functions of an antibody achieved?

Back 11

Generally occur when the Fc region binds to a receptor on an immune cell and causes biological effects

Front 12

Three ways that the effector functions can occur

Back 12

1. Neutralization: Antibody binds to free toxin in circulation and subsequently prevents it from binding to a receptor (will lead to its engulfment)

2. Opsonization: Bind antigens on a pathogen and interaction with the Fc receptor will lead to its internalization

3. Activation of complement: Binding of Ab to Ag will cause complement to bind the pathogen and lyse it

Front 13

Cell mediated antibody effector functions

Back 13

Antibody binding to surface antigen on target cell (could be our own cell if infected by virus) and in turn recruits NK cells with Fc receptors

Front 14

What is the response of NK cell binding to the Fc region of the antibody?

Back 14

The NK cell receptors will crosslink with the Fc region triggering the release of cytotoxic molecules culminating in apoptosis

Front 15

Where are disulphide bonds found in an immunoglobulin?

Back 15

Interchain: linking heavy chains or linking light and heavy chains

Intrachain: within either the heavy or light chain

Front 16

What are the domains of the heavy chain?

Back 16

C1,2, and 3 and V1

The top of the heavy chain that interacts with the antigen is variable and this is followed by the first constant region.

After the hinge region there are two more constant regions

Front 17

What are the domains of the light chain?

Back 17

The top portion is variable followed by a single constant region. The light chain doesn't extend past the hinge region.

Front 18

What is the role of the hinge region?

Back 18

Provides flexibility to the antibody to properly bind its antigen if its topology may be difficult to interact with

Front 19

Which antibodies don't have a hinge region?

Back 19

IgM and IgE

Front 20

What is a characteristic structural feature in the immunoglobulin family?

Back 20

The contain domains of antiparallel beta sheets

Front 21

What are hyper variable regions?

Back 21

Specific amino acid sequences in the variable region of either antibody heavy or light chains that have incredible variability, flanked by regions of less variability

Region that actually binds the Ab

Front 22

Papain and pepsin

Back 22

common proteases that are used to digest antibodies for the purpose of decoding their structure

Front 23

Papain site of action

Back 23

Papain acts on the hinge region of the antibody cleaving it into two FAB regions (fragment antibody binding) and the FC region

Front 24

Pepsin site of action

Back 24

Cleaves apart the FC region preserving the FAB region (the two parts stay attached)

Front 25

Which immunoglobulin classes have subclasses?

Back 25

IgG (gamma 1,2,3 and 4) and IgA (alpha 1 and 2)

Front 26

What are the two forms of the light chain and which is more prominent?

Back 26

Kappa and lambda (kappa is more prominent)

Front 27

Order of immunoglobulin content (greatest to least)

Back 27

IgG, IgA, IgM, IgD, IgE

Front 28

Effect of IgG binding to Fc receptors

Back 28

Activates complement and cell-mediated cytotoxicity

Front 29

How do IgG and complement work together?

Back 29

IgG binds the pathogen and brings it to the Fc receptor enabling the C3b complement to interact with its receptor CR1 (causes phagocytosis)

IgG basically activates the complement

Front 30

Structure of IgA in secretions

Back 30

Forms an immunoglobulin dimer where the individual immunoglobulins are connected by the J chain and a secretory component

Front 31

What is the secretory component

Back 31

It is derived from epithelial cells and helps to hold together the IgA dimer and disguise it from proteases found in these secretions

Front 32

Common secretions with IgA

Back 32

Tears, saliva, breast milk, GI tract etc.

Front 33

Explain how IgA enters into the gut lumen

Back 33

IgA binds to the pIgR (Poly-Ig receptor) on the surface of the epithelium and is transported by vesicle to the surface where it is cleaved from the receptor and can enter the lumen

Front 34

Main role of IgA

Back 34

To neutralize pathogens and prevent their attachment to epithelial cells

Front 35

True or false, IgA activates the complement pathway

Back 35

False, IgA is not capable of activating the complement pathway

Front 36

Unique structure of IgM

Back 36

Is a pentamer in serum where the five immunoglobulin units are connected by disulphide bridges and a j chain

Front 37

What is the structure of IgM when bound to a B cell

Back 37

It is a monomer

Front 38

First antibody to appear in phylogeny

Back 38

IgM

Front 39

Antibodies that do not cross the placenta

Back 39

IgA and IgM

Front 40

Best Ab at activating complement pathway

Back 40

IgG

Front 41

Lacks a hinge region

Back 41

IgM does although it remains relatively flexible

Front 42

This Ab is largely confined to the B cell membrane

Back 42

IgD

Front 43

Ab responsible for binding mast cells and basophils (what is the role of this)

Back 43

IgE plays a major role in allergy response and potential for anaphylaxis

Causes degranulation of mast cells

Front 44

Antigenic determinant

Back 44

A portion of the antigen binding region that acts as an epitope and can be bound by other antibodies