Adaptive immunity and antibody structure

Question 1

What is adaptive immunity

Answer 1

Specific immunity
Develops after a pathogen has been encountered before
Is more efficient the second time round

Question 2

What are the organs responsible for adaptive immunity

Answer 2

Lymphoid system eg spleen, thymus, bone marrow, lymph nodes etc

Question 3

What are the lymphocytes involved in adaptive immunity and what do they recognise

Answer 3

B and T lymphocytes B-differentiate bone marrow
T- differentiate in thymus

They recognise SPECIFIC molecule on pathogen- ANTIGEN
Therefore B and T are immunocompotent cells

Question 4

What is adaptive immunity split into

Answer 4

cell mediated (T) and humoral (B) and T cells

Humoral mediated by antibodies

Question 5

Difference between membrane bound and soluble antibodies

Answer 5

Initially , the virgin B cell has membrane bound antibodies (not souble)

But after antogen stimulation and B cells differentiate to plasma cells, they secrete SOLUBLE antibodies
(loses their transmemebrane domain)

ADAPTIVE HUMORAL IMMUNITY IS DONE BY SOLUBLE ANTOBODIES

Question 6

Structure of antibodies

Answer 6

Quarternary structure- 4 polypeptide chains, 2 light, 2 heavy chains. Held together by disulfide bonds

Has hinge region where it bends

Has 2 antigen binding sites (variable region)

Question 7

Difference between the lower part of the antibody in soluble and membrane bound

Answer 7

Soluble: bottom hydrophillic

Memebrane: longer bottom half and has hydrophobic domain to anchor heavy chain to the membrane of b cell.

Question 8

What 2 other proteins bind next to membrane bound antibodies
What is this complex

Answer 8

Iga and IgB= forms the functional b cell receptor complex

Involved in signal transduction- when antobody binds to the antigen, they activate protein kinases so signal gets to b cell

Question 9

What post translational modifcation does an immunoglobin have

Answer 9

It is glycosylated

Question 10

How many domains do each chain have

Answer 10

Light= 1 variable and 1 constant
Heavy= 4 or 5 domains, 1 variable the rest contant

variable heavy and varibale light make up the antigen binding sites

Question 11

For each variable domain (1 heavy and 1 light) what is the region they have

Answer 11

3 looped shaped hypervaribale regions

The 3 hypervariable regions on heavy come close to 3 hypervaribale regions on light to form ANTIGEN BINDING SITE.
= CDR (complementarity determining regions)

These 6 CDRs hold the antigen when antibody binds

Question 12

What are the varibale domain regions other than CDRs

Answer 12

Framework regions

Forms beta sheet keeping CDRs in position

Question 13

Is the contstant part of the antibody always the same

Answer 13

No, they can be different as genotype encodes for different ISOTYPES

Question 14

What are the isotypes of light chain and heavy chain

Answer 14

Light- 2: kappa and lamda, similar and perform same functions

Heavy- 5: γ (IgG) , α (IgA), μ (IgM), δ (IgD) and ε (IgE)
Differ in structure and function.

Question 15

Which of the 5 isotypes for heavy chains has an extra 5th domain instead of 4

Answer 15

IgM and IgE

Question 16

Normally, memebrane bound antibodies and some soluble antibodies are monomers as in the basic y 4 chain structure.

Which solube antobodies are not monomers

Answer 16

IgA is a dimer ( 2 y bound together by J chain)

IgM is a pentamer ( 5 y bound by J chain and dilsulfide bonds)

Question 17

Blood serum has albumins and globulins

Which globulin is immunoglobulins made of

Answer 17

Gamma globulins

Question 18

How is the immunoglobulin structure studied

Answer 18

1. put in reducing conditions
2. Difsulfide binds broken, antibody split into light and heavy chain
3. Protease PAPAIN cleaves antibody into 3 fragments
4. 2 of them identical - FAB fragments (fragment antigen binding).
5. 3rd fragemnt is called FC (fragment crystallizable)

Question 19

So where does papain cut the antibody

Answer 19

Hinge region

Question 20

Why are antibodies of different individuals against the same antigen different

Answer 20

Because they are polyclonal antobodies- made by dofferent B lymphocytes

Question 21

What are monoclonal antobodies

Answer 21

Antobodies produced by identical B cells
As in clonal expnasion from 1 single b cell

Question 22

Production of monoclonal antibodies

Answer 22

1. mouse injected with antigen from which we want the specific antobodies - triggers immune response
2. B cells taken from mouse and mixed with myeloma cells
3. This makes HYBRIDOMA CELLS - prodce 1 type of antobody

Monoclonal can be used for reasearch (immunocytochemistry), diagnostic tests, cancer treatment

Question 23

Is the antigen antibody complex a chemical reaction

Answer 23

No it is not
Bc covalent bonds are not rearranged or broken, requires no enxyme either so is reversible

The complex has non covalent ineractions like ioic hydrogen van der waals

Question 24

What are paratopes and epitopes

Answer 24

Paratope on the antogen binding site of antibody binds to the epitope which is in the antigen - lock and key fit

Question 25

How many epitopes does an antigen have

Answer 25

Many, some identical some dfferent

Question 26

How is the strength of binding measured by

Answer 26

affinity of antibody

Antibodies with affinity to only one epitope
are called specific.
Some antibodies can react with 2 or more epitopes.
They are called cross-reactive.

IgG high affinity

Question 27

What are the 2 properties of antigens

Answer 27

Antigenicity=is the ability to react with an already synthesized
antibody

Immunogenicity=is the ability to trigger the synthesis of
a specific antibody

Question 28

Can lymphocytes recognise if the antgen is self or foregn

Answer 28

no

needs other mchanisms to do so

EACH person has their ownj HLA? (human lymphocyte antigen)

Question 29

To be immunogenic what does a molecule (antigen) have to be

Answer 29

(1) large and (2) a polysaccharide, a protein, or a derivative
of either.

Question 30

So why does antibodies have a bias towards protein antigens

Answer 30

Because of t helper cells trying to trigger humoral respinse

Question 31

What are the 2 epitopes of antigens (protein)

Answer 31

linear and conformational

Question 32

difference between linear and conformational

Answer 32

A linear epitope includes several adjacent amino acids. Antibodies against such
epitopes react with both native and denatured antigen.

A conformational epitope includes amino acids at distant positions in the
polypeptide chain, brought together in the tertiary structure. Antibodies against
conformational epitopes react only with the native antigen.

Question 33

What is a hapten

Answer 33

A hapten is a small molecule which is antigenic but not
immunogenic. We can imagine it to be a single epitope cut off from a larger antigen molecule