The T Lymphocyte Response (AQA A Level Biology)

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 – 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)