White blood cells are the body cells which form the first line of defense mechanism & immunity system.
Because of these blood cells, body shows resistance to diseases and also neutralizes any disease causing parasite.
The WBC count in a healthy individual is 4.5 to 10.5 x 103 per micro liter. They can increase or decrease or disease conditions. Their count is indicative of immune status of the body. There 3 different types of WBC’s.
They are so divided based on their physical appearance, internal cell constituents and also staining.
They are studied using microscope by staining with suitable dies.
Types of white blood cells
Though there are 5 types, for convenience of study, they can be divided in
- Acidophils (Eosinophils) (2 -4 %)
- Basophils (0.5-1%)
- Neutrophils (60-70)’
While the Agranulocytes include the rest two types viz.
- Lymphocytes (20-25%)
- Monocytes (3-8%)
The figures in the bracket indicate their ratio among the total WBC count.
WBC cell count: The cell count for each type is as below
Neutrophils count is 2-7.5 x 103
Basophils Count is 0-0.2x 103/mcl
Eosinophils count is 0.1-0.5 x10³/mcl
Lymphocytes count is 1.5-4 x 10³/mcl
Monocytes count is 0.2-1 x 10³/mcl
Role and function of WBC in the body:
As we saw earlier, white blood cells act as body’s defense. This defense involves,
a) Prevention of infection,
b) Expulsion of disease causing agent and
c) Even repair of damaged tissues.
These above function are not performed by all the WBC types. Instead, each cell type has a specific role in the body.
Acidophils also called eosinophils are involved in repair mechanism and also allergies.
Basophils release histamine a wound healing substance. They are very low in number compared to all other WBC cells.
This process of eating is termed as engulfment. After the pathogen is engulfed, it is killed by cellular enzymes released by lysosomes within the cell. So they are first line of defense and act as police in the blood. May be this is the reason their count is very high (50 – 70%) in comparison to other cell types among WBC’s.
Lymphocytes play the next important role along with neutrophils. Unlike them, these cells identify the pathogen, synthesize and produce antibodies. These antibodies neutralize the pathogenic microbes. But for this, these cell are again differentiated as
♦ Natural killer cells.
B-Cells: These are the cells which synthesize and produce the pathogen specific antibodies. They also coordinate the immune reaction. The antibodies thus produced specifically attack those microbes and kill them.
T-cells: These cells are vital in that, they can form memory of past infections. Hence they support the use of vaccines. Without these T-cells, the use of vaccines would be impossible for us. Once any antibody is produced against antigen of a microbe, that pathogen specific antigen is memorized inside T-cells. So in case of any future infection, these cells immediately trigger immune reaction comprising of B-cell based antibody production and also neutrophil attack.
Natural killer cells: As the name indicates, they are natural killers, i.e. they kill own body cells which are infected by pathogens. In doing so, they also kill the pathogenic microbe within the infected body cell. Thus they help neutralize any hidden pathogen which are out of blood circulation.
Monocytes: These cell are called as second line of defense in the body. They form in macrophages once they reach tissues from the blood. These macrophages engulf any remnant bacteria or other microbes still present in tissues. Thus they help in complete sterilization of body tissues from pathogenic microbes.
During any disease conditions, raise in WBC count is called as leukocytosis. Rise in individual types of WBC cells also is possible.
Rise in the levels of neutrophils is called neutrophilia and decline in their count is called neutropenia.
Similarly for lymphocytes, increase in numbers is called as lymphocytosis and decrease in normal count is called lymphopenia (also lymphocytopenia).
Monocytes, neurtophils and lymphocytes are part of innate immunity as they act as cellular barriers.
Reference: Principles of Anatomy and Physiology.