WHITE BLOOD CELLS

INTRODUCTION: WBCs/ Leukocytes are colourless nucleated

cell elements. Larger and lesser in number. Important in defence mechanism of body. WBCs vs RBCs:

Larger in size. Irregular.Nucleated.Many types.Some are granulated.Shorter life span.

CLASSIFICATION: Granulocytes: Depending on staining properties

1. Neutrophils. Granules taking both acidic and basic stains.

2. Eosinophils. Acidic stain.3. Basophils. Basic stains.

Agranulocytes: Plain cytoplasm without granules.

1. Monocytes.2. Lymphocytes.

NEUTROPHILS:

Also called polymorphs. Fine small granules in cytoplasm. Take acidic and basic stain. Nucleus is multilobed. Number of lobes depend on age of the

cell. Younger cells= nucleus is not lobed. Older neutrophills= 2-5 lobes. Diameter of cells is 10-12 micron. Ameboid in shape.

EOSINOPHILS: Larger coarse granules. Stain pink or red with eosin. Bilobed/ spectacle shaped nucleus. Diameter 10-14 micron.

BASOPHILS: Coarse granules in cytoplasm. Stain purple blue with methylene blue. Nucleus is bilobed. Diameter 8-10 micron.

MONOCYTES: Largest leukocytes with 14-18 micron

diameter. Nongranulated. Nucleus is round, oval, horseshoe shaped,

bean shaped or kidney shaped. Nucleus is either in center or pushed to one

side. Large amount of cytoplasm.

LYMPHOCYTES: Nongranulated cytoplasm. Nucleus is oval, bean shaped or kidney

shaped. Nucleus occupies whole cytoplasm. A rim of cytoplasm may or may not be

seen.

TYPES OF LYMPHOCYTES: Divided on basis of size and function: 1. Size:

Large lymphocytes: Younger cells. Diameter 10-12 micron.

Small lymphocytes: older cells. Diameter 7-10 micron.

2. Function:T lymphocytes. Cellular immunity.B lymphocytes. Humoral immunity.NORMAL WBC COUNT:

Total WBC count: 4,000- 11,000

VARIATION IN WBC COUNT: Leukocytosis:

Increase in total WBC count. Can be physiological and pathological.

Leukopenia:Decrease in total WBC count. Pathological.

Granulocytosis:Abnormal increase in number of granulocytes.

Granulocytopenia:Abnormal reduction in number of granulocytes.

Agranulocytosis:Absolute lack of granulocytes. Acute pathological

condition.

PHYSIOLOGICAL VARIATIONS:

Age: Infants= 20,000/ cu mm Children= 10,000-15,000/ cu mm. Adults= 4,000-11,000/ cu mm of blood.

Sex: More in males than females.

Diurnal variation: Minimum in early morning. Maximum in afternoon.

Exercise: increase slightly. Sleep: decrease. Emotional conditions: increase. Pregnancy: increase. Mensturation: increase. Parturition: increase.

PATHOLOGICAL VARIATIONS:

Leukocytosis: Increase in total leukocytes.

Leukemia:Uncontrolled increase in WBCs. Cancer.

Leukopenia:Decrease in total WBC count.

NeutropheliaIncrease in neutrophil count

Eosinophilia Increase in eosinophil count

Basophilia: increase in basophile count

Monocytosis: increase in monocyte count.

lymphocytosis: Increase in total lymphocytes.

Neutropenia: decrease in neutrophil count.

Eosinopenia. Decrease in eosinophil count.

Basopenia: Decrease in basophile count.

Monocytopenia: Decrease in monocyte count

Lymphocytopenia: Decrease in lymphocytes.

LIFE SPAN OF WHITE BLOOD CELLS:

Not constant. Depends upon body demand.

May be half day to 3-6 months.

Functions of WBCs:Defence of body.Protection from invading organisms.Each type of WBC act in different way.

PROPERTIES OF WHITE BLOOD CELLS:

1. Diapedesis:Squeezing of WBCs through narrow blood

vessels. 2. Ameboid movement:

Neutrophils, monocytes and lymphocytes. 3. Chemotaxis:

Attraction of WBCs towards injured tissues by chemical substances released at injury site.

