Lecture 10- Antibody classes and T-cell mediated immunity

Question 1

What are the two light chain types?

Answer 1

Kappa and lambda

Question 2

What are the five heavy chain types?

Answer 2

Mu, gamma, alpha, delta, and epsilon

Question 3

What are the classes of antibodies derived from heavy chain?

Answer 3

1. IgM
2. IgG
3. IgA
4. IgD
5. IgE

Question 4

Where is the difference between the light chains?

Answer 4

Their constant regions

Question 5

Where is the difference between heavy chains?

Answer 5

Their CH1, CH2, and CH3 regions

Question 6

What does each antibody consist of?

Answer 6

2 light chains and two heavy chains. For example an antibody has 2 kappa light chains and 2 Mu heavy chains or 2 lambda light chains and 2 gamma heavy chains etc

Question 7

List the features of the IgM antibody type?

Answer 7

1. Largest antibody class-pentamer
2. 10% of the antibody pool in the body
3. Mostly confined to the bloodstream and lymphatics
4. First antibody in the primary antibody response
5. Very effective at agglutination and complement activation.
6. Important defence against blood-borne spread of bacteria

Question 8

List the features of the IgG antibody?

Answer 8

> Small monomer

1. About 70-75% of the total immunoglobulin pool.
2. Diffuses rapidly into extravascular spaces
3. Only antibody class that can cross maternal-fetal placenta-important part in fetal immunity
4. Complement activation
5. Potent antitoxin antibody
6. Strongly bound by phagocytic cells
7. Enhancement of phagocytosis-opsonisation
8. Effective barrier against virus infections.

Question 9

List the features of IgA antibody?

Answer 9

1. 15-20% of human blood antibodies
2. Predominant class in sero-mucuc secretions
3. Protection of external body surfaces.
4. Prevents potential harmful material getting into the body through gut, respiratory tract and genitourinary tract.

Question 10

List the features of the IgD antibody?

Answer 10

1. Only present in trace amounts in blood and other body fluids.
2. Found on the surface of naive B-cells
3. Functions as a triggering receptor
4. Delivers activation signal to naive B cells through antigen binding.

Question 11

List the features of IgE antibody?

Answer 11

1. Found in trace amounts in the blood
2. During allergies and parasitic infections
3. Binds strongly to a class of basophils clled mast cells
4. When allergens bind to basophil associated IGE, processes are activated that lead to symptoms of allergy or asthma.

Question 12

What is the difference between humoral and cell-mediated immunity?

Answer 12

1. Humoral immunity is a product of B cells whereas cell mediated immunity is a product of T cells.
2. Humoral immunity involves antibodies and cell mediated immunity involves no antibodies.
3. Humoral immunity is effective against antigens outside cells and cell-mediated immunity is effective against intracellular antigens.
4. Humoral immunity used to fight viruses and cell-mediated immunity used to fight virus-infected cells.
5. Humoral immunity against toxins and cell mediated immunity against tumour cells.
6. Humoral immunity against extracellular bacteria and cell-mediated immunity for transplanted organs.

Question 13

What are the MHC(major histocompatibility complex) genes responsible for?

Answer 13

These genes code for the structures on the surface of cells which present antigens to T lymphocytes and are also recognised in the graft rejection.

Question 14

What do the MHC genes code for?

Answer 14

Class I and class II molecules via class I and class II loci

Question 15

What are the class I genes called and what do they code for?

Answer 15

Class I genes are called HLA-B, HLA-C and HLA-A and they code for the polypeptide chain that contains B-2 microglobulin.

Question 16

What are the class II HLA genes called and what do they code for?

Answer 16

Class II genes are called HLA-DP, HLA-DQ and HLA-DR and they code for the different transmembrane molecules.

Question 17

What are the different features of Class I and class II molecules?

Answer 17

Class I are found on all nucleated cells and class II are found on B cells and antigen presenting cells.
Both class I and class II are co-dominant and polymorphic( ie have many different alleles within population) 
Class I present peptides to CD8 T cells whereas class II present peptides to CD4 T cells.

Question 18

What do class I molecules show?

Answer 18

Class I show what’s going on inside the body. They present peptides that are naturally synthesised inside the cell for its normal function- this shows that the cell is functioning normally. If a virus infection occurs inside the cell, then the virus particles are broken down and one of them is presented. This indicates if there is an infection occuring in the cell.

Question 19

How are class Ii molecules different to class I?

Answer 19

Class I present peptides that are in the cell whereas class II show what has been taken up inside the cell from outside. Class II present those peptides to T cells, that are taken up inside the antigen presenting cells through phagocytosis/pinocytosis.

Question 20

All T cells have CD3 and TCR(t cell receptor), but what distinguishes cytotoxic T cells from helper T cells?

Answer 20

Cytotoxic T cells contain CD8 whereas helper T cells contain CD4.

Question 21

How does antigen presentation to T cells occur?

Answer 21

All T cells express receptors for antigen(celled T cell receptor) which recognise antigenic peptide fragments presented to them by MHC structures.
In addition, cytotoxic T cells have CD8 on the surface which recognises class I MHC peptides on the target cell(virus infected).
And helper T cells have CD4 on the surface which recognises class II MHC peptides on antigen presenting cells.

Question 22

What leads to the activation of cytotoxic T cells?

Answer 22

> Each T cell is associated with a particular antigen (And the cytotoxic T cells bind to class I molecules on virus infected cell). So the T cell receptor specific to that antigen will only bind and only the cytotoxic T cell will bind this MHC class I molecule.
After antigen specific binding, the helper signals are generated and these signal to the T cell if the bound antigen is dangerous.
If the helper cells recognise the peptide as dangerous, then the T cells will begin to divide(proliferate and differentiate)
T cells divide into two progeny
: 1st progeny= killer or cytotoxic T cells. These cells leave the lymphoid organ and move around the body to bind to the same peptide, that is bound to the MHC class I which interacted with the precursor T cell. Then the cytotoxic T-cell will bind to this peptide on each of the infected cells.(ie to the class I molecule on the infected cell) and destroy that cell.
:2nd progeny = Memory cells. These cells have the same T cell properties as the precursor T cell and bind the same antigen. These memory cells have a stronger secondary response against the antigen than the precursor T cell, so the destruction will be faster and more efficient if the body is exposed to this antigen again.