Leucocyte: White Blood Cells (WBC)

The different types of leucocytes present in the circulation are:

A. Granulocytes i.e. WBC with granules in their cytoplasm

                                   Percentage             Absolute count

1. Neutrophils.             50-70%                3000-6000/cumm

2. Eosinophils                1-4%                  150-300/cumm

3. Basophils                   < 1%                  10-100/cumm

B. Agranulocytes (Agranular)

1. Lymphocytes.        20-40%               1500-2700/cumm

2. Monocytes             2-8%                   300-600/cumm

Total Leucocyte Count (TLC) 

At birth : 20,000/cumm; count decreases after 2nd week, reaching normal adult value at 5-10 years. 

In adults: 4,000-11,000/cumm.

Leucopenia - TLC decreases less than 4000/cumm.

Causes

1. Starvation

2. Typhoid (enteric) fever 

3. Viral or protozoal infection

4. Bone marrow depression

Leucocytosis - TLC increases above 11,000/cumm.

Causes

1. Newborn (normal - 20,000/cumm) 

2. In the evening (Note: minimum count is seen in the morning)

3. Exercise.

4. After injection of Epinephrine/nor-epinephrine

5. Stress.

6. Pregnancy, menstruation, lactation 

7. Administration of steroids

8. Any pyogenic (acute/chronic pus forming) or pyrogenic (fever producing) infection.

Leukaemia - is a cancerous condition of blood in which TLC is usually more than 50,000/cumm and associated with immature WBCs in the peripheral smear.

(A) NEUTROPHIL

Size: 10-14 um diameter 

Nucleus

(i) Purple in colour.

(ii) Multilobed (1-6 lobes), that is why also called poly-morphonuclear leucocyte.

(iii) Young cells have single 'horse shoe shape' nucleus.

(iv) As the cells grow older nucleus become multilobed, lobes are connected with one another by chromatin threads. More are the number of lobes, more mature is the neutrophil.

Cytoplasm: Slight bluish in colour, granular.

Granules

(i) 'fine sand like particles, called 'pin point' granules.

(ii) 'neutrophilic' in nature (red-brown in colour), i.e. takes both the acidic and the basic stains, therefore, cell is called a neutrophil.

(iii) Contain large amounts of proteins and traces of lipids and nucleic acids.

(iv) Also contain varieties of enzymes which includes: glycosidases, sulpha tases, phosphatases, nucleases (ribo nuclease and de-oxy ribonuclease) and proteolytic enzymes. They can 'lyse' any type of substance, the granules are thus regarded as 'lysosomes'.

(v) In addition, all granulocytes liberate histamine and peroxidase enzyme which aids in killing ingested bacteria.

Functions

1. Phagocytosis - whenever the body gets invaded by bacteria, neutrophils are the first cells to seek out to ingest and kill the bacteria. They have been thus called the body's first line defence against bacterial infections.

2. They contain a fever-producing substance, endogenous pyrogen which is an important mediator of febrile response to bacterial pyrogens.

Neutrophilia means increase in neutrophils, causes are:

A. Physiological

1. Exercise

2. After injection of epinephrine

3. Pregnancy, menstruation and lactation

B. Pathological

1. Acute pyogenic (pus forming) infections 

2. Following tissue destruction e.g.

(i) burns

(ii) after haemorrhage

(iii) myocardial infarction

(iv) after surgery

Neutropenia means decrease in neutrophils, causes are:

1. In children (normal count: 40%)

2. Typhoid/paratyphoid fever

3. Viral infection

4. Bone marrow depression

(B) EOSINOPHIL

Size: 10-14 um diameter 

Nucleus:

(i) Purple colour.

(ii) Usually (85%) cells - 'bilobed', the two lobes are connected with chromatin thread thus producing 'spectacle' appearance.

(iii) Remaining 15% cells have 'trilobed' nucleus.

Cytoplasm :

(i) Acidophilic, therefore, appears light pink in colour. 

(ii) Granular.

Granules:

(i) Coarse.

(ii) Stains bright red with acidic (eosin) dye.

(iii) Granules do not cover the nucleus. 

(iv) They contain:

(a) 'histamine' (content is maximum) 

(b) 'lysozymes' i.e. most of the enzy mes found in neutrophil granules, and

(c) Eosinophil chemotactic factor of anaphylaxis ECF-A.

