Paraffin
Histology
Paraffin embedding is used in histology to provide a medium to cut
sections as thin as 3 microns. Paraffin embedded tissues
are well preserved, with good morphology being present in
archival blocks decades after the tissue was embedded. This
technique allows for the use of a wide variety of colored
dyes which can simplify the identification of most tissue
components. Sections from paraffin blocks can be used for
immunohistochemistry, in-situ hybridization, and PCR.
Frozen
Section Histology
Frozen
section histology provides rapid results using unfixed tissue
in as close to its natural state as possible. The morphology
of frozen sectioned tissue is adequate, though not as good as
paraffin sectioned material. Frozen sections are useful for techniques
such as: immunohistochemistry, immunofluorescence and enzyme
histochemistry. Most routine histologic stains can be performed
on frozen tissue as well.
Antigen
Retrieval
Antigen retrieval is a microwave technique that is used on de-paraffinized
sections. Application of this simple technique causes antigens
that may have been cross-linked by the fixative to become available
for binding to antibodies. In many cases the improvement in staining
has been dramatic.
Step
sections & Serial Sections
For
some investigators a single section from a paraffin or frozen
tissue block is simply not enough information. To obtain serial
sections the technician slices into the block and collects
every section and mounts them on the slide (or series of slides).
The paraffin sections tend to adhere to each other forming long
strips or ribbons. If you've ever looked at microscope slides
in an embryology course, chances are you've seen serial sections. Step
sections are a form of sampling, in that sections are collected
at specified depths in the block (e.g., every 50 µm).
Both techniques are fairly labor-intensive and can be expensive.
Commonly requested Histologic Stains
- H&E (hematoxylin and eosin):
- H&E
is the most commonly requested histologic stain. The Gill's hematoxylin/eosin
Y technique stains nuclei blue and cytoplasm, muscle and connective
tissue pink to red.
- Trichrome:
- The trichrome
stain uses a mixture of three different dyes. Tissue stained with a
trichrome stain show muscle tissue, fibrin, and collagen dyed with
three different colors (the colors are dependent on the variation
of this technique that is used). Trichrome stains are used to differentiate
between fibrous and normal tissue. This is a good stain for detecting
liver cirrhosis or fibrotic changes due to inflammation.
- PAS (periodic acid Schiff):
- The PAS
stain is used for staining polysaccharides. This stain is often used
to stain glomeruli in kidney tissue and to demonstrate glycogen in
the liver.
- Silver Stains:
- Silver
stains can be used to stain a variety of structures. These stains can
be used to selectively stain melanin, reticular fibers, fungus, spirochetes,
or basement membranes.
- Verhoff's or Orcien Stain:
- These
stains selectively dye the elastin fibers in tissue. The stains are
useful for examining lung tissues or arteries to detect the loss of
elasticity (e.g. emphysema or arterial thickening).
- Other Special Stains worth noting:
- Congo Red (stains amyloid), Alcian Blue (stains mucopolysaccherides), Mucicarmine (stains mucin), Cresyl Violet (stains nerve cells and glia), Giemsa or Wright's (stains hematopoietic cells), Oil Red O (stains lipids, can only be performed on frozen sections).
Location: AHSC 4212 Phone: 626-4415 Email: histo@u.arizona.edu |
