Adaptive immunity and antibody structure Flashcards
What is adaptive immunity
Specific immunity
Develops after a pathogen has been encountered before
Is more efficient the second time round
What are the organs responsible for adaptive immunity
Lymphoid system eg spleen, thymus, bone marrow, lymph nodes etc
What are the lymphocytes involved in adaptive immunity and what do they recognise
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
What is adaptive immunity split into
cell mediated (T) and humoral (B) and T cells
Humoral mediated by antibodies
Difference between membrane bound and soluble antibodies
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
Structure of antibodies
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)
Difference between the lower part of the antibody in soluble and membrane bound
Soluble: bottom hydrophillic
Memebrane: longer bottom half and has hydrophobic domain to anchor heavy chain to the membrane of b cell.
What 2 other proteins bind next to membrane bound antibodies
What is this complex
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
What post translational modifcation does an immunoglobin have
It is glycosylated
How many domains do each chain have
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
For each variable domain (1 heavy and 1 light) what is the region they have
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
What are the varibale domain regions other than CDRs
Framework regions
Forms beta sheet keeping CDRs in position
Is the contstant part of the antibody always the same
No, they can be different as genotype encodes for different ISOTYPES
What are the isotypes of light chain and heavy chain
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.
Which of the 5 isotypes for heavy chains has an extra 5th domain instead of 4
IgM and IgE
Normally, memebrane bound antibodies and some soluble antibodies are monomers as in the basic y 4 chain structure.
Which solube antobodies are not monomers
IgA is a dimer ( 2 y bound together by J chain)
IgM is a pentamer ( 5 y bound by J chain and dilsulfide bonds)
Blood serum has albumins and globulins
Which globulin is immunoglobulins made of
Gamma globulins
How is the immunoglobulin structure studied
- put in reducing conditions
- Difsulfide binds broken, antibody split into light and heavy chain
- Protease PAPAIN cleaves antibody into 3 fragments
- 2 of them identical - FAB fragments (fragment antigen binding).
- 3rd fragemnt is called FC (fragment crystallizable)
So where does papain cut the antibody
Hinge region
Why are antibodies of different individuals against the same antigen different
Because they are polyclonal antobodies- made by dofferent B lymphocytes
What are monoclonal antobodies
Antobodies produced by identical B cells
As in clonal expnasion from 1 single b cell
Production of monoclonal antibodies
- mouse injected with antigen from which we want the specific antobodies - triggers immune response
- B cells taken from mouse and mixed with myeloma cells
- This makes HYBRIDOMA CELLS - prodce 1 type of antobody
Monoclonal can be used for reasearch (immunocytochemistry), diagnostic tests, cancer treatment
Is the antigen antibody complex a chemical reaction
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
What are paratopes and epitopes
Paratope on the antogen binding site of antibody binds to the epitope which is in the antigen - lock and key fit
How many epitopes does an antigen have
Many, some identical some dfferent
How is the strength of binding measured by
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
What are the 2 properties of antigens
Antigenicity=is the ability to react with an already synthesized
antibody
Immunogenicity=is the ability to trigger the synthesis of
a specific antibody
Can lymphocytes recognise if the antgen is self or foregn
no
needs other mchanisms to do so
EACH person has their ownj HLA? (human lymphocyte antigen)
To be immunogenic what does a molecule (antigen) have to be
(1) large and (2) a polysaccharide, a protein, or a derivative
of either.
So why does antibodies have a bias towards protein antigens
Because of t helper cells trying to trigger humoral respinse
What are the 2 epitopes of antigens (protein)
linear and conformational
difference between linear and conformational
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.
What is a hapten
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
