leucocytes

DR NILESH KATE

MBBS,MDASSOCIATE PROF

DEPT. OF PHYSIOLOGY

LEUCOCYTESWHITE BLOOD

CELLS.

OBJECTIVES. Types of WBC and their counts Formation of WBC Morphology, life span, functions and

variations in count of WBC Applied aspects.

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INTRODUCTION Crucial in the body’s defense against pathogens

These are complete cells, with a nucleus and organelles

They lack Hb so they are colorless (i.e. white)

Able to move into and out of blood vessels (Diapedesis)

Can respond to chemicals released by damaged tissues (Chemotaxis)

Some are capable of Phagocytosis

TYPES OF LEUKOCYTES Granulocytes

Granules in their cytoplasm can be stained

Biologically active substances involved in inflammatory and allergic reactions.

Neutrophils, Eosinophil, and Basophils

TYPES OF LEUKOCYTES Agranulocytes

Lack visible cytoplasmic granules

Lymphocytes and Monocytes

TYPES OF LEUKOCYTES

LEUKOCYTE LEVELS IN THE BLOOD

Normal levels =4,000 to 11,000 cells/mm3

Abnormal leukocyte levels

Leucocytosis

Above 11,000 leukocytes/ml

Generally indicates an infection

Leucopenia

Abnormally low leukocyte level

Commonly caused by certain drugs

Figure 19.11

WHITE BLOOD CELLS

CONCEPT OF POOL There are 3 different areas in our body where different

WBCs reside1. Marrow pool: 90% neutrophils2. Blood pool: 3% 3. Tissue pool: 7% Genesis of WBCs: Leucopoiesis

In bone marrow → PHSC (Pluripotential hemopoietic stem cells) differentiates → committed stem cells → CFU-GM

Granulocytes & monocytes are formed only in bone marrow lymphocytes & plasma cells are produced in various

lymphogenous tissues

GENESIS OF WBCS (LEUKOPOIESIS):

REGULATION OF LEUCOPOIESIS

Granulopenia or Dead granulocytes and monocytes

Release G-CSF

M-CSF

GM-CSF

Interleukins IL-1, IL-3

Stimulate

Bone Marrow

Normal counts inhibit increased formation

Granulocytes, Monocytes/Macrophages Prostaglandins: Monocytes, Lactoferrin Cytokines: glycoproteins formed by monocytes and T- lymphocytes :

NEUTROPHILS: Size:10-14 µm in diam. Nucleus:

1. Multilobed (1-6 lobes) therefore called polymorphnuclear leucocytes.

2. Young cell have single horse shoe shaped nucleus.

3. As the cells grow older nucleus becomes multilobed. Lobes are connected with one another by chromatin threads.

4. Arneth count: Cytoplasm: contains neutrally stained

granules average half-life in the circulation is 6 hours

NEUTROPHILS:4 types of granules are present

1. Primary/ Azurophilic granules: less in no. enzymes like

i. myeloperoxidase, (produces HOCl for killing bacteria).

ii. lysosomal granules containing acid hydrolases, which can digest bacteria, elastase, proteinase, α-1 antitrypsin

iii. Antimicrobial proteins like cathepsin-G, Defensins- α, β

iv. Tissue destruction during inflammation

2. Secondary /Specific/peroxidase negative granules: more numerous. Contain

i. Lactoferrin-antibacterial

ii. Gelatinase, lysozyme- microbicidal, Vit B12 binding protein &

iii. Components of enzyme system that produce free radicals like H2O2, which kills the microbes.

iv. Substances that facilitates chemotaxis.

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NEUTROPHILS:3. Tertiary granules: Gelatinase, alkaline phosphatase and cytochrome-b

4. Secretory Granules: secretory vesicles contain CD3, phospholipase and tyrosine kinase

Toxic granules: During severe infections toxic coarse granules are seen. Functions:1. Phagocytosis:2. Reaction of inflammation: release leukotrienes, prostaglandins,

thromboxanes

3. Febrile Response: They contain fever producing substance, endogenous pyrogen which is an important mediator of febrile response to bacterial pyrogens.

NEUTROPHILS: These enzymes act in a cooperative fashion with the O2 –, H2O2, and HOCl formed by the action of

the NADPH oxidase and myeloperoxidase to produce a killing zone

around the activated neutrophil.