Functions

1. Mild phagocytosis because less motile than neutrophils.

2. ECF-A is a chemical mediator of immediate hypersensitivity reactions. These range from mild urticaria to severe anaphylactic shock.

3. Eosinophils collect at the sites of allergic reaction and lim their intensity by degrading the effects of mediators (e.g. histamine, bradykinin) and inhibit mast cell degranula tion.

4. They enter the tissues and are specially abundant in the mucosa of respiratory tract, gastrointestinal and urinary tract, where they probably provide mucosal immunity. 

5. Eosinophils attack parasites that are too large to be engulfed by phagocytosis. Eosinophil granules release chemicals which are toxic to larvae of parasites.

Eosinophilia i.e. increase in eosinophils.

Causes

1. Allergic conditions e.g. bronchial asthma. 

2. Parasitic infestation e.g. worms.

3. Skin diseases

Eosinopenia i.e. decrease in eosinophils. Seen after injection of ACTH or corticosteroids because of increased sequestration of eosinophils in the lungs and spleen and by their destruction in the circulating blood.

(C) BASOPHIL

Size: 10-14 um diameter.

Nucleus: As in Eosinophil. 

Cytoplasm: Slight basophilic, therefore, appears blue; granular.

Granules:

(i) Coarse

(ii) Stains purple or blue with basic (methylene blue) dye. (iii) Granules are plenty in number and overcrowd the nucleus resulting in obscure boundary of the nucleus.

(iv) Contain histamine and heparin.

Functions

1. Mild phagocytosis.

2. Liberates histamine which leads to allergic manifestations.

3. Liberates heparin which:

(i) acts as anti-coagulant and keeps the blood in fluid state in the body;

(ii) activates a hormone, lipoprotein lipase which facilitates absorption of triglycerides after meals.

Basophilia i.e. increase in basophils.

Causes

1. Chickenpox

2. Smallpox

3. Tuberculosis

4. Influenza

Basopenia i.e. decrease in basophils.

Causes

1. After administration of gluco-corticoids. 

2. Drug induced reactions.

(D) LYMPHOCYTES

They are of two types: 

(1) Large lymphocytes: 10-14 um diameter; precursor of small lymphocytes. 

(2) Small lymphocytes (B-type): 7-10 μm diameter; responsible for 'antibody' production. Both large and small lymphocytes have the same structure.

Nucleus : 

(i) Single; very big; purple in colour. 

(ii) Shape: round, oval or indented.

(iii) Central in position and occupies whole of the cell leaving marginal cytoplasm at one end of it or all around it.

(iv) Nuclear chromatin is coarse and lumpy (shapeless). 

Cytoplasm :

(i) Pale blue

(ii) Scanty, its amount is always less than the amount of the nucleus.

Functions

Produce antibodies i.e. immune substances, specially in delayed hypersensitivity.

Lymphocytosis i.e. increase in lymphocytes.

Causes

1. In children - lymphocytes (60%) are more than neutrophils (40%), called Relative Lymphocytosis.

2. Chronic infections e.g. tuberculosis (TB). 

3. Lymphatic leukaemia.

4. Viral infections.

Lymphopenia i.e. decrease in lymphocytes.

Causes

1. Hypoplastic bone marrow

2. AIDS (acquired immuno deficiency syndrome).

(E) MONOCYTE - largest WBC

Size: 10-18 um diameter with irregular cell outline.

Nucleus : 

(i) Pale staining.

(ii) Single.

(iii) Round or indented (kidney shaped).

(iv) Eccentric in position i.e. present on one side of the cell.

(v) Nuclear chromatin is finely reticular. 

Cytoplasm: Usually pale blue; clear. 

Granules : Sometimes contains fine purple dust like granules, called Azur granules which may be few or numerous.

Functions

1. Active phagocytosis. Monocytes follow the neutrophils in the area of infections or inflammation and constitute a second line defence. Phagocytic mechanism is same as seen in neutrophils.

2. Monocytes enter the circulation from bone marrow but after 72 hours they enter the tissues to become 'tissue macrophages'. All tissue macrophages come from circulating monocytes.

3. Monocytes may also kill tumour cellsafter sensitization by lymphocytes.

4. They synthesize complement and other biologically important substances.

Monocytosis i.e. increase in monocytes.

Causes

1. Tuberculosis

2. Syphilis

3. Some leukaemias.

Monocytopenia i.e. decrease in monocytes. 

Causes: Hypoplastic bone marrow.