AQA AS Biology

Revision Notes

2.5.7 The B lymphocyte Response

The B lymphocyte Response

B-lymphocytes and the humoral immune response

  • B-lymphocytes (B cells) remain in the bone marrow until they are mature and then spread through the body, concentrating in lymph nodes and the spleen
  • Millions of types of B-lymphocyte cells are produced within us because as they mature the genes coding for antibodies are changed to code for different antibodies
  • Once mature, each type of B-lymphocyte cell can make one type of antibody molecule
  • At this stage, the antibody molecules do not leave the B-lymphocyte cell but remain in the cell surface membrane
  • Part of each antibody molecule forms a glycoprotein receptor that can combine specifically with one type of antigen
  • If that antigen enters the body, B-lymphocyte cells with the correct cell surface receptors will be able to recognise it and bind to it (clonal selection)
  • These specific B-lymphocytes divide repeatedly by mitosis (clonal expansion) and differentiate into two main types of cell:
    • Plasma cells
    • Memory cells
  • These two cell types each have a specific function

The maturation of B lymphocytes, downloadable AS & A Level Biology revision notes

The maturation of B-lymphocytes – by the time a child is born, it will have millions of different types of B-lymphocytes, each with a specific antibody receptor

Primary immune response

  • When an antigen enters the body for the first time, the small numbers of B-lymphocytes with receptors complementary to that antigen are stimulated to divide by mitosis
    • This is known as clonal selection
  • As these clones divide repeatedly by mitosis (the clonal expansion stage) the result is large numbers of identical B-lymphocytes being produced over a few weeks
  • Some of these B-lymphocytes become plasma cells that 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

Author:

Alistair graduated from Oxford University in 2014 with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems and Societies.
Close

Join Save My Exams

Download all our Revision Notes as PDFs

Try a Free Sample of our revision notes as a printable PDF.

Join Now
Already a member?
Go to Top