AS AQA Biology - The Immune System

Antigen: molecule found on a cells surface

Phagocyte: type of white blood cell that carries out phagocytosis

T-cell: type of white blood cell

B-cell: type of white blood cell

Plasma cell: clone of the B-cell

Cytokine: enzyme that makes cells divide

Lysis: rupturing the cell

The pathogen recognises foreign antigens on the pathogen, this activates the immune response

The phagocytes cytoplasm engulfs the pathogen into a phagocytic vacuole/phagosome

A lysosome attaches itself to the phagosome and releases lysosomal enzymes to break down the pathogen

When the pathogen has been broken down, the phagocyte presents the foreign antigens on its surface to activate the next stage of the immune response.

When antigens have been presented by the phagocyte, T-cells are activated

T-cells have proteins on their surface which binds to the foreign antigens

There are two ways in which a T-cell could respond:

• They could release substances to activate the B-cells

or

• They could attach to a pathogen via the antigens, and kill it by the process of lysis

If the substances are released, B-cells are activated

B-cells are covered with antibodies, and the antibodies bind to a complementary antigen to form an antigen-antibody complex

The B-cell then divides into plasma cells via cytokines.

Plasma cells secrete antibodies that are specific to the foreign antigen

The functions of these antibodies are:

• Coating the pathogen to stop it from entering host cells
• Coating the pathogen to make it easier to engulf
• Binding to the toxins that the pathogen released and neutralising them

Some features of antibodies include:

• They're proteins - made of chains of amino acids linked by peptide bonds
• They're specific - each antibody has a different shaped variable region (see next slide) that is complementary to one specific antigen
• The constant regions (see next slide) are the same in all antibodies

Here is a diagram of an antibody: