CELLS OF THE IMMUNE SYSTEM
1. Leukocytes. Leucocytes-white blood cells, which acted as an independent single-celled organisms that can move and capture of microorganisms on their own.
A. Polymorphonuclear leukocytes. Polymorphonuclear leukocytes (PMNs) are phagocytes, which play a vital role in the fight against pathogenic bacteria that are responsible for periodontal diseases (Fig. 8-3).
1. PMNs, also known as the neutrophil phagocytic cells that actively absorb and destroy microorganisms.
2. These cells are quick response and provides the first line of defense against many common microorganisms and are essential for the control of bacterial infections.
3. Once in the blood, PMNs can move through the capillary walls into the tissues. PMNs attracts bacteria using a process called chemotaxis.
4. Cytoplasm PMN contains many granules filled strong bactericidal and digestive enzymes. These pellets (called lysosomes) can kill and digest bacterial cells after phagocytosis.
PMNs are short-lived cells that die, when they are filled with bacteria they phagocytize. Pus form where the inflammation contains many dead and dying PMNs. PMNs have a short lifespan, as a rule, less than 1 day.
6. Bacteria associated with periodontal disease are the most effective phagocytized by PMNs.
7. As a rule, each milliliter of blood contains between 3000 and 6000 PMNs. In PMN count less than 1000 cells/ml is called neutropenia and points to the increased risk of infection.
B. Monocytes/Macrophages. Macrophages are large phagocytes with a single kidney-shaped nucleus and some pellets (Fig. 8-4).
1. These white cells called monocytes, when found in the blood and macrophages, when they are found in the tissues.
2. Macrophages are highly phagocytic cells that actively absorb and destroy microorganisms (Fig. 8-5). Macrophages contain several lysosomes, which are filled with bactericidal and digestive enzymes.
3. Macrophages are slower to arrive at the site of infection than PMNs. Slower long-lived macrophages are often the most numerous cells in chronic inflammation.
4. Macrophages present the antigen to t cells. Together macrophages and t-lymphocytes play an important role in chronic inflammation.