Leukocytes
WBC
Numbers
Different types
- The leukocytes, also called white blood cells, are the mobile units of the body’s protective system.
- They are formed partially in the bone marrow (granulocytes and monocytes and a few lymphocytes) and partially in the lymph tissue (lymphocytes and plasma cells).
- The real value of the white blood cells is that most of them are specifically transported to areas of serious infection and inflammation, thereby providing a rapid and potent
defense against infectious agents
- Leukocytes work together in two ways to prevent disease: (1) by actually destroying invading bacteria or viruses by phagocytosis (2) by forming antibodies and sensitized lymphocytes, which
may destroy or inactivate the invader
Leukocyte classification systems
Two major types of classification are used for leukocytes.
•Granulocytes - cells with specific granules that are quite evident by virtue of the fact that they have affinity for specific stains.
•Agranulocytes - blood cells that don't have obvious specifically stained cytoplasmic granules.
A. One classification system is based on appearance of the stained cell cytoplasm - whether or not visible “granules” are present
B. The second classification system is based on the morphology of the stained nucleus.
•Mononuclear - nucleus is not composed of identifiable lobes. Nucleus may be irregular.
•Polymorphonuclear - nucleus is composed of two or more distinct lobes.
General Characteristics of Leukocytes
Types of White Blood Cells
Granulocytes
- Contain specialized membrane-bound cytoplasmic granules
- Include neutrophils, eosinophils, and basophils.
Agranulocytes
- Lack obvious granules
- Include lymphocytes and monocytes
The granulocytes and monocytes protect the body
• 1 WBC /700 RBC
• The adult human being has about 7000 WBCs per microliter of blood (in comparison with 5 million RBCs)
• Total leucocyte count = 5-11 x 109 cells/mL • Function – To combat pathogens
• Only 2% of WBCs are found in blood,
• The rest are found in tissues, lymphatic fluid, skin, lungs, lymph nodes & spleen
The Differential White Blood Cell Count
Concentration of the different WBCs in the Blood
%
Neutrophils
60 -70
Lymphocytes
20 -25
Monocytes
3 - 8
Eosinophils
2 - 4
Leucocyte Disorders
• Leucopenia - low WBC count (<5000/
L)
– radiation, poisons, chemotherapy, shock, microbes → elevated risk of infection
• Leucocytosis = high WBC count (>11,000/
L)
– infection, allergy and disease – differential count
• Leukaemia = cancer of hemopoietic tissue
Genesis of WBCs- leucopoiesis
Sites of WBC formation
• Granulocytes (neutrophil, basophil, eosinophil): – bone marrow
• Agranulocytes
– lymphocytes- bone marrow, thymus, lymphoid tissues
leukopoiesis
Pluripotent stem cell
Colony forming unit
Myeloblasts
(neutrophils eosinophils basophils and monocytes)
Lymphoblasts B and T lymphocytes
NK cells
Interleukin 3 (IL-3) multipotent stem cell, most progenitor cells, many
terminally differentiated cells
T lymphocytes,
Granulocyte/ macrophage C SF (GM-CSF)
GM progenitor cells T lymphocytes, endothelial cells, fibroblasts
Granulocyte CSF (G-CSF) GM progenitor cells and neutrophils
macrophages, fibroblasts
Macrophage CSF (M-CSF) GM progenitor cells and macrophages
fibroblasts, macrophages, endothelial cells
Life Span of the White Blood Cells
Granulocytes:• 4 to 8 hrs (transit time ) in blood circulation • 4 to 5 days in tissues
• In infections life span a few hours (because the granulocytes proceed even more rapidly to the infected area, perform their functions, and, in the process, are themselves destroyed)
Lymphocytes:
• A few hrs in Blood Circulation >> Tissues >> Lymph >>> Blood (Recirculation)
Life span: weeks to months Monocytes :
• 10 to 20 hrs in blood circulation
Neutrophils (polymorphonuclear neutrophil -PMN)
• 10-12 μm in diameter
• 2 to 5 lobed nucleus - thin chromatin strands – older cells -more lobes
– young cells - band cells
• Highly mobile - 6-10 hrs in circulation • Spent up to 5 days in the tissues
Neutrophil - granules
- Neutrophils have fine or small granules in the cytoplasm. The granules take acidic and basic stains. When stained with Leishman’s stain the granules appear violet in color.
- Granules of neutrophils contain enzymes like proteases, myeloperoxidases, elastases and metalloproteinases. These enzymes destroy the microorganisms.
- The granules also contain antibody like
peptides called cathelicidins and defensins, which are antimicrobial peptides and are active against bacteria and fungi.
- Membrane of neutrophils contains an enzyme called NADPH oxidase. It is activated by the toxic metabolites released from infected
tissues. The activated NADPH oxidase is responsible for bactericidal action of
Eosinophil
• 2 to 4% of circulating WBCs
• Circulate 6 hrs before migrating to tissues • 10 to 14 microns
• Nucleus - 2 or 3 lobes
Eosinophils - granules
– Eosinophil peroxidase (for destruction of worms, bacteria and tumor cells)
– Major basic protein (for destruction of worms)
– Eosinophil cationic protein (for destruction of worms)
Basophils
• <1% of circulating WBCs • Diameter 8 to 10 microns
• Basophils also have coarse granules in the cytoplasm. The granules stain purple blue with methylene blue, obscure
nucleus
• Similar to tissue mast cells • Non-phagocytic cells
• Granules contain: – Histamine
– Serotonin (5HT) – Bradykinin
Released during allergic reactions
• Interleukin-4 (for acceleration of inflammatory response and destruction of invading organisms)
Monocyte
• Nucleus kidney / horse-shoe shaped
• Largest blood cell - diameter 14 – 18 μm • 3 to 8% of circulating WBCs
• The cytoplasm is clear without granules • Motile and phagocytic in nature
• Numbers increase during chronic bacterial infections, protozoan infections, malignancies • Circulate 8-12 hrs - migrate to tissues
Monocyte
• Monocytes secrete:
1. Interleukin-1 (IL-1) (Acceleration of inflammatory response and destruction of invading organisms)
Monocyte
• 20 to 25% of circulating WBCs; • Major cell of immune response • High nucleus:cytoplasm ratio
• Have not granules in the cytoplasm • 7-12 µm in diameter
• Depending upon the function, lymphocytes are divided into two types:
1. T lymphocytes: Cells concerned with cellular immunity.