The B lymphocyte Response (AQA AS Biology): Revision Note

The B lymphocyte (humoral) response

• Each mature B lymphocyte has a specific antibody on its surface, which acts as a receptor

• Clonal selection occurs when a B cell binds to a complementary antigen

• The activated B cell divides by mitosis (clonal expansion) into:

  • plasma cells – secrete large amounts of antibodies

  • memory cells – remain in circulation and provide a faster secondary response

• The immune response that involves B lymphocytes and the production of antibodies is called the humoral response

Primary immune response

• When an antigen enters the body, B cells are activated through two mechanisms

  • Antigens on the pathogen bind directly to antibody receptors on B lymphocytes

  • Antigen-presenting cells bind to antibody receptors on B lymphocytes

• These specific B cells are activated and begin to divide by mitosis – this is called clonal selection

• The B cells multiply to produce many identical copies - this is called clonal expansion

  • Some become plasma cells that make and release lots of specific monoclonal antibodies into the blood and tissues

    • Plasma cells are short-lived, but the antibodies stay in the body for some time

  • Other B cells become memory cells which stay in the blood and provide long-term immunity

• This primary immune response is slow because it takes time to make enough antibodies