The Immune System

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Slide 13

B -Lymphocytes

At the clone stage antibodies do not leave the B-cells.

The abs are embedded in the plasma membrane of the cell and are

called antibody receptors.

When the receptors in the membrane recognise and antigen on the surface of the pathogen the B-cell divides rapidly.

The antigens are presented to the B-cells by macrophages

Slide 14

B -Lymphocytes

Slide 15

B -Lymphocytes

Some activated B cells  PLASMA CELLS these produce lots of antibodies, < 1000/sec

The antibodies travel to the blood, lymph, lining of gut and lungs.

The number of plasma cells goes down after a few weeks

Antibodies stay in the blood longer but eventually their numbers go down too.

Slide 16

B -Lymphocytes

Some activated B cells  MEMORY CELLS.

Memory cells divide rapidly as soon as the antigen is reintroduced.

There are many more memory cells than there were clone cells.

When the pathogen/infection infects again it is destroyed before any symptoms show.

Slide 17

Slide 18

Antibodies

Also known as immunoglobulins

Globular glycoproteins

The heavy and light chains are polypeptides

The chains are held together by disulphide bridges

Each ab has 2 identical ag binding sites – variable regions.

The order of amino acids in the variable region determines the shape of the binding site

Slide 19

How Abs work

Some act as labels to identify

antigens for phagocytes

Some work as antitoxins i.e. they block toxins for e.g. those causing diphtheria and tetanus

Some attach to bacterial flagella making them less active and easier for phagocytes to engulf

Some cause agglutination (clumping together) of bacteria making them less likely to spread

Slide 20

Different Immunoglobulins

Slide 21

Slide 22

T-Lymphocytes

Mature T-cells have T cell receptors which have a very similar structure to antibodies and are specific to 1 antigen.

They are activated when the receptor comes into contact with the Ag with another host cell (e.g. on a macrophage membrane or an invaded body cell)