White Blood Cells: Granulocytes and Agranulocytes

• There are five types of white blood cells, divided into two main classes: granulocytes and agranulocytes

Granulocytes

• Includes neutrophils, eosinophils, and basophils

Agranulocytes

• Includes lymphocytes and monocytes

Neutrophils

• These are the most common type of WBC found in a blood smear, making up 60-70% of the total amount of WBCs
• They measure 12-14 µm in diameter
• Each has a single, multilobed nucleus with between 2 and 5 lobes
• The chromatin in the nucleus is condensed, with only a few organelles in the cytoplasm
• Neutrophils have 3 types of granules: azure granules (lysosomes), secretory granules with anti-microbial enzymes in salmon pink cytoplasm, and granules with glycoproteins and gelatinase
• They are produced in the bone marrow, circulate in the blood for 6-10 hours, and then enter the tissues
• Neutrophils are motile, phagocytic cells that destroy damaged tissue and bacteria
• These are important in inflammatory reactions

Eosinophils

• These make up 1-6% of total WBCs
• They measure 12-17 μm in diameter
• Eosinophils only have two lobes to their nucleus
• They have large acidophilic specific granules that stain bright red or reddish-purple
• Granules include toxic and destructive proteins
• Eosinophils are produced in the bone marrow and migrate from the peripheral blood system after a few hours into loose connective tissue in the respiratory and gastrointestinal tracts
• They phagocytose antigen-antibody complexes
• Eosinophils produce histaminase and aryl sulphatase B, two enzymes that inactivate inflammatory agents released by mast cells
• A high eosinophil blood count can indicate an possible allergic reaction
• Eosinophils are important in killing parasitic worms

Basophils

• They make up only 1% of the WBCs found in a blood smear
• Basophils measure 14-16 µm in diameter
• They contain many deep blue staining granules and a bilobed nucleus
• The granules contain heparin, histamine, serotonin, prostaglandins, and leukotrienes
• Basophils are involved in immune responses to parasites
• They have IgE receptors and the granules are released when the cells bind IgE
• Basophils accumulate at sites of infection
• Release of prostaglandins, serotonin, and histamine increases blood flow to the area of damage as part of the inflammatory response
• Degranulation, or the release of histamine, plays a role in allergic reactions like hay fever

Lymphocytes

• Small lymphocytes measure about 6-9µm, while large lymphocytes measure about 10-14µm
• Small lymphocytes have a small spherical nucleus and abundant dark staining condensed chromatin
• Not much cytoplasm can be seen, and what there is, is basophilic
• Lymphocytes comprise 20-50% of WBCs found in a blood smear
• There are two main types of lymphocytes: B-cells and T-cells
• B-cells develop in the bone marrow, while T cells are produced in the bone marrow, however, they mature in the thymus
• B-cells develop into plasma cells which make antibodies
• T-cells attack viruses, cancer cells, and transplants
• Larger lymphocytes have more cytoplasm, free ribosomes, and mitochondria
• Commonly, larger lymphocytes are activated lymphocytes

Monocytes

• They are the largest type of WBC, measuring up to 20µm in diameter
• Monocytes have a large eccentrically placed kidney bean shaped nucleus
• They have abundant cytoplasm, and some fine pink/purple granules in the cytoplasm
• Monocytes make up about 2-10% of leucocytes
• They circulate in the blood for 1-3 days, and then migrate into body tissues, where they transform into macrophages
• Monocytes will phagocytose dead cells and bacteria
• Some monocytes can also transform into osteoclasts
• Monocytes are important in the inflammatory response

This lesson covers the types of white blood cells including granulocytes (neutrophils, eosinophils, and basophils) and agranulocytes (lymphocytes and monocytes). It describes the structure, function, and characteristics of neutrophils. It also provides details on their production, circulation, and role in inflammatory reactions.