BLOOD CELLS OF THE INNATE IMMUNE SYSTEM
If you remember, the blood cells of the innate immune system all come from the myeloid series of white blood cells, with the exception of platelets.
| REFLECTION
Can you remember what these blood cells of the innate immune system are called? |
All these cells, except for the monocytes and the tissue macrophages, are known as GRANULOCYTES.
These cells are known as granulocytes because they appear to contain 'granules' in their cytoplasm when you look at them through a microscope.
In actual fact, these granules are 'packets' which contain numerous biologically-active molecules, including enzymes and toxins which are fatal for infecting micro-organisms.
In effect, these 'granules' are really chemical-containing 'vesicles' - like pustules inside the cell but containing these toxic enzymes rather than pus.
These vesicles and their toxic enzymes are crucial for the process of phagocytosis.
We can differentiate, under the microscope, between neutrophils, basophils, and eosinophils.
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Granulocytes that do not stain with either an acidic or alkaline dye are called neutrophils (in terms of their pH they are neutral - hence the name 'neutrophils'). |
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Eosinophils stain with acidic dyes (of which eosin is one - hence the name 'eosinophils'). |
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Basophils and Mast Cells stain with alkaline dyes - the other name for alkaline is base, hence the name 'basophils'. |
The activities of all the cells of the myeloid series can be divided into 3 categories:
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PHAGOCYTOSIS = engulfing and destroying micro-organisms |
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CYTOTOXICITY = killing micro-organisms by damaging cell membranes |
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INFLAMMATION = the body's tissue response to infection and injury |
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DO
Before we go on to look at the granulocytes in more detail, try to find out what the difference is in terms of operation or function between a monocyte and a tissue macrophage. |
NEUTROPHILS
Neutrophils are the most numerous of the white cells in the blood stream making up 50-70% of total 'white cell count'.
Neutrophils have a multi-lobed nucleus and are therefore called Polymorphonuclear Leucocytes
| Poly
= many different, morpho = shaped, nuclear = of the nucleus, Leuko =
white, cyte = cell.
Therefore, polymorphonuclear leucocyte = a white cell that has a nucleus with different shapes. |
Neutrophils live for only a few days (about 5 days).
Neutrophils do not divide and reproduce once they have entered the bloodstream.
MONOCYTES/MACROPHAGES
Monocytes & Macrophages are the largest of the white blood cells.
They characteristically have a horseshoe- or kidney-shaped nucleus.
Less than 7% of white blood cells that are found in the bloodstream are monocytes.
However, large numbers of macrophages are found in the tissues of the body.
These blood cells are highly mobile and live for a long time.
They migrate through connective tissue by squeezing through the intercellular spaces.
Specialist macrophages can be found in the liver, kidney, brain, bone, and the lymphoid system.
EOSINOPHILS, BASOPHILS & MAST CELLS
These cells appear in such small quantities that, at this stage, we will not explore them, except to say that eosinophils are important in the destruction of larger parasites (such as intestinal worms) and also have a role to play in counteracting the effects of basophils and mast cells in the process of inflammation.
In addition, basophils and mast cells are linked to inflammation, allergies, and hypersensitivity.