Hematology - Lecture 3: Leukocytes PDF

# Hematology - Lecture 3: Leukocytes ## Introduction White blood cells (WBCs) or leukocytes are the colorless and nucleated formed elements of blood. "Leuk" is derived from the Greek word "leukos" meaning white. The alternative spelling for leukocytes is leucocytes. Compared to RBCs, WBCs are larg...

# Hematology - Lecture 3: Leukocytes ## Introduction White blood cells (WBCs) or leukocytes are the colorless and nucleated formed elements of blood. "Leuk" is derived from the Greek word "leukos" meaning white. The alternative spelling for leukocytes is leucocytes. Compared to RBCs, WBCs are larger in size and lesser in number. These cells are important like RBCs due to their role in the defense mechanism of the body and protecting the body from invading organism by acting like soldiers. ## Comparing WBCs and RBCs WBCs differ from RBCs in many aspects. The differences between WBCs and RBCs are: - Larger - Irregular in shape - Nucleated - Many types - Granules are present is some types of WBCs - Lifespan is shorter ## Classifying Leukocytes Based on the presence or absence of granules in the cytoplasm, leukocytes are classified into two groups: 1. **Granulocytes** which have granules. 2. **Agranulocytes** which do not have granules. ### Table of Features of WBCs and RBCs | Feature | WBCs | RBCs | |---|---|---| | Color | Colorless | Red | | Number | 4,000 to 11,000/cu mm | 4.5 to 5.5 million/cu mm | | Size | Larger, Maximum diameter = 18 μ | Smaller, Maximum diameter = 7.4 μ | | Shape | Irregular | Disk-shaped and biconcave | | Nucleus | Present | Absent | | Granules | Present in some types | Absent | | Types | Many types | Only one type | | Lifespan | 1/2 to 15 days | 120 days | ### Granulocytes Depending upon the staining property of granules, granulocytes are classified into three types: 1. **Neutrophils** - with granules taking both acidic and basic stains. 2. **Eosinophils** - with granules taking acidic stain. 3. **Basophils** - with granules taking basic stain. ### Agranulocytes Agranulocytes have plain cytoplasm without granules. Agranulocytes of two types: 1. **Monocytes** 2. **Lymphocytes** ## Morphology of White Blood Cells ### Neutrophils Neutrophils are also known as polymorphs. They contain fine or small granules in cytoplasm. The granules take both acidic and basic stains. When stained with Leishman's stain (which contains acidic eosin and basic methylene blue), granules appear violet in color. The nucleus is multilobed. The number of lobes in the nucleus depends upon the age of the cell. In younger cells, the nucleus is not lobed. In older neutrophils, the nucleus has 2 to 5 lobes. The diameter of the cell is 10 to 12 μ. The neutrophils are ameboid. ### Eosinophils Eosinophils have coarse (larger) granules in the cytoplasm. They stain pink or red with eosin. The nucleus is bilobed and spectacle-shaped. The diameter of the cell varies between 10 and 14 μ. ### Basophils Basophils also have coarse granules in the cytoplasm. The granules stain purple-blue with methylene blue. The nucleus is bilobed. The diameter of the cell is 8 to 10 μ. ### Monocytes Monocytes are the largest leukocytes, with a diameter of 14 to 18 μ. The cytoplasm is clear without granules. The nucleus is round, oval and horseshoe-shaped, bean-shaped or kidney-shaped. The nucleus is placed either in the center of the cell or pushed to one side and a large amount of cytoplasm is seen. ### Lymphocytes Like monocytes, lymphocytes also do not have granules in the cytoplasm. The nucleus is oval, bean-shaped, or kidney-shaped. The nucleus occupies the whole cytoplasm. A rim of cytoplasm may or may not be seen. #### Types of Lymphocytes Depending upon the size, lymphocytes are divided into two groups: 1. **Large lymphocytes** (younger cells with a diameter of 10 to 12 μ) 2. **Small lymphocytes** (older cells with a diameter of 7 to 10 μ) Depending upon the function, lymphocytes are dived into two types: 1. **T lymphocytes** (cells concerned with cellular immunity) 2. **B lymphocytes** (cells concerned with humoral immunity) ## Normal White Blood Cell Count 1. Total WBC count (TC): 4,000 to 11,000/cu mm of blood. 