Polymorphonuclear leukocytes (PMN) are a type of white blood cell (WBC) that includes neutrophils , eosinophils , basophils , and mast cells . Leukocytes (leukocytes) are involved in the body's defense against infectious organisms and PNPs are a subtype of leukocytes.
Also known as granulocytes, PMNs play a central role in the innate immune system. Under normal conditions, the most common PMN is by far the neutrophil.
What does polymorphonuclear mean?
The term " polymorphonuclear " describes the different shapes and sizes of the nuclei of these cells.
PMN nuclei are composed of two or three lobes with deep compartments. This is unlike many other cells in that the nucleus has a more uniform "yolk" appearance.
PMNs are also called granulocytes or granular leukocytes because they contain and excrete granules.
The composition of the granules depends on the type of cells. In the case of neutrophils, the granules contain enzymes and antimicrobial substances that help fight infection .
In mast cells and basophils, histamine, a chemical, is released during cell degranulation (granules of destruction), causing a protective inflammatory response .
Origin of PMN
PMNs, as well as other types of white blood cells, red blood cells, and platelets , are derived (developed) from hematopoietic stem cells in the bone marrow. Blood cell lines differ from hematopoietic stem cell precursors in two different ways:
With the exception of mast cells, PMNs are found primarily in the blood. However, cells often follow chemical signals emitted by the immune system and migrate to different parts of the body where they are needed.
For example, when inflammation begins in the body, blood vessels dilate so that these cells can more easily reach the site of infection or injury. When they appear quickly, PMNs are the body's main defense against diseases and strange attacks.
PMNs are part of the nonspecific innate immune system. This means that they treat all attackers equally. The term congenital means that this system can work from birth. Cells don't need to learn to recognize invaders; they simply attack what the body considers strange.
Different PMNs have slightly different roles in health, although there are some overlaps. While a healthy response to PMNs can fight infection, an inappropriate response (such as histamine release in people with allergic asthma ) can have adverse effects.
The functions of neutrophils and other PMNs are as follows:
- Neutrophils – These cells are the body's first line of defense against bacteria, viruses, and fungal infections. When tissue is damaged, substances called chemotactic agents are released that attract neutrophils .
- Eosinophils : these cells are involved in allergic reactions as well as against parasitic infections. High eosinophil levels can be the result of other conditions, such as drug reactions or immune system disorders, such as eosinophilic esophagitis .
- Basophils : These cells also participate in allergic reactions and release histamine and other compounds that cause inflammation. Basophils are blood-borne mast cell equivalents .
- Mast cells: These cells are found in tissues and play an important role in respiratory and digestive ailments. Mast cells exist in two main subtypes: connective tissue mast cells, which cause inflammation, and mucosal mast cells, which maintain intestinal homeostasis. Histamine and other substances in these granulocytes (such as the anticoagulant heparin) help regulate the balance of the immune response .
The innate immune response is different from the acquired immune response.
In the acquired immune system, specialized immune cells learn to recognize specific invaders. The response is complex and multifaceted than the innate immune response and involves B cells and T cell lymphocytes, as well as antigen presenting cells (APC), which alert the lymphocytes to the presence of a specific foreign agent .
Abnormal PMN levels
Blood tests are measured by a complete blood count (CBC) . The reference value (RV) is used for each type of cell. Anything below the RV can be considered low and anything above the reference value can be considered high.
There are conditions that cause high or low levels of PMN in the blood.
They are called:
- Neutrophilia : High levels of neutrophils in the blood, called neutropenia, are most often caused by infections. Several types of blood cancers, including chronic myeloid leukemia, polycythemia vera , primary myelofibrosis (angiogenic myeloid metaplasia), cause an increase in the number of neutrophils, but there are many non-cancerous causes.
- Neutropenia : When there are not enough neutrophils in the body, this is called neutropenia, which can increase a person's risk of infection. Some cancer treatments can cause a decrease in neutrophil levels , resulting in chemotherapy-induced neutropenia .
- Eosinophilia : Excessive eosinophil production, called eosinophilia , can result from allergic reactions, drug reactions, or parasitic infections. Deficiency of these cells is rare.
- Basophilia : An excess of basophils, called basophilia, can occur with hypothyroidism and certain types of blood cancers. Other disorders associated with basophilia include Crohn 's disease and ulcerative colitis , each of which is classified as inflammatory bowel disease (IBD) . Low basophil counts are also not common.