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Difference Between T Cells or T Lymphocytes and White Blood Cells or Leukocytes or Leucocytes

What are T Lymphocytes and Leukocytes?

Leukocyte or leucocytes is just another name for white blood cells (WBCs). On the contrary, lymphocytes or T cells are one of the types of WBCs or leukocytes.

Similarities between T cells and WBCs or Leukocytes

  • Leukocytes and T cells are both components of blood.
  • Both of them are responsible for immunity of vertebrates.
  • Also, both T cells and Leukocytes originate from the same multipotent hematopoietic stem cells.

T Lymphocytes

T lymphocytes or T cells are a type of leukocyte that are agranulocytes and arise from lymphoid stem cells. These cells carry out adaptive immunity responses in humans. 

The T cells are made in the bone marrow and include natural killer cells and are usually present in the blood and lymph tissue. The T cells cytoplasm usually does not comprise of bigger granules. Also, it is possible to recognize these cells easily as they have a big nucleus enveloped by a small amount of cytoplasm.


Leukocytes or leucocytes are WBCs that circulate through blood and body fluids. They represent less than one percent of the cells in human blood. These WBCs are larger than erythrocytes (blood cell that is made in the bone marrow) and contain nuclei inside the cell body.

Granular leukocytes or WBCs that have granular cytoplasm – neutrophils, eosinophils, and basophils. Each of these have specific responsibilities in fighting against invading pathogenic agents and other foreign substances. Among these WBCs, neutrophils are the most innumerable, followed by T cells, monocytes, eosinophils, and basophils.

Difference between T lymphocytes and leukocytes


T lymphocytes

T cells or T lymphocyte is a type of white blood cell that is a vital part of the immune system. 


Leukocytes are all the white blood cells in the blood. Leukocytes are composed of granulocytes (these are a type of WBCs that has small granules and these granules contain proteins) and agranulocytes (include T cells and monocytes, are a type of WBC that, unlike granulocytes, do not have visible granules).


T lymphocytes

T cells are of two types: 

B cells or B lymphocytes – B cells are activated by T lymphocytes and the antibody. B-cells protect against infectious pathogens (viruses and bacteria’s) by making Y-shaped proteins termed as antibodies, which are specific to each microorganism and have the potential to lock onto the surface of a capturing cell and pin it for destruction by other immune cells.

T lymphocytes – These are a type of WBC which are the major components and of extreme importance to the adaptive immune system. These destroy infected host cells and activate other immune cells, releasing cytokines and regulating the immune response.


There are five types of leukocytes: 

Basophils – Basophils have granules on their surfaces and are produced in the bone marrow. These are not very common type of granulocyte, and represent about 0.5 percent to 1 percent of circulating WBCs. However, they are the largest type of granulocyte. If basophils are low in the body, it may be due to a severe allergic reaction.

Neutrophils – These make up around forty percent to seventy percent of all white blood cells in humans and these are professional phagocytes, destroying pathogens like bacteria through phagocytosis. Range varies from 1,500-8,000 neutrophils per mm-3.

Eosinophils – Eosinophils, also called eosinophils or, less commonly, acidophiles, are specialized WBCs that boost inflammation and curb infection. These are one of the immune system components that play a significant role in protecting against multicellular parasites and certain infections in vertebrates. One-six percent of WBCs are eosinophils and the range vary from 0-450 eosinophils per mm-3. 

Lymphocytes – Lymphocytes are the last category of leukocytes, responsible for the adaptive immunity by releasing specific antibodies to a specific microorganism during host defense. T cells are involved in the humoral immunity and the differentiated plasma cells from B lymphocytes produce specific antibodies for a particular pathogen.

Monocytes – Monocytes are the only white blood cells (agranulocytes) found in leukocytes other than the T cells. These are the largest types of WBCs and can differentiate into macrophages and myeloid lineage dendritic cells. These also play a significant role in the process of adaptive immunity. There are at least 3 sub categories of monocytes in human blood based on their phenotypic receptors.

Type of immunity they facilitate

T lymphocytes

T lymphocytes are responsible for adaptive immunity


Leukocytes or leucocytes except lymphocytes are responsible for innate immunity in humans


T lymphocytes

  • Directly destroying infected host cells
  • Producing cytokines 
  • Regulating the immune response
  • Activating other immune cells


  • They safeguard against illness and disease.
  • They flow through the bloodstream to fight bacteria, viruses, and other foreign invaders that could be a severe threat to our health. 

Granulocytes vs Agranulocytes

T lymphocytes

T cells or T lymphocytes are only agranulocytes


Some leukocytes are granulocytes and some are agranulocytes


The points of difference between T lymphocytes and Leukocytes have been summarized as below:

T Lymphocytes Vs Leukocytes

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References :

[0]Fenech, M., & Morley, A. A. (1985). Measurement of micronuclei in lymphocytes. Mutation Research/Environmental Mutagenesis and Related Subjects, 147(1-2), 29-36.

[1]Fenech, M., & Morley, A. A. (1985). Measurement of micronuclei in lymphocytes. Mutation Research/Environmental Mutagenesis and Related Subjects, 147(1-2), 29-36.

[2]Hiremath, P. S., Bannigidad, P., & Geeta, S. (2010). Automated identification and classification of white blood cells (leukocytes) in digital microscopic images. IJCA special issue on “recent trends in image processing and pattern recognition” RTIPPR, 59-63.

[3]Moore, G. E., Gerner, R. E., & Franklin, H. A. (1967). Culture of normal human leukocytes. Jama, 199(8), 519-524.

[4]von Boehmer, H. (1994). Positive selection of lymphocytes. Cell, 76(2), 219-228.

[5]Image credit: https://upload.wikimedia.org/wikipedia/commons/thumb/7/7e/Immune_response_of_Lymphocytes.svg/500px-Immune_response_of_Lymphocytes.svg.png

[6]Image credit: https://commons.wikimedia.org/wiki/File:1916_Leukocyte_Key.jpg

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