White Blood Cells

The white blood cells (WBCs) are also known as leucocytes. WBCs are also mainly produced by adult bone marrow and contain nuclei that help with immune defence. WBCs are divided into two categories; those without granulocytes, also known as agranulocytes: which are the monocytes, T & B Lymphocytes; and those with granulocytes: the neutrophils, eosinophils and basophils.

Categories of leucocytes

Leucocyte production

The production of leucocytes is stimulated by various peptide proteins (known as cytokines) that assists in developing the leucocyte precursors (haematopoietic stem cells) into various matured leucocytes. In particular, the growth factor and interleukins help stimulate development of leucocytes from common myeloid and lymphoid type progenitor cells. Lymphoid progenitor cells are responsible for producing matured B and T-lymphocytes while myeloid progenitor cells produced the other 4 types of leucocytes. The maturation of granulocytic leucocytes (such as neutrophils, eosinophils and basophils) is stimulated by the Granulocyte Colony-Stimulating Factor (G-CSF), while the maturation of agranulocyte leucocytes is stimulated by the Monocyte Colony-Stimulating Factor (M-CSF).

Major types of WBCs: Neutrophils and Lymphocytes

The most abundant type of WBC is the neutrophil, which makes up 60-70% of the total distribution. It has a lobed nucleus with granules and mainly function as the first line of defense against foreign infection through the process of phagocytosis and digestion of pathogens such as bacteria. Lymphocytes are the second most abundant type of WBC, totaling 20-40% of the distribution. It generally has a spherical dark nucleus with pale cytoplasm and consist of 2 types. The B-lymphocytes produce antibodies against infections, while the T-lymphocytes release chemicals that destroy virus-infected cells.

Minor types of WBCs: Monocytes, Eosinophils and Basophils

Monocytes make up 2-6% of the distribution and help digest bacteria, antigen and old or damaged cells. They can transform into macrophages upon entering tissues, making it more capable of performing phagocytic processes against pathogens. Eosinophils add up another 1-4% of the distribution, functioning as parasite killers or turning off allergic responses. Lastly, basophils are the least abundant, found in about 0-0.5% of WBCs and work to release mediators of inflammation such as histamine.

Five Types of White Blood Cells
Neutrophils	Lobed nucleus with granules Makes up to 60-70% of total distribution Is the main and first line of defense against infection Phagocytise & digest bacteria
Lymphocytes	Spherical dark nucleus with pale cytoplasm Makes up to 20-40% of total distribution B-lymphocytes produce antibodies T-lymphocytes release chemicals to destroy viral infected cells
Monocytes	Dark kidney shape nucleus Makes up to 2-6% of total distribution Enter tissues to become macrophages Mainly digests bacteria, antigen and old or damaged cells
Eosinophils	Bilobed nucleus Makes up to 1-4% of total distribution Mainly functions to kill parasites Turns off allergic responses
Basophils	Bilobed nucleus, Dark granules Makes up to 0-0.5% of total distribution Turns on allergic response by releasing histamine or other inflammatory mediators

To learn more, you can watch this video on youtube: White Blood Cells Types and Functions