PROCESS OF PHAGOCYTOSIS (CELL EATING)

Phagocytes engulf and kill microorganisms

Steps of Phagocytosis:

1. Margination

2. Emigration and Diapedesis

3. Chemotaxis

4. Recognition and attachment(Opsonization)

5. Engulfment and creation of phagosome

6. Fusion of phagosome with lysosome

7. Destruction and digestion

8. Residual body Exocytosis

NEUTROPHIL RECRUITMENT

Selectins/Addressins ß2 –Integrin / ICAM-1

flow rolling adhesion transmigration

inflammatorymediators

Tissue Injury(e.g. Bacterial infection)

chemoattractant(e.g. IL-8, C5a), leukotrienes

• phagocytosis• oxidant production• lysosomal granules

endothelium

OPSONIZATION AND PHAGOCYTOSIS IgG and C3b opsonin proteins Fc receptors for antibody Complement receptors: (e.g. C3b) Other

receptors for collectins (eg. mannose-binding protein)

G protein-mediated responses, increased motor activity of the cell, exocytosis, respiratory burst

OPSONIZATION

RESPIRATORY BURST: NADPH OXIDASE

NADPH oxidase activation

Superoxide anion: O2-

Hydrogen peroxide: H2O2

Hydroxyl radical: OH .

Hypochlorous acid: HOCl

Myeloperoxidase = MPO

O2 + e-

2O2- + 2H+

H2O2 + Fe2+

H2O2

O2-

H2O2 + O2

OH + OH- + Fe3+

HOCl + OH-MPO

REACTIVE OXYGEN REACTIVE OXYGEN METABOLITESMETABOLITES

VARIATION IN NEUTROPHIL COUNT:

Neutrophilia: ↑ in neutrophils>10000/mm3

A. Physiological 1)After Exercise,

2)After injection of epinephrine,

3)Pregnancy, menstruation, parturition & lactation,

4)Newborn,

5)After meals,

6)Mental or emotional stress

B. Pathological 1)Acute pyogenic (pus forming)

bacterial infections,

2) Acute Rheumatic fever, Gout

2)Following tissue destruction,

i) Burns

ii) After hemorrhage,

iii) myocardial infarction, iv) After surgery

v) poisoning by lead, mercury,

NEUTROPENIA: ↓ IN NEUTROPHILS:

< 2500/mm3 In children Typhoid, paratyphoid fever Viral infection Malaria Aplasia of bone marrow Bone marrow depression due to

Chloromycetin, cytotoxic drugs X-rays & radiations Chemical poisons like arsenic

Size:10-14 µm in diam. (2%) Nucleus:

1. Usually (85%) cells ‘bilobed’.

2. Lobes are connected with one another by chromatin threads thus producing spectacle appearance.

3. Remaining 15% cells have trilobed nucleus.

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Cytoplasm: i. Acidophilic, appears light pink in

colour after staining Granular ii. Granules1. Coarse, stain bright brick red with

acidic (eosin) dye.

2. Granules do not cover the nucleus.

3. They contain very high peroxidase content (histaminase), lysozymes, ECF-A & Major Basic Protein (MBP)

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FUNCTIONS:1. Mild Phagocytosis: less

motile than

neutrophils

2. Parasitic infestations: Major Basic Protein- Larvicidal Eosinophil Cationic Protein-

bactericidal & major destroyer of helminths.

Eosinophil Peroxidase – destruction of helminths, bacteria & tumour cells

FUNCTIONS:3. Allergic reaction:

bronchial asthma & hay fever

Detoxifying inflammation inducing subs like bradykinin, histamine

inhibit mast cell degranulation phagocytose & destroy Ag-Ab

complexes

4. Immunity: specially abundant in the mucosa of respiratory tracts, GIT, urinary tract, where they provide mucosal immunity

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VARIATION IN EOSINOPHIL COUNT

Eosinophilia: ↑ in eosinophils Causes are:-

1)Allergic conditions e.g. bronchial asthma, hay fever, filariasis

2) Parasitic infestation, trichinosis & schistosomiasis e.g. worms (hookworm, roundworm & tapeworm),

3) Skin disease like utricaria.

Eosinopenia: ↓ in eosinophils

Causes are:-

1) ACTH & steroid therapy

2) Stressful conditions, &

3) Acute pyogenic infections

BASOPHILS: Size:10-14 µm in diam. Nucleus:

irregular bilobed, often ‘S’

shaped & its boundary is not clear because

of overcrowding with coarse granules.

Cytoplasm: Is slightly basophilic & appear blue, it is full of granules.

Granules: coarse, stain deep purple/blue Plenty, completely fill the cell & overload the nucleus Contain heparin, histamine & 5HT.

FUNCTIONS 1. Mild phagocytosis

2. Role in allergic reaction: Basophils release histamine,

bradykinin, slow reacting substance of anaphylaxis (SRS-A) & serotonin (5HT). These substances cause local vascular & tissue reactions that cause many allergic manifestations.

