immunoglobulins

Question 1

what is another name for immunoglobulins

Answer 1

antibodies

Question 2

what do antibodies do

Answer 2

they recognise antigens

Question 3

what is an antigen

Answer 3

any substance which elicits an immune response

Question 4

portion recognised =?

Answer 4

epitope or antigenic determinant

Question 5

where are antibodies present

Answer 5

plasma, tissues, secretions and lymphatic system

Question 6

what are the 5 classes of immunoglobulins

Answer 6

IgG
IgM
IgA
IgD
IgE

they provide recognition function and trigger effector functions

Question 7

what bond holds immunoglobulins together

Answer 7

disulphide bridges

Question 8

what is Fab

Answer 8

Fragment antigen binding - responsible for binding antigen

Question 9

what is Fc

Answer 9

Fragment crystallisable - responsible for effector function

Question 10

what are the two types of light chains

Answer 10

Lamba and kappa
all antibody classes use these same light chains

in any individual antibody molecule both light chains are the same

Question 11

what determines the class of antibodies

Answer 11

heavy chains

Question 12

light chains fold up into how many globular domains

Answer 12

2

Question 13

heavy chains fold up into how many globular domains

Answer 13

4 or 5

Question 14

what is each domain comprised of and what links them

Answer 14

they are comprised of 2 beta sheets and are linked by disulphide bridges to form a beta barrel

Question 15

what do n-linked oligosaccharides attach to

Answer 15

Asn residue in the sequence Asn-X-Ser/Thr where x is an amino acid except Pro

Question 16

what does CDR stand for

Answer 16

complementary determining region

Question 17

what happens when VH and VL domains are paired

Answer 17

their 6 CDRs lie close together and create the antigen-binding site

Question 18

what do antibodies recognize

Answer 18

structural epitope on the antigen

Question 19

antiboy binds antigens with various (blank) interactions

Answer 19

non-covalent

Question 20

Electrostatic forces

Answer 20

Attraction between opposite charges e.g.NH3+ and COO-

Question 21

Hydrogen bonds

Answer 21

Hydrogen shared between electronegative atoms (N, O)

Question 22

Van der Waals forces

Answer 22

Fluctuations in electron clouds around molecules oppositely polarise neighboring atoms

Question 23

Hydrophobic forces

Answer 23

Hydrophobic groups interact unfavourablywith water and tend to pack together toexclude water molecules. The attractionalso involves Van der Waals forces

Question 24

explain and describe IgG

Answer 24

1. Most abundant Ig in plasma (10 mg/ml)
2. Y shaped2 HC of 50 kDa mass, 2 LC of 25 kDa mass4 subclasses - IgG1, IgG2, IgG3, IgG4
3. Very efficient at triggering complement and phagocytosis via Fc receptors
4. Only Ig class to cross the placenta from mother to fetus - protects baby in first months of life
5. Predominant antibody of 2o response

Question 25

explain and describe IgM

Answer 25

1. Only in plasma and secretions - too large to enter tissues 2. Pentamer - 5 Y-shaped units joined by Joining (J) chain and disulfide bridgesHeavy chain has 5 globular domains 4. Very efficient at activating complement 3. Ten binding sites for antigen - very good agglutinating particles e.g. viruses 5. Predominant antibody of 1o response

Question 26

explain and describe IgA

Answer 26

Important serum Ig (2-3 mg/ml) Major antibodies in seromucous secretions.g. saliva, milk, colostrum gut, tracheobronchial system genito-urinary system Class of antibody first encountered by many invading bacteria and viruses 1. Two subclasses - IgA1, IgA2 2. Monomeric and dimeric forms 3. Serum IgA – monomeric90% IgA1, 10% IgA2 4. Secretory IgA - predominantly dimeric40% IgA1, 60% IgA2Additional polypeptide (secretory component SC)derived from receptor mediating export to secretions 5. SC protects in the harsh environments of secretions

Question 27

IgE function

Answer 27

Associated with an allergic response Important for protection against parasitic infections

Question 28

IgD

Answer 28

Very low serum concentrations Found on the surface of lymphocytes Function unclear - may be involved in the control of antibody response Recently implicated in mucosal immunity

Question 29

Neutralizing antibodies=

Answer 29

IgG and IgA are efficient at binding to soluble toxins preventing them from binding to cell surface receptors

Question 30

what do allergic individuals make

Answer 30

IgE responses to innocuous antigens (allergens)FcRI is cross-linked ---> release of inflammatory mediators like histamine

Question 31

summary

Answer 31

Structure on antigen recognised by an antibody is termed the‘epitope’ or ‘antigenic determinant’ Antibodies fold into globular domains with distinctive 3D structure Hypervariable regions (CDR) in variable domains govern antigenbinding Three-dimensional complementarity of structures of antigen binding site and antigen lead to high specificity and affinity Different Ig isotypes are expressed at different body sites and have different functions Antibodies act as flexible adaptors, linking antigen recognition to elimination mechanisms Key functions of antibodies are blocking, neutralization, complement activation and cell activation through Fc receptor