• 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 10
9cells/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 (<4000/
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)
Lymphocyte
• 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.
Neutrophils and Macrophages Defend
Against Infections
• Neutrophils are mature cells that can attack and destroy
bacteria even in the circulating blood.
• Tissue macrophages begin life as blood monocytes, which
are immature cells while still in the blood and have little
ability to fight infectious agents at that time. However, once
they enter the tissues, they begin to swell-sometimes
increasing their diameters as much as fivefold—to as great
as 60 to 80 µm. These cells are now called macrophages,
1- Diapedesis (Squeezing through holes of capillary wall).
2- Amaeboid Motion (neutrophils & monocyte can move through the tissues by ameboid motion)
3- Chemotaxis (are attracted to inflamed tissue areas by chemotaxis) 4- Phagocytosis (cellular ingestion of the offending agent)
1- Diapedesis (Squeezing through holes of capillary wall):
Neutrophils and monocytes can squeeze through the pores of the blood capillaries by diapedesis. That is, even though a pore is much smaller than a cell, a small portion of the cell slides through the pore at a time; the portion sliding through is momentarily constricted to the size of the pore.
2- White Blood Cells Move Through Tissue Spaces by Ameboid Motion.
Both neutrophils and macrophages can move through the tissues by ameboid motion.
3- White Blood Cells Are Attracted to Inflamed Tissue Areas by Chemotaxis.
- Many different chemical substances in the tissues cause both neutrophils and macrophages to move toward the source of the chemical. This phenomenon, is known as chemotaxis.
- When a tissue becomes inflamed, at least a dozen different products that can cause chemotaxis toward the inflamed area are formed. They include (1) some of the bacterial or viral toxins, (2)
degenerative products of the inflamed tissues themselves, (3)
several reaction products of the “complement complex” activated in inflamed tissues, and (4) several reaction products caused by
plasma clotting in the inflamed area, as well as other substances.
- Chemotaxis depends on the concentration gradient of the
chemotactic substance. The concentration is greatest near the
source, which directs the unidirectional movement of the white cells.
4- Phagocytosis
The most important function of the neutrophils and macrophages is phagocytosis,which means cellular ingestion of the offending agent. - Phagocytes must be selective of the material that is phagocytized;
otherwise, normal cells and structures of the body might be ingested. Whether phagocytosis will occur depends especially on three selective procedures.
1- Most natural structures in the tissues have smooth surfaces, which resist phagocytosis. But if the surface is rough, the likelihood of
phagocytosis is increased.
2- Most natural substances of the body have protective protein coats that repel the phagocytes. Conversely, most dead tissues and foreign particles have no protective coats, which makes them subject to
phagocytosis.
3- The immune system of the body develops antibodies against
infectious agents such as bacteria. The antibodies then adhere to the bacterial membranes and thereby make the bacteria especially
susceptible to phagocytosis.
Phagocytosis by Neutrophils
• The neutrophil first attaches itself to the particle and then projects pseudopodia in all directions around the particle.
• The pseudopodia meet one another on the opposite side and fuse (this creates an enclosed chamber that contains the phagocytized particle). • The chamber invaginates to the inside of the cytoplasmic cavity and breaks
away from the outer cell membrane to form a free-floating phagocytic vesicle (also called a phagosome) inside the cytoplasm.
• A single neutrophil can usually phagocytize (3 to 20) bacteria before the neutrophil itself becomes inactivated and dies.
Phagocytosis by Macrophages
• They are much more powerful phagocytes than neutrophils, often capable of phagocytizing as many as 100 bacteria.
• They also have the ability to engulf much larger particles, even whole red
blood cells or, occasionally, malarial parasites, whereas neutrophils are not capable of phagocytizing particles much larger than bacteria.
• After digesting particles, macrophages can extrude the residual products and often survive and function for many more months
Once Phagocytized, Most Particles Are Digested by Intracellular Enzymes
• Once a foreign particle has been phagocytized, lysosomes and other cytoplasmic granules in the neutrophil or macrophage
immediately come in contact with the phagocytic vesicle, and their membranes fuse, thereby dumping many digestive enzymes and bactericidal agents into the vesicle. Thus, the phagocytic vesicle now becomes a digestive vesicle, and digestion of the
phagocytized particle begins immediately
• Both neutrophils and macrophages contain an abundance of
Phagocyte adheres to
pathogens or debris. 1
Phagocyte forms pseudopods that eventually engulf the particles, forming a phagosome.
Lysosome fuses with the phagocytic vesicle, forming a phagolysosome.
Lysosomal
enzymes digest the particles, leaving a residual body.
Exocytosis of the vesicle removes indigestible and residual material. 2 3 4 5 Phagosome (phagocytic vesicle) Lysosome Acid hydrolase enzymes
A macrophage (purple) uses its
cytoplasmic extensions to pull rod-shaped bacteria (green) toward it.
Both Neutrophils and Macrophages Can Kill Bacteria
• Neutrophils and macrophages contain bactericidal agents that kill most bacteria even when the lysosomal enzymes fail to digest them.
• This is especially important because some bacteria have protective coats or other factors that prevent their destruction by digestive
enzymes.
• Much of the killing effect results from several powerful oxidizing agents formed by enzymes in the membrane of the phagosome or by a special organelle called the peroxisome.
• These oxidizing agents include large quantities of
superoxide(O2−), hydrogen peroxide(H2O2), and hydroxyl
ions(OH−), all of which are lethal to most bacteria, even in small
quantities.