Introduction to White Blood Cells - The name 'white blood cell' comes from the appearance of a blood sample after centrifugation. - White cells are found in the buffy coat, a thin layer of nucleated cells between red blood cells and blood plasma. - The term 'leukocyte' directly reflects its description, derived from the Greek roots 'leuk-' meaning white and 'cyt-' meaning cell. - The buffy coat may appear green if there are large amounts of neutrophils in the sample. - Neutrophils produce the heme-containing enzyme myeloperoxidase, which gives a green color. - All white blood cells are nucleated, distinguishing them from red blood cells and platelets. - Types of leukocytes can be classified by structure (granulocytes or agranulocytes) or by cell lineage (myeloid cells or lymphoid cells). - The five main types of white blood cells are neutrophils, eosinophils, basophils, lymphocytes, and monocytes. - Monocytes and neutrophils are phagocytic, meaning they can engulf and destroy pathogens. - Granulocytes have lobed nuclei and visible cytoplasmic granules, while agranulocytes have round nuclei and no visible granules.

Neutrophils - Neutrophils are the most abundant white blood cell, constituting 60-70% of circulating leukocytes. - They are first responders to microbial infection and defend against bacterial or fungal infections. - Neutrophils have a multi-lobed nucleus, giving them the appearance of having multiple nuclei. - Their cytoplasm may look transparent due to pale lilac granules. - Neutrophils are active in phagocytosing bacteria and are present in large amounts in pus.

Lymphocytes - Lymphocytes make up 30% of white blood cells and are divided into T cells, B cells, and natural killer cells. - B cells release antibodies and assist in the activation of T cells. - T cells include helper T cells, cytotoxic T cells, gamma delta T cells, regulatory T cells, and natural killer cells. - Lymphocytes have deeply staining nuclei and play a role in both innate and adaptive immune responses. - Memory cells can last for years, while other lymphocytes have a lifespan of weeks.

Monocytes - Monocytes constitute 5.3% of white blood cells and differentiate into tissue resident macrophages. - They migrate from the bloodstream to other tissues and play a role in immune defense. - Monocytes have a kidney-shaped nucleus. - They differentiate into tissue resident macrophages, such as Kupffer cells in the liver. - The lifespan of monocytes ranges from hours to days.

Other White Blood Cells - Eosinophils compose about 2-4% of white blood cells in circulating blood. - Eosinophils primarily deal with parasitic infections and are the predominant inflammatory cells in allergic reactions. - Basophils are responsible for allergic and antigen response by releasing histamine. - Fixed macrophages in the liver, known as Kupffer cells, are an example of tissue-resident white blood cells. - Symptoms of neutropenia are associated with the underlying cause of the decrease in neutrophils. - Causes of lymphocytopenia include inherited immune deficiency, blood cell dysfunction, infectious diseases, medications, radiation, major surgery, and immune dysfunction. - An increase in the number of white blood cells in circulation is called leukocytosis. - Neutrophilia is an increase in the absolute neutrophil count in the peripheral circulation and is often secondary to inflammation. - Eosinophilia is never a normal lab finding and requires investigation into the underlying cause. - The complete blood cell count includes the overall white blood cell count and differential count, which counts each type of white blood cell. - Reference ranges for blood tests specify the typical counts in healthy individuals.