A type of blood cell that is made in the bone marrow and found in the blood and lymph tissue. White blood cells are part of the body’s immune system. They help the body fight infection and other diseases. Other names White blood cells / White blood corpuscles / leucocytes / leukocytes.
WBCS are important type of cells in the mammalian / human blood. WBCS differ from the RBCs in many things.
- They do not contain any respiratory pigment / haemoglobin.
- They are nucleated living cells.
- They are active and show amoeboid movements / shape.
- They are bigger in size.
- They are much less in number.
- Their life span is shorter.
- Their functions are totally different from those of RBCs.There are several varieties of leucocytes, whereas RBCS are only of one varieties.
WBCS do not have haemoglobins. Hence, they are colourless and called leucocytes (Gr. Leuko = White) nucleus, mitochondria, and Golgi apparatus. In addition, they have centriole. But normally, they do not undergo cell division.
Leucocytes are pillar of immune system and immunity. Leucocytes are rich in nucleoprotein. They also contains lipids, glycogen, cholesterol, vitamin C and specially enzyme for hydrolysis (hydrolases).
Total Count : The average total number of white blood cells is 6000-8000 per cu mm. The normal range is 5000 to 10,000 WBCS/cu mm. The average ratio of the total WBCS with total RBCS is about 1: 700
i.e. for one WBC then are 700 RBCS. There are diurnal variations. Other factors are muscular exercise, diet, emotional stress, age, infections, operations, parasitic invasion, adrenal hormones, starvation etc.
(i) Phagocytosis :
The neutrophils and monocytes engulf, dead cells, foreign particles and bacteria. They generally digest engulfed material. This process is known as phagocytosis (Engulfing solid particles).
(ii) Antibody formation :
Lymphocytes manufacture B – globulin and y – globulin. Y – globulin (antibodies) are immune bodies. They play important role in binding with antigen and hence, the defensive mechanism of body.
(iii) Secretion of heparine
Basophils are supposed to secrete heparin which prevents intra vascular clotting.
(iv) Antihistamine function
Eosinophils are very rich in histamine. They provide defense against allergic conditions. During allergy, there is excess production of histamine – like bodies.
(v) Formation of Fibroblast :
Lymphocytes may be converted into fibroblast in an area of inflammation and thus help the process of repair.
Classification / Types of WBCS:
There are two major groups of WBCS –
- (A) Granulocytes
- (B) Agranulocytes
[A] Granulocytes / Granular Leucocytes :
Leucocytes with granular cytoplasm are known as Granulocytes. Granulocytes constitute 75% of total WBCS. On the basis of shape of nucleus and types of cytoplasmic granules, there are 3 kinds of Granulocytes.
- (1) Neutrophils
- (2) Eosinophils
- (3) Basophils
(1) Neutrophils :
They are most numerous in adult blood. They constitute about 60-70% of total WBCS. Absolute no. of neutrophils are 3000 – 6000 / Cu mm. Diameter is 10-12 um. nucleus is single but it is having many lobes about 2-6. Due to the presence of lobes in nucleus, these cells are called polymorphs or polymorphonuclear leukocyte (PMNS) or polys. Generally, cells with 3-4 lobes are found in more number.
Each lobe is connected by thin strands (connections). As the age of cell increases, the number of lobes increases. When neutrophils stained, the cytoplasm shows fine, evenly distributed, pale-violet coloured granules. The sex chromosome body (one X- chromosome in females) is a small mass, usually adjacent and attached to the nucleus. It looks like drum-stick.
They are active cells. By phagocytosis, they engulf bacteria and destroy them. (1) Neutrophil
They constitute about 2-4% of total WBCS. Absolute no. is 150-400 / Cu mm. The nucleus commonly have two lobes and stains less deeply than neutrophils.Both lobes are connected by thin / thick strands. The cytoplasm contains large, uniform-sized, oval or round shaped granules. These granules do not cover the nucleus. Eosinophilic granules stain red-orange by acidic dye. (e.g. eosine).
