AQA A Level Biology复习笔记2.5.10 Plasma & Memory Cells

• During an immune response, B-lymphocytes form two types of cell: plasma cells and memory cells
• Memory cells form the basis of immunological memory – the cells can last for many years and often a lifetime
• There are two types of immune response:
  • Primary immune response (responding to a newly encountered antigen)
  • Secondary immune response (responding to a previously encountered antigen)

   

Primary immune response

• After clonal selection and expansion, the B-lymphocytes that have become plasma cells  secrete lots of antibody molecules (specific to the antigen) into the blood, lymph or linings of the lungs and the gut
• These plasma cells are short-lived (their numbers drop off after several weeks) but the antibodies they have secreted stay in the blood for a longer time
• The other B-lymphocytes become memory cells that remain circulating in the blood for a long time
• This response to a newly encountered pathogen is relatively slow

Secondary immune response

• If the same antigen is found in the body a second time, the memory cells recognise the antigen, divide very quickly and differentiate into plasma cells (to produce antibodies) and more memory cells
• 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
• This response to a previously encountered pathogen is, relative to the primary immune response, extremely fast

During a secondary immune response, memory cells that remained in the blood divide very quickly into plasma cells (to produce antibodies) and more memory cells