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Many red blood cells with a single larger cell. The larger cell is pink with a purple region that fills nearly the entire cell. The purple region is labeled perforin-containing granules.
Natural killer cell with perforin-containing granules. (credit: modification of work by Rolstad B)

Monocytes

The largest of the white blood cells, monocytes have a nucleus that lacks lobes, and they also lack granules in the cytoplasm ( [link] ). Nevertheless, they are effective phagocytes, engulfing pathogens and apoptotic cells to help fight infection.

When monocytes leave the bloodstream and enter a specific body tissue, they differentiate into tissue-specific phagocytes called macrophages and dendritic cells . They are particularly important residents of lymphoid tissue, as well as nonlymphoid sites and organs. Macrophages and dendritic cells can reside in body tissues for significant lengths of time. Macrophages in specific body tissues develop characteristics suited to the particular tissue. Not only do they provide immune protection for the tissue in which they reside but they also support normal function of their neighboring tissue cells through the production of cytokines. Macrophages are given tissue-specific names, and a few examples of tissue-specific macrophages are listed in [link] . Dendritic cells are important sentinels residing in the skin and mucous membranes, which are portals of entry for many pathogens. Monocytes, macrophages, and dendritic cells are all highly phagocytic and important promoters of the immune response through their production and release of cytokines. These cells provide an essential bridge between innate and adaptive immune responses, as discussed in the next section as well as the next chapter.

Monocytes are large cells with a large purple nucleus. There is a cluster of them in a field of smaller red blood cells. A PMN is also visible with a dark, multi-lobed nucleus. Macrophages are large cells with a defined nucleus.
Monocytes are large, agranular white blood cells with a nucleus that lacks lobes. When monocytes leave the bloodstream, they differentiate and become macrophages with tissue-specific properties. (credit left: modification of work by Armed Forces Institute of Pathology; credit right: modification of work by Centers for Disease Control and Prevention)
Macrophages Found in Various Body Tissues
Tissue Macrophage
Brain and central nervous system Microglial cells
Liver Kupffer cells
Lungs Alveolar macrophages (dust cells)
Peritoneal cavity Peritoneal macrophages
  • Describe the signals that activate natural killer cells.
  • What is the difference between monocytes and macrophages?

Key concepts and summary

  • The formed elements of the blood include red blood cells ( erythrocytes ), white blood cells ( leukocytes ), and platelets (thrombocytes ). Of these, leukocytes are primarily involved in the immune response.
  • All formed elements originate in the bone marrow as stem cells (HSCs) that differentiate through hematopoiesis .
  • Granulocytes are leukocytes characterized by a lobed nucleus and granules in the cytoplasm. These include neutrophils (PMNs) , eosinophils , and basophils .
  • Neutrophils are the leukocytes found in the largest numbers in the bloodstream and they primarily fight bacterial infections.
  • Eosinophils target parasitic infections. Eosinophils and basophils are involved in allergic reactions. Both release histamine and other proinflammatory compounds from their granules upon stimulation.
  • Mast cells function similarly to basophils but can be found in tissues outside the bloodstream.
  • Natural killer ( NK ) cells are lymphocytes that recognize and kill abnormal or infected cells by releasing proteins that trigger apoptosis.
  • Monocytes are large, mononuclear leukocytes that circulate in the bloodstream. They may leave the bloodstream and take up residence in body tissues, where they differentiate and become tissue-specific macrophages and dendritic cells .

Matching

Match each cell type with its description.

___natural killer cell A. stains with basic dye methylene blue, has large amounts of histamine in granules, and facilitates allergic responses and inflammation
___basophil B. stains with acidic dye eosin, has histamine and major basic protein in granules, and facilitates responses to protozoa and helminths
___macrophage C. recognizes abnormal cells, binds to them, and releases perforin and granzyme molecules, which induce apoptosis
___eosinophil D. large agranular phagocyte that resides in tissues such as the brain and lungs

C, A, D, B

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Match each cellular defense with the infection it would most likely target.

___natural killer cell A. virus-infected cell
___neutrophil B. tapeworm in the intestines
___eosinophil C. bacteria in a skin lesion

A, C, B

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Fill in the blank

Platelets are also called ________.

thrombocytes

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The cell in the bone marrow that gives rise to all other blood cell types is the ________.

pluripotent hematopoietic stem cell (HSC)

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PMNs are another name for ________.

neutrophils

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Kupffer cells residing in the liver are a type of ________.

macrophage

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_____________ are similar to basophils, but reside in tissues rather than circulating in the blood.

mast cells

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Short answer

Explain the difference between plasma and the formed elements of the blood.

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List three ways that a neutrophil can destroy an infectious bacterium.

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Questions & Answers

Hi, I'm new here. I'm Bello Abdul Hakeem from Nigeria.
BELLO Reply
welcome on board
Kamaluddeen
Thanks brother I'm an undergraduate. I hope to study for MBBS.
BELLO
pls guys help me out
Linda
what is limitation of plate
Linda
limitation of plate load test . there are some that should be considered while performing load test which are given below, this test is usually performed on relatively similar plate ,usually 1 or 2 square foot area the reason is that the plate of greater are the economically not feasible
yemi
Mechanism of bacterial pathogenicity
rashida Reply
Toxicity
Ibrahim
write a short note on Algea
najaatu Reply
green minutes plants organisms that are produced in turf.
Prince
Algae is a kind of a photosynthetic organism, which is usually grown in the moist areas. These are usually the simple plants that grow near to the water bodies. It contains a kind of chlorophyll pigments that act as a primary coloring agent.
Avi
they are eukaryotic and most lived in fresh water. they are photosynthetic that's, they contain chlorophyll and store starch in discrete chloroplast.
Prince
are bacteria important to man
just Reply
yes, depending on the type of bacteria .eg the normal florals, the latic acid batteries etc are important to man
Lois
I mean latic acid bacterial
Lois
I don't understand this topic
Jane Reply
what topic is that
Rose
sahi kon hai bhosri ke
saurabh Reply
define metabolism of carbohydrates with example
Thavasi Reply
what is sterilization a
Sani
the process of keep equipment free from bacteria
shar
is it only bacteria?
Lois
no undesirable fungi and contamination also.
Khushbu
what is streak plate method
Offikwu
what is the biofilm
Dimingu
metabolism is the sum of all the biochemical reaction required for energy generation and use of that energy to synthesize cell materials from small molecules in environment.
Alex
boclenia
Pooja
what are granulocytes
Shawnitta Reply
e.coli
Sukhdeep
granulocytes are type of WBCs which contains granules in the cytoplasm
Owili
suitable example for prokaryotes
Suvetha Reply
one of the possible early sources of energy was
Suvetha
uv radiation and lighting
Anisha
e coli is the example of prokaryotes
Sukhdeep
archaea too
Noel
which is the specific virus causing typhoid
Jeremiah Reply
it's caused by a virulent bacteria called Salmonella Typhi
Sarah
write the life cycle of HIV
Firomsa Reply
describe the internal and external structure of prokaryotic cell in terms of there appearance and functions
Lenia Reply
compare and contrast similar structures found in prokaryotic and eukaryotic cells
Lenia
control of microorganisms
ISTEFAZUL Reply
what is sterilization
Sani
how can a doctor treat a person affected by endospore forming bacteria in his/her wound?
Mambo Reply
define disinfectant
Sani
the process of killing
shar
the process of killing microorganisms
shar
a 28 years old woman come to your clinic with complain of fever painful genital blisters which express clear fluid when ruptured burning sensation around the bristers what is the diagnosis?
Ramadhani Reply
genital herpes caused by a virus called herpe simplex virus
Doris

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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