Eosinophils show amoeboid movement and do not have phagocytosis. They release enzyme histaminase and affect histamine. They also engulf antigen – antibody complexes. They protect against parasitic worms. (2) Eosinophil
They constitute about 0.5-1% of total WBC count. Their size is smaller than other granulocytes. It has a diameter of about 8 – 10 um. Absolute no. of basophils are 0-100/ Cu mm blood. The nucleus is having two lobes or irregular in shape. Mostly it is in the form of a letter ‘S’. The cytoplasm contains granules.
These granules are round, variable in size and they stain blue-black in colour. They commonly cover the nucleus. Basophilic granules are less numerous than eosinophils. They are actively showing amoeboid movements and non-phagocytic.
They are involved in inflammatory and reactions. They develop into mast cell and secretes substance like heparin, histamine and serotonin etc. (3) Basophil
(B) Agranulocytes / Agranular Leucocytes :
Under a light microscope, these leucocytes do not show granules in the cytoplasm. Because, these granules are very small sized and having poor staining qualities. Agranulocytes constitute 25% of total WBCS. There are two kinds of Agranulocytes :
- (1) Monocytes and
- (2) Lymphocytes.
They constitutes about 3-8 % of total WBC count. Absolute number is 350-800 monocytes / Cu mm blood. Diameter is about 14-19 µm. Hence, they are largest of the leucocytes.
The nucleus has different shapes – oval, round or kidney shaped. It stains lightly than that of the lymphocytes. It is eccentric in position. Cytoplasm is in large amount, clear and non-granular.
Monocytes migrate from blood into the tissues. Then, they enlarged and differentiate into another kind of cells Macrophages. e.g. Lung, Spleen, Liver etc. some monocytes are wandering macrophages. They reach at site of infection or inflammation. They destroy antigen/foreign bodies in large amount by phagocytosis. (1) Monocyte
They constitutes about 20 – 25 % of total WBC count. Their size ranges – between 7-15 on the size, there are two kinds of lymphocytes in blood :
- (i) Small lymphocytes,
- (ii) Large lymphocytes.
(1) Small lymphocytes:
It is slightly larger than RBCS. It has large nucleus. The nucleus is nearly spherical, having a slight indentation. It is very dense and dark due to heavy chromatin mass. It occupy major part of cell.
Cytoplasm is basophilic and it surround in the form of narrow rim around nucleus. Cytoplasm stains sky blue colour. They are most common in blood compared to large lymphocytes. Their no. decreases with age (Child 50 %, 10 years – 35 % of total WBCS).
(ii) Large lymphocytes:
They have a diameter of 12 – 15 um. The nucleus may be round, oval or kidney-shaped. The cytoplasm is proportionally more and forms a winder zone around the nucleus. It is basophilic and shows no distinct granules. They are primitive and proliferative cells. They give rise to the active small lymphocytes.
FUNCTIONS OF WBCS :
There are two major types of lymphocytes:
- (a) B-cell
- (b) T-cell.
These cells are major fighter for immune system. Antigens: A substances that stimulates an immune response. e.g. Foreign proteins, bacterial enzymes, tanins etc.
When B-cells comes in the contact of specific antigen, they develop into plasma cells. Plasma cells produce specific antibody (Igs). It binds to antigen and inactivate antigen. Hence, it protects our body. Some B-cells develop into memory cells. They can be helpful in next attack of antigens.
(b) T-cells :
They are of two types Killer cell (cytotoxic T-cells) and Helper cells. Killer (Cytotoxic) T-cells directly attack on antigen and destroy it. Helper T-cells assist both B-cells and cytotoxic T-cells. So, B-cells are stimulated to secrete antibody. In addition, it secretes the substance to attract the cytotoxic cells surrounding to antigens.
Figure : Types of WBCS Some Disorders related with WBCs :
- Normal person : 5,000 – 10,000 / Cu mm
- Leukocytosis : 10,000 – 11,000 / Cu mm
- Leukemia : 80,000 – 1,00,000/ Cu mm :
- Leukopenia :< 5,000/ Cu mm
Leukemia: This is malignant type of disease. The number of WBCS (one or more types) are greatly increased.
Acute leukemia : Immature forms of WBCS are also found in circulating blood. This is due to uncontrolled production of WBCS.
Chronic leukaemia – There is accumulation of mature leukocytes in the blood beacuse they do not die at the end of their normal life span.