Mast cells are granulocytes that play an important role in hypersensitive immune responses as well as in bacterial infections. They are functionally similar to basophils, in that they have similar granule components, release the cytokine IL-4, and play an important role in allergic inflammatory responses. Though, unlike basophils, they leave circulating blood and reside in blood vessels, nerves, and areas of the body in contact with the external environment.

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Myeloid stem cells, also called myeloid progenitors, mature into colony form unit (CFU) cells that produce their respective mature cell, including:

- neutrophils
- monocytes
- eosinophils
- basophils
- mast cells
- megakaryocytes
- erythrocytes

Myeloid Stem Cells

Some types of granulocytes include:

- neutrophils
- eosinophils
- basophils
- mast cells

Types of Granulocytes

Chaplin, D. D. (2010). Overview of the immune response. Journal of Allergy and Clinical Immunology, 125(2), S3-S23.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2923430/
doi: 10.1016/j.jaci.2009.12.980

Overview of the Immune Response

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Monocytes are granulocytes that clear microbes via phagocytosis as well as other antigens that have been labeled by immunoglobulin (Ig).  These cells are activated after neutrophils are, and they have been found to present in places with chronic inflammation and infection.  Additionally, monocytes are involved in acute inflammation and causing inflammation in granulomatous conditions, which are chronic infections.  They are able to kill microbes by producing nitric oxide and regulate adaptive immunity by producing cytokines such as IL-12 and interferon (IFN)-γ.  Monocytes can differentiate into macrophages and dendritic cells.

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Monocytes

Eosinophils are granulocytes that work against protozoa and parasites, especially helminths, which are parasitic worms. They are enhanced by the cytokine IL-5 and are consequently present in allergic responses. Their granules absorb dye eosin, and contain histamine, degradative elements, and major basic protein (MBP), the latter of which works to disrupt parasitic membrane stability.

Eosinophils

Basophils are granulocytes that are morphologically similar to eosinophils. and whose granules absorb methylene blue  These cells express high-affinity surface receptors for IgE which allow them to launch very sensitive responses, especially in the case of helminths (parasitic worms).  This response includes the release of histamine, immunological mediators, and lipid derivatives that are pro-inflammatory, edema, and smooth muscle contraction.  Because they release the cytokine IL-4, they play an important role in allergic responses.

Basophils

Mast Cells

Erythrocytes are the Red Blood Cells(RBC's)that give blood the red color. They are responsible for delivering oxygen to the tissues and carrying carbon dioxide back to the lungs. The cytoplasm of RBC's are rich in haemoglobin which carry the oxygen and carbon dioxide. They have a biconcave shape and lack a nucleus. 

Erythrocytes

Neutrophils are granulocytes that are involved in eliminating bacterial pathogens and repairing tissue. They produce large amounts of reactive oxygen species (ROS) that are toxic to bacterial pathogens. Additionally, they are found in injured tissue or tissue infected with bacteria because of their phagocytic function. This allows them to eliminate pathogens and other antigens from healing tissue. Neutrophils also play a role in immunoregulation by producing cytokines such as Tumor Necrosis Factor (TNF), interleukin (IL)-12, and certain chemokines.

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