Plasma & Memory Cells (AQA A Level Biology) : Revision Note
Plasma & Memory Cells
During an immune response B-lymphocytes give rise to:
plasma cells, which produce antibodies
memory cells, which form the basis of immunological memory
Plasma cells and memory cells are involved in two different levels of immune response:
primary immune response to a newly encountered antigen
secondary immune response to a previously encountered antigen
Primary immune response
After clonal selection and mitosis the B-lymphocytes that have become plasma cells secrete specific antibodies into the blood
These plasma cells are short-lived and antibody numbers gradually decrease over time after the response has ended
Some B-lymphocytes develop into memory cells that remain in the blood for a long time
The primary response to a newly encountered pathogen is relatively slow, due to:
time taken to find lymphocytes with complementary receptors (clonal selection)
time taken for mitosis to occur
time taken for antibody production to begin
Secondary immune response
If the same antigen is encountered a second time the memory cells recognise the antigen, divide very quickly and differentiate into plasma cells to produce antibodies
This response is very quick, meaning that the infection can be destroyed and removed before the pathogen population increases too much and symptoms of the disease develop


Examiner Tips and Tricks
Immunological memory is the reason why catching some diseases twice is so unlikely. Some infections however, such as the common cold and influenza, are caused by viruses that constantly mutate and that show antigenic variability. As each strain has different antigens the primary immune response must be carried out each time before immunity can be achieved.
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