2. Differential WBC count (DC) ## Variations In White Blood Cell Count ### Leukocytosis Leukocytosis refers to an increase in total WBC count. This can occur in both physiological and pathological conditions. ### Leukopenia Leukopenia refers to a decrease in total WBC count. The term "leukopenia" is generally used for pathological conditions only. ### Granulocytosis and Granulocytopenia - Granulocytosis is the abnormal increase in the number of granulocytes. - Granulocytopenia is the abnormal reduction in the number of granulocytes. ### Agranulocytosis Agranulocytosis is an acute pathological condition characterized by an absolute lack of granulocytes. ## Physiological Variations 1. **Age:** WBC count is about 20,000 per cu mm in infants and about 10,000 to 15,000 per cu mm of blood in children. In adults, it ranges between 4,000 and 11,000 per cu mm of blood. 2. **Sex:** slightly more in males than in females. 3. **Diurnal variation:** Minimum in the early morning and maximum in the afternoon. 4. **Exercise:** increases slightly. 5. **Sleep:** decreases. 6. **Emotional conditions like anxiety:** increases. 7. **Pregnancy:** increases. 8. **Menstruation:** increases. 9. **Parturition:** increases. ## Pathological Variations All types of leukocytes do not share equally in the increase or decrease of total leukocyte count. In general, neutrophils and lymphocytes vary in opposite directions. ### Leukocytosis Leukocytosis is the increase in total leukocyte (WBC) count. It occurs in conditions such as: 1. Infections 2. Allergy 3. Common cold 4. Tuberculosis 5. Glandular fever ### Leukemia Leukemia is the condition which is characterized by abnormal and uncontrolled increase in leukocyte count, more than 1,000,000/cu mm. It is also called blood cancer. ### Leukopenia Leukopenia is the decrease in the total WBC count. It occurs in the following pathological conditions: 1. Anaphylactic shock 2. Cirrhosis of liver 3. Disorders of spleen 4. Pernicious anemia 5. Typhoid and paratyphoid 6. Viral infections ### Variation in Differential Leukocyte Count Differential leukocyte count varies in specific diseases. #### Neutrophilia Neutrophilia or neutrophilic leukocytosis is the increase in neutrophil count. It occurs in the following conditions: 1. Acute infections 2. Metabolic disorders 3. Injection of foreign proteins 4. Injection of vaccines 5. Poisoning by chemicals and drugs like lead, mercury, camphor, benzene derivatives, etc. 6. Poisoning by insect venom 7. After acute hemorrhage. #### Eosinophilia Eosinophilia is the increase in eosinophil count and it occurs in: 1. Asthma and other allergic conditions 2. Blood parasitism (malaria, filariasis) 3. Intestinal parasitism 4. Scarlet fever. #### Basophilia Basophilia is the increase in basophil count and it occurs in: 1. Smallpox 2. Chickenpox 3. Polycythemia vera. #### Monocytosis Monocytosis is the increase in monocyte count and it occurs in: 1. Tuberculosis 2. Syphilis 3. Malaria 4. Kala-azar 5. Glandular fever. #### Lymphocytosis Lymphocytosis is the increase in lymphocyte count and it occurs in: 1. Diphtheria 2. Infectious hepatitis 3. Mumps 4. Malnutrition 5. Rickets 6. Syphilis 7. Thyrotoxicosis 8. Tuberculosis. #### Neutropenia Neutropenia is the decrease in neutrophil count. It occurs in: 1. Bone marrow disorders 2. Tuberculosis 3. Typhoid 4. Vitamin deficiencies 5. Autoimmune diseases. #### Eosinopenia Decrease in eosinophil count is called eosinopenia. It occurs in: 1. Cushing's syndrome 2. Bacterial infections 3. Stress 4. Prolonged administration of drugs such as steroids, ACTH, epinephrine #### Basopenia Basopenia or basophilic leukopenia is the decrease in basophil count. It occurs in: 1. Urticaria (skin disorder) 2. Stress 3. Prolonged exposure to chemotherapy or radiation therapy. #### Monocytopenia Monocytopenia is the decrease in monocyte count. It occurs in: 1. Prolonged use of prednisone (immunosuppressant steroid) 2. AIDS 3. Chronic lymphoid leukemia. #### Lymphocytopenia Lymphocytopenia is the decrease in lymphocytes. It occurs in: 1. AIDS 2. Hodgkin's disease (cancer of the lymphatic system) 3. Malnutrition 4. Radiation therapy 5. Steroid administration. ## Lifespan Of White Blood Cells The lifespan of WBCs is not constant. It depends upon the demand in the body and its function. The lifespan of these cells may be as short as half a day or as long as 3 to 6 months. ## Properties of White Blood Cells 1. **Diapedesis**: The process by which the leukocytes squeeze through narrow blood vessels. 