4. Phagocytosis:Neutrophils and monocytes engulf foreign

bodies.

NEUTROPHILS: Defence mechanism of body. Provide first line of defence along with monocytes. Free cells wander freely through tissues. Their granules contain enzymes:

Proteases, myeloperoxidases, elastases and metalloproteinases.

They destroy the micro-organisms. Have antibody like anti-microbial peptides:

Cathelicidins and defensins Membrane contains NADPH oxidase.

Activated by toxic metabolites released from infected tissues.

Responsible for bactericidal action of neutrophils. Secrete platelet-activating factor:

Aggregation of platelets during injury to blood vessels to prevent excessive blood loss.

MECHANISM OF ACTION OF NEUTROPHILS: Released from blood at injury site. New cells are produced at the progenitor cells. Move by diapedesis towards injury site due to

chemotaxis (chemo attractants). They surround the area and adhere to infected

tissues. Chemo attractants increase the adhesive nature

of neutrophils. Make them sticky and attach firmly to infected

area. 1 neutrophil = 15-20 micro-organisms at the

same time. They engulf the bacteria and destroy by

phagocytosis.

RESPIRATORY BURST: Rapid increase in oxygen consumption during

phagocytosis by neutrophils and other phagocytic cells.

NADPH oxidase is responsible for this phenomenon. Radical oxygen is formed O2- combines with 2H+ ->

H2O2

O2- and H2O2 have potent bactericidal action.

PUS AND PUS CELLS: Dead WBCs, bacteria, foreign bodies and

cellular debris form whitish yellow fluid at site of injury.

Toxins from bacteria kill WBCs which are collected at the centre of infected area.

Dead cells + plasma leaked from vessels + liquified tissue cells + RBCs ( from damaged capillaries) = PUS.

EOSINOPHILS: Defensive cells against parasites. Parasitic infections -> large number of

eosinophils produced and move towards infection site.

Count also increase during allergic reactions like asthma.

Detoxification, disintegration and removal of foreign proteins.

MECHANISM OF ACTION: Lethal substances released from granules and

released at the time of exposure to parasites and foreign proteins are:

1. Eosinophil peroxidase.helminths., bacteria and tumor cells.

2. Major basic protein.Helminths. ballooning

3. Eosinophil cationic protein.10 times more toxic. Complete distension.

Neurotoxin. 4. Eosinophil derived neurotoxins.

Myelinated nerve fibers. 5. Cytokines.

Interleukin 4 & 5. increase inflammatory process by activating eosinophils. Also kill invading organisms.

BASOPHILS: Their number increase during healing process. Allergy or acute hypersensitivity reactions. Ig E receptors on basophil membrane. Rupture and release from their granules: 1. Heparin:

Prevent intravascular blood clotting. 2. Histamine, slow reacting substances of

anaphylaxis, bradykinin and seratonin: Acute hypersensitivityy reactions

Proteases and myeloperoxidase: Destruction of micro organisms.

4. Cytokine: Accelerate inflammatory responses and kill micro

organisms.

MAST CELLS: Found along blood vessels. Prominently seen in skin, mucosa of lungs,

GIT, mouth, conjunctiva and nose. They don’t enter the blood stream. Develop in bone marrow and mature in

tissues. Play important role in hypersensitivity

reactions. After activation, release chemical mediators

into the interstitium. 1. Preformed mediators:

Already formed and stored in secretory granules. 2. Newly generated mediators:

Absent during resting condition and produced during activation.

MONOCYTES: Largest, motile phagocytic cells. Wander

freely through all tissues of the body. Provide first line of defence along with

neutrophils. They secrete:

Interleukin 1Colony stimulating factorPlatelet activating factor.

Precursors of macrophages. Mature monocytes remain in blood for few

hours then enter the tissues to form macrophages.

E.g= kuffer cells, alveolar and spleen macrophages.

LYMPHOCYTES: Immune cells 2 types: T lymphocytes:

Cellular immunity B lumphocytes.

Humoral immunity