3. Prevents spread of Allergic inflammatory process

4. Liberates heparin which i. Acts as anticoagulant & keeps blood in fluid state.

ii. Activates the enzyme lipoprotein lipase which removes fat particles from the blood after fatty meal.

VARIATION IN BASOPHIL COUNT: Basophilia: ↑ in basophil

count >100/mm3 Causes are:-

1) Viral infections, e.g. influenza, small pox & chicken pox

2) Allergic diseases

3) Chronic myeloid leukemia.

Basopenia: ↓ in basophil count

Causes are:-

1) Corticosteroid therapy,

2) Drug induced reactions &

3) Acute pyogenic infections

2nd line of defence. Size: Largest WBC 18-20 µm. Nucleus:

1. Is large single, eccentric in position (present on one side of the cell).2. It is notched/ indented (kidney shaped)3. It has reticulated chromatin network.

Cytoplasm: i. Is abundant, pale blue & usually clear with no

granules.Granules: i. Sometimes contain fine purple dust like

granules called Azur granules

FUNCTIONS1. Role in phagocytosis: These are powerful phagocytes & capable

of phagocytosis as many as 100 bacteria. They also have

ability to engulf large particles such as RBCs & malarial

parasites.

2. Role in tumor immunity: kill tumor cells after sensitization by lymphocytes, play a key role in the lymphocyte – mediated immunity.

3. Synthesis of Biological Substances: synthesis complement, prostaglandin E & clot promoting factors Interleukin1 ii) Hemopoietic factors iii) TNF-α, iv)Binding proteins like transferrin,v) lysosomes, Proteases vii) Acid hydrolases

VARIATION IN COUNTMonocytosis: ↑ in monocyte

countCauses are:-

1) Certain bacterial infections, e.g. tuberculosis, syphilis & subacute bacterial endocarditis

2) Viral infections

3) Protozoal & rickettsial infections, e.g. malaria, kala azar

Monocytopenia: ↓ in monocyte count

Causes are:-

It is rare, may be seen in hypoplastic bone marrow.

2 types of lymphocytes Morphologically: small & large Functionally: T & B lymphocytes

Small lymphocytes: 7-10 µm

Nucleus rounded, cytoplasm: just rim is seen. Older cells.

Large lymphocytes: 10-14 µm Nucleus is big with indentation, definite cytoplasm is seen. Precursor of small lymphocyte.

Functional subtypes: small lymphocytes are broadly classified into

1. B lymphocyte: processed in the bone marrow, concerned with the humoral immunity.

2. T lymphocyte: processed in thymus, concerned with the cellular immunity

Functions of B lymphocytes: B lymphocytes & their derivatives, plasma cells are responsible for humoral (antigen mediated) immunity. They produce antibodies (gamma globulins).This is major mechanism against the invading organisms

by direct action by making them inactive by agglutination, precipitation, neutralization or lysis and through complement system

Functions of T lymphocytes: T lymphocytes are responsible for cellular (Cell mediated/ T

cell) immunity. T cell immunity play imp defensive role against: viral & bacterial infections tumor cells

Provide a specific immune response toinfectious diseases.

VARIATION IN LYMPHOCYTE COUNTLymphocytosis: ↑ in

lymphocyte countPhysiological

1. healthy & young children

2. female during

menstruation

Pathological: 1. Chronic infections like tuberculosis,

hepatitis & whooping cough

2. Lymphatic leukemia

3. Viral infections like chicken pox

4. Autoimmune disease like thyrotoxicosis

Lymphocytopenia: ↓ in lymphocyte count

1. Patients on corticosteroid & immunosuppressive therapy

2. Hypoplastic bone marrow

3. Widespread irradiation

4. Acquired Immuno Deficiency syndrome (AIDS)

LIFE SPAN OF WBCS Granulocytes:

after released from bone marrow, 4-8 hours circulate in blood & another 4-5 days in the tissues. Survive only for few hours in serious infection

Monocytes: 72 hrs in blood. Once in tissue they swell up to much larger size to become

tissue macrophage → in this form they can live for month.(3) Lymphocytes:

Life span for week or months depending on body’s need. They continually circulate in blood & move from blood to

tissues & from tissues to blood and again blood to tissues.

LEUKAEMIAS Malignant diseases Increase in total WBC count->50,000/mm3 Presence of immature wbcs in peripheral blood

Types of LeukaemiasTypes of Leukaemias1. Acute myeloblastic leukaemia (AML)

2. Acute lymphoblastic leukaemia (ALL)

3. Chronic myeloid leukaemia (CML)

4. Chronic Lymphoid leukaemia (CLL)

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