Memory Cells & Immunity (Cambridge (CIE) A Level Biology): Revision Note

Memory cells & long-term immunity

Developing immunity

• The immune system is activated when a new antigen is encountered

• This launches a primary immune response consisting of:

  • A non-specific immune response

  • Followed by a specific immune response

• The primary response occurs the first time an antigen is encountered by the immune system

  • Since it is the first time the immune system has encountered the antigen, the numbers of T and B cells with the correct membrane receptors present in the blood will be low

• It will take time for the correct lymphocytes to be activated and to divide and for different cell types to develop

  • It can take several days before plasma cells develop and are able to start producing antibodies against an antigen

  • This is the reason why an infected person will experience symptoms of the disease the first time they contract it

• The primary response produces memory cells which remain in the blood after an infection is over

  • The presence of memory cells means that a person is said to be immune to the pathogen

  • Memory cells can remain in the blood for many years, so the immunity gained from a primary response can be long-term

• Should the immune system encounter the same antigen again in the future it will launch a secondary immune response which will be much faster and stronger than the primary response

  • Memory cells are present in larger quantities than the mature lymphocytes at the start of the primary response

    • This means the correct memory cells are able to detect an antigen, activate and divide by mitosis much more quickly

  • Antibodies are produced more quickly and in larger concentrations in a secondary response

• This will often eliminate the pathogen before the infected person can show symptoms