• 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)