Leucocytes, also known as white blood cells or white corpuscles, are a vital part of the immune system. They help the body fight against infections and diseases by performing various functions, such as ingesting foreign materials, destroying harmful agents, or producing antibodies. In this article, we will explore what leucocytes are, how they are classified, and what causes their levels to change.

Leucocytes are cells that lack hemoglobin, have a nucleus, and can move around. They are produced and derived from stem cells in the bone marrow and are found throughout the body, including the blood and lymphatic system.

Leucocytes are highly specialized for their roles and do not undergo cell division in the bloodstream. However, some of them can still synthesize protein and RNA, which are essential for their functions.

Leucocytes can be classified into three main subtypes: granulocytes, lymphocytes, and monocytes. Each subtype has different characteristics and functions.

• Granulocytes have granules in their cytoplasm that contain enzymes and other substances that help them kill bacteria, fungi, parasites, and other invaders. They include neutrophils, eosinophils, basophils, and mast cells.
• Lymphocytes are responsible for the adaptive immune response, which involves recognizing specific antigens and producing antibodies or cytotoxic cells to eliminate them. They include T cells, B cells, and natural killer cells.
• Monocytes are large phagocytic cells that can ingest and destroy foreign materials and cellular debris. They can also differentiate into dendritic cells and macrophages, which present antigens to lymphocytes and secrete inflammatory mediators.

The normal range of leucocyte count in adults is between 4,500 and 11,000 per microliter of blood. However, this number can fluctuate depending on various factors, such as stress, exercise, infection, inflammation, medication, or disease.

An increase in leucocyte count above the normal range is called leukocytosis. It is usually a sign of infection or inflammation, as the body produces more leucocytes to fight off the invaders. However, it can also be caused by certain blood cancers or bone marrow disorders that affect leucocyte production or function.

A decrease in leucocyte count below the normal range is called leukopenia. It can be caused by viral infections that suppress bone marrow activity, autoimmune diseases that destroy leucocytes, chemotherapy or radiation therapy that damage bone marrow cells, or genetic disorders that impair leucocyte development or function. Leukopenia can increase the risk of infections and complications.

Leucocytes are essential for the immune system and play a key role in protecting the body from various threats. They can be classified into three main subtypes: granulocytes, lymphocytes, and monocytes. Their levels can change due to various factors and indicate different conditions. A blood test can measure the number and type of leucocytes in the blood and help diagnose or monitor infections, inflammations, or diseases.