While red cells are involved in the gaseous exchange, white blood cells participate in body defense.
Since they are part of our immune system, they are also called immune cells.
These control and kill the pathogen or neutralize the disease-causing parasite.
The WBC count in a healthy individual is 4.5 to 10.5 x 103 per microliter.
They can increase or decrease the disease conditions.
Their count indicates immune status and the disease state of the body.
There 3 different types of WBCs divided based on their physical appearance, internal cell constituents, and staining requirements.
They are studied using a microscope by staining with suitable dies.
Types of white blood cells
Though there are five types, for convenience of study, they can be divided in
|Granulocyte WBC Cell type
|% of total WBCs in blood
|2 -4 %
While the Agranulocytes include the rest two types, viz.
|% of total WBCs in blood
The figures indicate their ratio among the total WBC count.
WBC cell count
For pathological diagnosis, the cell count of each type is taken to determine the disease, and hence the normal range of each WBC count is as below
|Cells per Cubic microliter (mcL)
|2-7.5 x 103
|1.5-4 x 10³/mcL
|0.2-1 x 10³/mcL
Role and function of WBC in the body
As we saw earlier, white blood cells act as the body’s defense. This defense involves,
a) Prevention of infection
b) Expulsion of disease-causing agent and
c) Even repair of damaged tissues.
All the WBC types do not perform these above functions. Instead, each cell type has a specific role in the body.
Also called eosinophils, these cells are involved in repair mechanisms and allergies.
They release histamine, a wound-healing substance. They are very low in number compared to all other WBC cells.
These WBCs act as phagocytes. They eat up any pathogen organisms like bacteria, protozoa, and even viruses. They concentrate on the individual organs like lungs during infection to combat and form pus.
This process of eating is termed engulfment. After the pathogen is engulfed, it is killed by cellular enzymes released by lysosomes within the cell.
So they are the first line of defense and act as police in the blood.
Maybe this is why their count is very high (50-70%) compared to other cell types among WBCs.
They play the next important role, along with neutrophils.
Unlike them, these cells identify the pathogen and synthesize and produce antibodies.
These antibodies neutralize the pathogenic microbes. But for this, these cells are again differentiated as
♦ Natural killer cells.
These are the cells that synthesize and produce pathogen-specific antibodies. They also coordinate the immune reaction.
The antibodies specifically attack those microbes and kill them.
These cells are vital in forming a 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 an antigen of a microbe, that pathogen-specific antigen is memorized inside T-cells.
So in case of any future infection, these cells immediately trigger an immune reaction comprising B-cell-based antibody production and a neutrophil attack.
Natural killer cells
As the name indicates, they are natural killers, i.e., they kill their body cells infected by pathogens.
In doing so, they also kill the pathogenic microbe within the infected body cell.
Thus they help neutralize any hidden pathogens which are out of blood circulation.
These cells are called the 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 the complete sterilization of body tissues from pathogenic microbes.
During any disease condition, a rise in WBC count is called leukocytosis. An increase in individual types of WBC cells also is possible.
The rise in the levels of neutrophils is called neutrophilia, and a decline in their count is called neutropenia.
Similarly, for lymphocytes, an increase in numbers is called lymphocytosis, and a decrease in the average count is called lymphopenia (also lymphocytopenia).
Monocytes, neutrophils, and lymphocytes are part of innate immunity as they act as cellular barriers.