10- Immunology VII, VIII, IX

Question 1

When does induction of a precursor cell occur?

Answer 1

When antigen interacted with precursors antibody like receptor
This interaction leads to multiplication of precursor cell and differentiation or it’s descendants into antibody producing cells
Figure on page32

Question 2

What is immunogenic and non immunogenic?

What is hapten and hapten-carrier conjugate?

Answer 2

Immunogenic- substance that can induce antibody
Non-immunogenic- substance that cannot induce antibody
Small foreign molecules that are non-immunogenic are known as hapten
Hapten conjugated to immunogenic macromolecule is a hapten-carrier conjugate

Question 3

What are the two pieces of evidence against the direct antigen binding model? (Against the model on page 32)

Answer 3

1. Macromolecular haptens exist- appears that mere binding of antigen to antibody-like receptors (on precursor cell) would not result in induction if this antibody
2. Requirement for two cell types to obtain an antibody response- mouse given thymocytes and bone marrow cells separately with an antigen gave no response but when put together they triggered a response (page 34)

Question 4

What are helper or inducer T cells?

Answer 4

Cells From an area that are needed to allow antigen to induce another areas precursor cells to trigger a response
Bone marrow needs presence of thymocytes to allow precursor cells to produce progeny that secrete antibody

Question 5

Why do B cells require helper T cells to be activated by antigen?

Answer 5

A B cell can be induced by antigen if a second cell, the helper/inducer T cell, also binds to the antigen
Helper T cells only exist for foreign antigens, not self antigens
“Antigen-bridge model”
Page 35

Question 6

What was the antigen bridge model (page 35) modified?

What is the new model called?

Answer 6

It was found the helper CD4+ T cells do not bind intact antigen itself but a peptide derived from the antigen that is bound to an MHC class II molecule
Conjugate fuses into B cell via endocytosis then T cell bonds to MHC molecule
Me model is called MHC-restricted B cell/T helper cell interaction model page 36

Question 7

What is the mechanism ensuring that precursor cells specific for self-antigens are induced?

Answer 7

The property of self antigens that distinguishes them from foreign antigens is their early and continuous presence, and the immune system utilizes this property in avoiding self reactivity
Page 37 picture
This explains why foreign antigens that arise during development are seen as self antigens

Question 8

Can a self antigen interact with the receptors of B cells in the absences of T cells? If so what happens? (What’s the process called)

Answer 8

When self antigens interact with B cells it results in the death of the B cell
This results in anti-self B cells to be eliminated
Process is called antigen specific inactivation

Question 9

What is crossreactivity and epitopes?

Answer 9

Epitopes are areas of antigen molecule complementary to an antibody
Some antigens have very similar or identical epitopes which means stuff like mouse and rat serum can crossreact when antibodies against the serum are added from eachother to eachother

Question 10

How can crossreactivity lead to autoimmunity?

Example with heart and streptococci?

Answer 10

Immunization with antigens that crossreact with self antigen sometimes cause autoimmunity directed against the self antigen
Example of Hashimotos autoimmune disease on page 39-40
Also group A streptococci bacteria cross react with heart tissue and can develop rheumatic heart disease due to autoimmune response to heart tissue