Immunity : Phagocytic cells

Phagocytic leukocytes are specialized White blood cells – WBCs – that can eat and digest microorganisms, foreign substances, abnormal cells, cellular debris and waste products. You can consider them as the body’s garbage collectors.

First of all , lets explain what does a ” phagocyte ” mean 🙂 :

“ phago ” comes from the greek word  ” phagein ” which means “ eat “

“ Cyte ” means “ cell “

so , a phagocyte is an eating cell

the phagocyte surrounds it’s meal with cytoplasmic extensions then engulf it , then release lysozomal  enzymes & free radicals to digest it

Here is an animation that illustrates the process of Phagocytosis  🙂

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Hint : when a cell eats something ” bacteria , parasite , .. etc ” we call the process Phagocytosis , while when a cell drinks something “extra\intracellular fluids ” the process is called Pinocytosis

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In the human body exists 4 different types of leukocytes that can perform Phagocytosis :

Denderitic cells

activated Monocytes ( Macrophages )

Eosinophils

Neutrophils

a small mnemonic to help in memorizing these types is ” D-MEN ” .. ( Inspired by the movie X-MEN )

i’ll take about the basic information of each type in the lines below 🙂
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1- Dendritic cells

After phagocytosis , Dendritic cells start digesting the pathogen and breaking his body into pieces ,

Then ,  the dendritic cell cuts of a certain piece of the pathogen ” called Antigen ” and attaches that antigen on a special part of it’s surface Known as Major histo compatibility complex (MHC)

When a dendritic cell carries MHC complex \ Antigen complex it is called ” Antigen presenting cell “

now .. the dendritic antigen presenting cell presents the Antigen to the T-lymphocytes causing their activation

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identification using electronic microscope :

Notice the Numerous branched cytoplasmic extensions .. that’s why it got the name ” dendritic ” 😉

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2- Monocytes  ==> activation==> Macrophages

Monocytes work as wondering gaurds .. they circulate in the blood stream with the blood and keep starring at the body’s tissues and cells to make sure they are Okay and healthy

when Monocytes discover a bacterial infection within some tissues they diffuse out of the blood into the affected tissues , Grow in size and become 15 -20 times larger .. these activated Monocytes in the tissues are Known as Macrophages ” big eaters ” ( in greek : Macro = big & phag = phagein = eat )

Luckily , the Macrophages favourite meal is Bacteria .. so they eat up the bacteria that invade the body

Macrophages are named differently according to the type tissue they are found in ..

examples :

macrophages of liver = Kupffer cells

macrophages of skin = langerhans cells

macrophages of bone = Osteoclastic cells

Macrophages of Neurons = Glial cells

Hint : Macrophages are not found in the blood stream

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microscopical identification

Monocytes are Not granular , they have a clear cytoplasm and characterestic kidney shaped ( horse shoe ) Nucleus

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Macrophages are large leukocytic cells and found in inflamed or damaged tissues Not in blood

wanna see live macrophages & dendritic cells ? ?

watch this Video 😎

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3-Eosinophils

another type of phagocytic cells is Eosinophils

– Eosinophil’s favorite meal is Multi cellular parasites as Ascaris , anclystoma . . . etc

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microscopical identification

Eosinophils contain certain granules that are stained red with eosin dye , very charactarestic red color appears in the eosinophil’s cytoplasm when examined under the microscope .

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4- Neutrophils

Neutrophils are the first line of defence against bacterial invasions ,

The Majority of the leukocytes in the human body are Neutrophils ( 60 -70 % )

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microscopical identification

they are granulated cells like eosinophils but are not stained red with eosin .

Neutrophils have a Very characterestic loped Nucleus , that appears as separate nuclear bodies distributed in the cell when examined under the microscope

for this reason , Neutrophils are called poly morphonuclear neutrophils ” PMNs“

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>> Wishing you powerful healthy phagocytes with good appetite for all evil pathogens <<

🙂

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References :

– ” Human Physiology : From Cells to Systems ” ,  By Lauralee Sherwood

– ” Lectures in principles of pharmacology ” , text book by department of Phamacology & toxicology in my Faculty