Blood - Composition of Blood: White Blood Cells (Leukocytes)

White blood cells (WBCs), scientifically known as leukocytes, are a vital part of the immune system. They are also referred to as immune cells or immunocytes. Their primary function is to protect the body against infectious diseases and fight off foreign invaders, such as bacteria, viruses, and other harmful pathogens. Unlike red blood cells, WBCs are generally larger and contain a nucleus. They are colourless because they do not contain haemoglobin.

WBCs are produced in the red bone marrow, the same tissue that produces red blood cells. Some types of WBCs, like lymphocytes, further develop in the lymphatic organs.

White blood cells (WBCs) are categorised into two main groups: granulocytes and agranulocytes.

A. Granulocytes

Granulocytes are a type of white blood cell that contain granules in their cytoplasm. They include three types:

1. Basophils: Involved in the body's inflammatory response. Release chemicals like histamine that help protect the body against allergens and initiate inflammation. Play a crucial role in allergic reactions and defending against parasites.
2. Eosinophils: They specialise in fighting parasitic infections and worms. Involved in the body's response to allergic reactions. Help control inflammation and can contribute to allergy-related conditions such as asthma.
3. Neutrophils: The most abundant type of WBC, making up the majority of white blood cells. Act as the body's first line of defence by quickly responding to infections. Attack and destroy bacteria and other pathogens by engulfing and digesting them (a process called phagocytosis).

B. Agranulocytes

Agranulocytes are a type of white blood cell that do not contain granules in their cytoplasm. They include:

1. Monocytes: The largest type of WBC, with the ability to transform into macrophages when they move into tissues. Help in cleaning up the body by removing dead or damaged cells and debris. Play a role in fighting infections by consuming harmful microorganisms and activating other immune cells.
2. Lymphocytes: Essential components of the immune system, responsible for long-term immunity. Include:

• B cells: They produce antibodies to neutralise pathogens.
• T cells: They destroy infected or cancerous cells and help regulate immune responses.
• Natural Killer (NK) cells: Target and kill abnormal cells, such as cancer cells or cells infected by viruses.

1. Protect the body against infections and foreign invaders.
2. Identify and destroy bacteria, viruses, and harmful microorganisms.
3. Produce antibodies to neutralise or eliminate pathogens.
4. Respond to allergens and help regulate allergic reactions.
5. Remove dead or damaged cells and clean up cellular debris.
6. Activate and coordinate other immune cells in the defence response.
7. Maintain long-term immunity and remember past infections for faster future responses.