Cells of the Immune System: T Lymphocytes

This lesson covers:

  1. The different types of lymphocytes
  2. The different types of T cells 
  3. The role of T cells in the cellular response

Specific defence mechanisms

Specific defence mechanisms are slower than non-specific defences, but they produce a unique response for each type of pathogen. They also provide long-term immunity against specific pathogens.

Flowchart showing defence mechanisms including non-specific and specific responses with cellular and humoral responses.

The specific immune response depends on a type of white blood cell known as a lymphocyte. These cells are produced in the bone marrow. 


There are two types of lymphocyte: 

  • T lymphocytes or T cells - T cells mature in the thymus gland. They are involved in the cellular response where they respond to antigens presented on body cells.
  • B lymphocytes or B cells - B cells mature in the bone marrow. They are involved in the humoral response where they produce antibodies found in body fluids (or humors).

T cells

You need to know about the following types of T cell:


  1. T-helper cells

These cells have receptors on their cell-surface that bind to complementary antigens on antigen-presenting cells. They produce interleukins (a type of signalling molecule called a cytokine) which stimulate B cells or phagocytes. T-helper cells can also form memory cells or T-killer cells. 


  1. T-killer cells

These cells kill abnormal and foreign cells by producing a protein known as perforin. This protein makes holes in the cell-surface membrane, causing it to become freely permeable and causing cell death. 


  1. T-memory cells 

These cells provide long-term immunity against specific pathogens. They provide a rapid response if the body is re-infected by the same pathogen. 

Stages of the cellular response

The cellular response is so-called because T cells will only respond to antigens presented on body cells rather than antigens within body fluid.


The stages of the cellular response are as follows: 

Diagram showing the stages of the cellular response with an antigen-presenting cell and the development of T cells.

Macrophages engulf pathogens and display their antigens on the cell-surface. They are now known as antigen-presenting cells.

The cloned T cells can carry out different functions: 

  • Develop into memory cells - These circulate in the body to provide long-term immunity. 
  • Develop into T killer cells - These destroy infected cells.
  • Stimulate phagocytosis - Cells produce interleukins, which stimulate phagocytes to engulf pathogens. 
  • Stimulate division of B cells - Cells produce interleukins, which stimulate B cells to divide and produce antibodies.