What is the Difference Between Polymorphonuclear and Mononuclear Cells

The main difference between polymorphonuclear and mononuclear cells is that polymorphonuclear cells have several lobes in the nucleus, while mononuclear cells have a one-lobed nucleus. Polymorphonuclear cells include polymorphonucleated WBCs such as eosinophils, basophils, neutrophils, and mast cells, whereas mononuclear cells include lymphocytes and monocytes. 

Polymorphonuclear and mononuclear cells are two types of white blood cells in the blood. Their characteristic features are the difference in the nucleus. 

Key Areas Covered

1. What are Polymorphonuclear Cells
– Definition, Types, Function
2. What are Mononuclear Cells
– Definition, Types, Function
3. Similarities Between Polymorphonuclear and Mononuclear Cells
– Outline of Common Features
4. Difference Between Polymorphonuclear and Mononuclear Cells
– Comparison of Key Differences

Key Terms 

Mononuclear Cells, Polymorphonuclear Cells

What are Polymorphonuclear Cells

Polymorphonuclear cells are a type of white blood cells that contain more than one lobe in the nucleus. They include neutrophils, eosinophils, basophils, and mast cells.

Neutrophils

Neutrophils are one of the three types of granulocytes found in the blood. They contain a multi-lobed nucleus. They account for 62% of white blood cells in the circulation. Neutrophils are one of the first types of white blood cells that migrate to the site of infection. This migration occurs in response to cytokine signals in a process called chemotaxis. The main function of neutrophils is to destroy pathogens by phagocytosis. Hence, neutrophils engulf pathogens, including bacteria and fungi, found in the extracellular matrix by endocytosis. Here, the plasma membrane surrounds the pathogen, forming a vesicle. This vesicle is trafficked into a lysosome, which contains digestive enzymes for the degradation of the pathogen. Finally, neutrophils eliminate the waste of the digestion by exocytosis.

Figure 1: Polymorphonuclear Cells

Eosinophils

Eosinophils are the second type of granulocytes found in blood. They are found in the thymus, spleen, ovary, uterus, lymph nodes, and lower gastrointestinal tract. Eosinophils are involved in the triggering of inflammatory responses in allergic disorders. It is more than 500 eosinophils/mL blood in parasitic infections and other disease conditions. They also combat multicellular parasites like helminths. Responding to chemokine and cytokine signals, eosinophils migrate into inflammatory tissues. Along with basophils and mast cells, eosinophils mediate allergic responses and asthma pathogenesis. Eosinophils present antigens of the destroyed cells to T helper cells. By activating eosinophils, cytokines like TNF alpha and interleukins, growth factors like TGF beta and VEGF, and some other species are produced.

Basophils

Basophils are the third group of granulocytes in the blood. They contain the anticoagulant heparin, which prevents quick blood clotting. The enzymes in their granules are released during asthma. However, basophils are the least common in blood compared to other granulocytes. But they are the largest granulocytes. Basophils are capable of serving as phagocytes as well. They also produce serotonin and histamine, inducing inflammation. Moreover, they play a role in defending against viral infections. The action of basophils is inhibited by CD200 analogous, produced by viruses like Herpesvirus. Activated basophils secrete leukotrienes and some interleukins. Basophilia is the disease associated with basophils and is rarely found with leukemia.

Mast Cells

A mast cell refers to a type of white blood cell inside tissues. It is a granulocyte and contains a large number of small granules. These granules are filled with histamine and heparins. The main function of mast cells is to release these components to the tissue space in response to inflammation or allergic reactions. Other mast cell functions are angiogenesis, wound healing, defense against pathogens, etc. Mast cells are very similar to basophils in circulation in structure and function.

What are Mononuclear Cells

Mononuclear cells are the other white blood cells that occur in the blood. The key feature of them is the presence of a single-lobed nucleus. There are two types of mononuclear cells: lymphocytes and monocytes.

Lymphocytes

Lymphocytes are the other type of agranulocytes that account for 20-30% of the total white blood cell count. Also, they have a significantly longer lifespan when compared to the other types of blood cells. The three main types of lymphocytes are T cells, B cells, and natural killer cells.

Figure 2: Mononuclear Cells

• T cells: T cells mature in the thymus under the effect of the hormone thymosin. Around 80% of the circulating lymphocytes are T cells. Moreover, there are several types of T cells, including killer T cells, helper T cells, suppressor T cells, and memory T cells. T cells are involved in cell-mediated immunity. 
• B cells: They recognize foreign antigens and produce specific antibodies against them. Therefore, B cells are mainly involved in humoral immunity. T helper cells are responsible for activating B cells to produce antibodies. 
• Natural killer cells: This type of lymphocyte destroys infected body cells by bacteria or viruses. Additionally, the special proteins secreted by the natural killer cells are responsible for destroying the infected cells.

Monocytes

Monocytes are a type of agranulocytes that differentiate from monoblasts. Around 2-8% of the total white blood cells are monocytes. Also, the size of a monocyte is comparatively large and is three times the size of a typical red blood cell. Furthermore, the nucleus of the monocytes is also large and kidney-shaped. Moreover, monocytes are considered one of the most efficient types of phagocytes. Though they typically occur in the circulation, monocytes can invade tissues to become either macrophages or dendritic cells.  

Similarities Between Polymorphonuclear and Mononuclear Cells

• Polymorphonuclear and mononuclear cells are two types of white blood cells.
• They are nucleated cells.
• Also, they fight against infections. 

Difference Between Polymorphonuclear and Mononuclear Cells

Definition

Polymorphonuclear cells refer to white blood cells (WBC), including neutrophils, eosinophils, basophils, and mast cells. In contrast, mononuclear cells refer to blood cells with a single, round nucleus, such as lymphocytes and monocytes.

Examples

Polymorphonuclear cells include neutrophils, eosinophils, basophils, and mast cells, while mononuclear cells include lymphocytes and monocytes.

Nuclear Morphology

Polymorphonuclear cells have several lobes in the nucleus, while mononuclear cells have a one-lobed nucleus. 

Granules

Polymorphonuclear cells contain granules in the cytoplasm, while mononuclear cells do not contain granules in the cytoplasm. 

Conclusion

In brief, polymorphonuclear and mononuclear cells are two types of white blood cells that occur in the blood. They have differential morphologies in the nucleus. Polymorphonuclear cells include eosinophils, basophils, neutrophils, and mast cells. They contain a nucleus with more than one lobe. Also, they contain granules in the cytoplasm. In comparison, mononuclear cells are lymphocytes and monocytes. They contain a single lobe in the nucleus. But they do not contain granules in the cytoplasm. Therefore, the main difference between polymorphonuclear and mononuclear cells is the number of lobes in the nucleus.   

References:

1. Sargent, B. (2020, July 5). Isolation of mononuclear and polymorphonuclear leukocytes from blood with density separation media. Cell Culture Dish.

Image Courtesy:

1. “Blausen 0676 Neutrophil (crop)” By BruceBlaus – Own work (CC-BY SA 4.0) via Commons Wikimedia
2. “Blausen 0624 Lymphocyte B cell (crop)” By BruceBlaus – Own Work (CC-BY SA 4.0) via Commons Wikimedia