2. **Ameboid Movement**: Neutrophils, monocytes, and lymphocytes show amebic movement, characterized by cytoplasm protrusion and shape change. 3. **Chemotaxis**: The attraction of WBCs towards injured tissues by chemical substances released at the site of injury 4. **Phagocytosis**: Neutrophils and monocytes engulf foreign bodies by phagocytosis. ## Functions of White Blood Cells Generally, WBCs play an important role in the defense mechanism. These cells protect the body from invading organisms or foreign bodies, either by destroying or inactivating them. However, in defense mechanisms, each type of WBC acts in a different way. ### Neutrophils 1. Neutrophils play an important role in the defense mechanism of the body. 2. Along with monocytes, neutrophils provide the first line of defense against invading microorganisms. 3. Granules of neutrophils contain enzymes like proteases, myeloperoxidases, elastases, and metalloproteinases. These enzymes destroy the microorganisms. 4. The granules also contain antibody-like peptides called defensins, which are antimicrobial peptides and active against bacteria and fungi. 5. The membrane of neutrophils contains an enzyme called NADPH oxidase. 6. Respiratory burst is a rapid increase in oxygen consumption by neutrophils and other phagocytic cells during the process of phagocytosis. 7. NADPH oxidase is responsible for this phenomenon. During the respiratory burst, the free radical O2 is formed. 2O2 combine with 2H+ to form H2 O2. Both O2 and H2 O2 are the oxidants having potent bactericidal action. ### Eosinophils 1. Eosinophils play an important role in the body's defense mechanism against parasites. 2. Eosinophil count increases also during allergic diseases like asthma. 3. Eosinophils are responsible for detoxification, disintegration, and removal of foreign proteins. 4. Eosinophils are neither markedly motile nor phagocytic like the neutrophils. 5. Still, eosinophils attack parasites by cytotoxic substances (eosinophil peroxidase) present in their granules. 6. Cytokines such as interleukin-4 and interleukin-5 accelerate inflammatory responses by activating eosinophils. ### Basophils 1. Basophils play an important role in healing processes. Their number increases during the healing process. 2. Basophils also play an important role in allergy or acute hypersensitivity reactions (allergy). This is because of the presence of receptors for IgE in the basophil membrane. 3. They release heparin, which is essential to prevent intravascular blood clotting. 4. They release histamine, slow-reacting substances of anaphylaxis, bradykinin, and serotonin: These substances produce acute hypersensitivity reactions by causing vascular and tissue responses. 5. Basophils also produce proteases and myeloperoxidase: These enzymes destroy the microorganisms. ### Monocytes 1. Monocytes are the largest cells among the leukocytes. 2. Like neutrophils, monocytes also are motile and phagocytic. 3. These cells wander freely through all tissues of the body. 4. Along with neutrophils, they provide the first line of defense. 5. Monocytes are the precursors of the tissue macrophages. 6. Matured monocytes stay in the blood only for a few hours. Afterward, these cells enter the tissues from the blood and become tissue macrophages. 7. Examples of tissue macrophages are Kupffer cells in the liver, alveolar macrophages in the lungs, and macrophages in the spleen. ### Lymphocytes 1. Lymphocytes play an important role in immunity. Functionally, the lymphocytes are classified into two categories, namely T lymphocytes and B lymphocytes. 2. T lymphocytes are responsible for the development of cellular immunity and B lymphocytes are responsible for the development of humoral immunity.