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.

(Photo credits in References)

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 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.

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.

Neutrophils (PMNs)

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

Michigan State University

These stem cells are pluripotent, meaning they can give rise to many different types of other cells and formed elements.  Hematopoietic stem cells are found in bone marrow and notably produce:

- lymphoid progenitors 
- myeloid stem cells

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Hematopoietic Stem Cells

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

The common lymphoid progenitor matures into four mature categories of lymphocytes:

- B lymphocytes
- natural killer (NK) cells
- NK-T cells
- T lymphocytes

Common Lymphoid Progenitors

Myeloid Stem Cells

CD markers stand for clusters of differentiation, these are specific antigens on cells that help to identify the cells. Most common CD markers on lymphoid and myeloid stem cells are given below:

CD markers 

Hematopoiesis Figure (Figure 17.12). Reprinted from OpenStax Microbiology (p. 701), by N. Parker, M. Shneegurt, A.-h. Thi Tu, B. M. Forester, and P. Lister, 2016, Rice University. Copyright 2016 by Rice University.

Hematopoiesis Figure

Three major types of formed elements include:

- red blood cells/erythrocytes
- platelets/thrombocytes
- white blood cells/leukocytes

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