Granulocytes are present in large quantities in the blood of a normal person. These are the policemen of the body who patrol different parts of the body to ensure the absence of any infection or injury. The ready availability of destructive enzymes present within their granules, helps them to act immediately. Thus, it forms the first line of immune defense against any infective or tumorous threat.
There are 3 types of granulocytes, neutrophils (neutral – non colored granules), eosinophils (red granules), and basophils (blue granules), depending on the color of their characteristic granules (after staining with a dye). During injury or infection, they concentrate at the site and release the destructive enzymes present in the granules to neutralize the infection or kill the injured cells. The remains of the dead cells and infecting organisms are sent to the lymph nodes for further processing. They also release chemical substances, which summon more white blood cells to accumulate at the site and help in containment of the infection or injury. This process is called acute inflammation, during which all the infected or injured cells are destroyed to pave the way for production of new cells.
Each type of granulocyte is effective against a particular category of infection. This is important because granulocytes can be seen under microscopes. Thus, the differential count of WBC gives us the relative dominance of a particular type of cell in blood. For example, the normal differential counts of granulocytes are
- Neutrophils – 50-60 %
- Eosinophils – 4-5 %
- Basophils – 0-1 %
A relative increase in the number of neutrophils, eosinophils, or basophils, can be easily detected and documented by a pathologist. This helps to narrow the type of infecting organism as follows
- Neutrophilia – increased neutrophil count – bacterial and fungal infection (Salmonella typhi, Candida albicans)
- Eosinophilia – increased eosinophil count – parasitic infection (hookworm, tapeworm)
- Basophilia – increased basophil count – ectoparasite infection (ticks, louse)
Hence, a differential count of WBC is always more informative and important than the total WBC count !
Certain granulocytes, like eosinophils and basophils, are highly important in mediating allergic reactions in our body. These cells are erroneously stimulated by allergens, which causes them to release their destructive enzymes. This causes destruction of normal tissues of the body and hence, can be very dangerous. An acute allergic reaction can be life threatening and is called anaphylactic reaction. It is only immediate treatment with intravenous adrenaline that can save a person’s life. So it is always important to keep a note of one’s allergies and clearly mention them wherever necessary to prevent such disasters.
However, not all injuries and infections can be contained by granulocytes. The infecting organisms posses several mechanisms to bypass this primary defense system and reach the different parts of the body or continue to thrive at the same location despite the destructive force of the granulocytes. In certain overwhelming situations, a large number of granulocytes are lost, over and above the capacity of the bone marrow to produce new granulocytes. This is the situation where the agranulocytes (lymphocytes) assume primary importance and take charge of the situation.