1. Cell Signalling and communication between cells.

2. Key definition: Cell signalling is the communication between cells that allows effective coordination of a response.

3. Cell signalling in the immune system. Cell signalling is vital in the immune system, it helps to activate all the different types of white blood cells that are needed. Communication is achieved through cell surface molecules, and through the release of hormone- like chemicals called ‘cytokines’. To be able to detect these molecules the cell must have a surface receptor, the surface receptor must be specific, this is to ensure that they only bind and respond to that specific molecule.

4. Cytokines are chemical signals that act as instructions to their target cells, there are a range of cytokines that can be released. They bind to the specific receptors on the target cell, which then alters the behaviour of the target cell.

5. Pathogens carry an antigen on its cell surface, they act as markers, they enable it to be detected by our body cells, as a ‘foreign cell’. Our own cells also carry antigens, but they are recognised as ‘self’. In order to avoid destroying any ‘self’ cells, the immune system will contain no cells with complimentary receptors for our own antigens, this means no ‘self’ cells can stimulate an immune response.

6. A foreign antigen will stimulate a response, the response results in the production of ‘antibodies’ from the B-lymphocytes. The immune system needs to manufacture an antibody for each antigen recognised by the immune system, so the antibodies can attach to the antigen causing them to become harmless.