B-cells and T-helper cells

By Jess and Christie

Third line of defence

Pre-testQuestions Answer Before Answer After

What do B cells do?

What do T cells do?

Immune system?? What’s an immune system??

According to Nature of Biology Book 2 3edition, the immune system is group of lymphoid tissues and organs and lymphatic vessels that assist the body to resist infection and disease through specialised cells such as macrophages, neutrophils, B cells and T cells

I've heard there are 3 lines of defence. What are they??

The 1st line of defence is the skin, mucus's and natural successions.

The 2nd line of defence is white blood cells

The 3rd line of defence is the B and T cells

B-cells and T-cells....they sound interesting. What are they???

B lymphocytes ( B cells) and T lymphocytes (T cells) are The most abundant types lymphocytes

Lymphocytes are one of the 5 kinds of white blood cells circulating in the blood

B cellT cell

That’s cool…..Where are they formed???

• B cells are produced in the bone marrow. The precursors (Something that comes first/before) of the T cells are also produced in the bone marrow but leave the bone marrow and mature in the thymus.

So…what do they do in relation to the immune system??

Each B cell and T cell is specific for a particular antigen. This means that each is able to bind to a particular molecular structure. The specificity of binding resides in a receptor for antigen:

• The B cell receptor (BCR) for antigen.

• The T cell receptor (TCR) for respectively

Both BCRs and TCRs share these properties:• Both integral membrane proteins.• Are present in thousands of identical copies exposed at the cell surface.• Are made before the cell ever encounters an antigen.• They are encoded by genes assembled by the recombination of segments

of DNA.• Have a unique binding site.• This site binds to a portion of the antigen called an antigenic determinant

or epitope.• The binding like that between an enzyme and its substrate depends on the

complementarity of the surface of the receptor and the surface of the epitope.

• The binding occurs by non- covalent forces (Like an enzyme binding to its substrate).

BCRs and TCRs differ in:• Their structure.• The genes which encode them.• The type of epitope to which they bind.

B cells- • -BCRs bind soluble antigens ( like

diphtheria toxoid, the protein introduced into your body in the DTP vaccine).

• -Helper T cell specific for this structure bind the B cells.

Lymphokines:• Stimulate the B cells to enter the cell

cycle and develop, by repeated mitosis, into a clone of cells with identical BCRs.

• Switch from synthesizing their BRCs as integral membrane proteins to a soluble version.

• Differentiate into plasma cells that secrete these soluble BCRs, which we now call antibodies.

T cells-

• The surface of each T cell also displays thousands of identical t cell receptors (TCRs)

• There are two types of T cells that differ in their TCR:

• Alpha/ beta T cells. There TCR is a heterodimer of an alpha chain with a beta chain, has a variable (V) region and a constant (C ) region. Each V regions each contain 3 hyper variable regions that make up the antigen binding site.

• Gamma/ Delta T cells. Their TCR is also a heterodimer of a gamma chain paired with a delta chain.

I think I get it....but…..

• Here maybe this video will help

• http://www.youtube.com/watch?v=90hSVkaOG_w&feature=BFa&list=PL9EE3469FAE60F5F9

So to the T and B cells attack anything??

Well no...The first and second lines of defence are ‘non-

specific’ and attack anything that is ‘non- self’....The third line of defence, B cells and T cells are

‘specific’ and only attack certain things that are non-self

Hang on, you said ‘non-self’…. What's that???

‘non-self ’ is any cell or agent that is foreign to the body and is therefore tagged as ‘non-self’ and is targeted by the immune systemAnything tagged as ‘self’ shouldn't be attacked by the

immune system (except in rare cases)

Well I’v learnt a lot today. HAVE YOU???

Questions Before Answer After Answer

What do B cells do?

What do T cells do?