Essentially, eosinophils develop from the
multipotent hematopoietic stem cells that reside in the bone marrow. While they
are some of the more rare leukocytes (making up between 1 and 4 percent of the
total white blood cells in circulation) they play an important role in
immunity particularly as initiators and propagators of various inflammatory responses
during an infection as well as in adaptive immunity.
In particular, eosinophils play an important role in defending the body against infections and parasites that invade the body. A variety of studies have shown these cells to be multifunctional given that they participate in a variety of inflammatory processes that involve bacterial, allergies, viral infections and injury of the tissue among others.
When triggered, they respond in a number
of ways including:
The secretion of a variety
of cytokines (IL-2, IL-4, IL-5,
Transforming growth factor
One of the best ways to view and identify
eosinophils involves the use of Romanowsky-stain such as the Giemsa stain. This
involves preparing a blood smear for microscopy.
When viewed under the microscope, eosinophils
will appear spherical with a light purple body (of the cytoplasm) and dark
blue/purple nucleus with two lobes (bi-lobed). Students will also be able to
see course granules in the cytoplasm of the cell that may appear reddish orange
(as dark spots)
Like basophils and neutrophils, eosinophils are
granulocytes, which means that they have granules in their cytoplasm. The large
granules contain enzymes and proteins that serve different functions with
regards to immunity.
As previously mentioned, once triggered, they release a variety of molecules that contribute to the eosinophil response.
For the most part, these molecules present pro-inflammatory effects including:
The up-regulation of
modulation and activation
Constriction of smooth
These cells also function by initiating
antigen-specific immune responses through a process where they behave like
antigen presenting cells. By releasing toxic proteins and lipids mediators from
the granules, eosinophils are also capable of not only inducing tissue damage,
but also degrading other foreign organisms in given tissue.
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