The B Lymphocyte Response (OCR A Level Biology): Revision Note

Specific Immune Response: B Lymphocytes

Maturation of B-lymphocytes

• 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

• During the process of maturation B cells gain specific cell surface receptors called B cell receptors (BCRs)

  • The receptors on the cell surface of B cells are antibodies and are sometimes referred to as antibody receptors

  • Part of each antibody molecule forms a glycoprotein receptor that can combine specifically with one type of antigen

  • A small number of B cells have the same BCRs, these genetically identical cells are called a clone

Mature B cells have many different types of antibody receptor on their cell surface membranes

B cells in the immune response

• In order to play their role in the immune response B cells need to be activated and increase in number; this occurs as follows:

• Clonal selection and activation

  • B cells with complementary antibody receptors bind to antigens on antigen presenting cells; this is clonal selection

    • These antigen presenting cells can be phagocytes, infected cells, or the pathogens themselves

  • This binding, together with interleukins released by T helper cells activates the B cells

• Clonal expansion

  • Activated B cells divide by mitosis to produce clones

  • This results in large numbers of identical B-lymphocytes being produced over a few weeks

  • Some of these B-lymphocytes differentiate into plasma cells

    • Plasma cells secrete lots of antibody molecules (specific to the antigen) into the blood, lymph or linings of the lungs and the gut

  • The other B-lymphocytes become memory cells that remain circulating in the blood for a long time

Activated B cells differentiate into plasma cells and memory cells