AQA AS Biology

Revision Notes

2.5.4 The T Lymphocyte Response

The T Lymphocyte Response

  • Lymphocytes are another type of white blood cell
  • They play an important part in the specific immune response
  • They are smaller than phagocytes
  • They have a large nucleus that fills most of the cell
  • They are produced in the bone marrow before birth
  • There are two types of lymphocytes (with different modes of action). The two types of lymphocytes are:
    • T-lymphocytes (T cells)
    • B-lymphocytes (B cells)

T-lymphocytes and the cellular immune response

  • Immature T-lymphocytes leave the bone marrow to mature in the thymus
  • Mature T-lymphocytes have specific cell surface receptors called T cell receptors
  • These receptors have a similar structure to antibodies and are each specific to one antigen

_The maturation of T-lymphocytes, downloadable AS & A Level Biology revision notes

The maturation of T-lymphocytes – some become helper T cells and others become killer T cells

  • T-lymphocytes are activated when they encounter (and bind to) their specific antigen that is being presented by one of the host’s cells (host cells being the human’s own cells)
  • This antigen-presenting host cell might be a macrophage or a body cell that has been invaded by a pathogen and is displaying the antigen on its cell surface membrane
  • These activated T-lymphocytes (those that have receptors specific to the antigen) divide by mitosis to increase in number (similar to the clonal selection and clonal expansion of B-lymphocytes)
  • These T-lymphocytes differentiate into two main types of T cell:
    • helper T cells
    • cytotoxic T cells(also known as killer T cells)


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.

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