Immunohistochemistry (IHC) is a technique that combines histological, immunological, and biochemical methods to detect specific tissue components using antigen/antibody reactions. It is widely used for diagnosing abnormal cells, understanding biomarker distribution, and conducting research on protein expression in various tissues. The technique involves careful sample preparation, the use of monoclonal and polyclonal antibodies, and various detection methods, including chromogenic and fluorescence-based reporters.

1. Immunohistochemistry (IHC)
-SAMSUDEEN.S

2. Methods of protein detection
• ELISA
• Gel Electrophoresis
• Western blot
• Immunoprecipitation
• Spectrophotometry
• Enzyme assays
• X-ray crystallography
• NMR
• Immunohistochemistry

3. Immunohistochemistry (IHC)
Immunohistochemistry (IHC) combines
histological, immunological and biochemical
techniques for the identification of specific
tissue components by means of a specific
antigen/antibody reaction tagged with a
visible label.
IHC makes it possible to visualize the
distribution and localization of specific cellular
components within a cell or tissue.

4. History
• IHC takes its name from the roots "immuno",
refer to antibodies and "histo", meaning
tissue.
• Albert Coons conceptualized and first
implemented the procedure in 1941

5. Immunohistochemical staining
• Immunohistochemical staining is widely used
in the diagnosis of abnormal cells such as
those found in cancerous tumors (or) cell
death (apoptosis).
• Immunohistochemistry is also widely used in
basic research to understand the distribution
and localization of biomarkers and
differentially expressed proteins in different
parts of a biological tissue.

6. Immunohistochemical
staining

7. Preparation of the sample
• Preparation of the sample is critical to
maintain cell morphology, tissue architecture
and the antigenicity of target epitopes. This
requires proper tissue collection, fixation and
sectioning. A solution of paraformaldehyde is
often used to fix tissue.

8. Preparing tissue slices
• The tissue may then be sliced or used whole,
dependent upon the purpose of the experiment or the
tissue itself.
• Before sectioning, the tissue sample may be
embedded in a medium, like paraffin wax or
cryomedia.
• Sections can be sliced on a variety of instruments,
most commonly a microtome, cryostat, or vibratome.
• Specimens are typically sliced at a range of 3 μm-5 μm.
The slices are then mounted on slides, dehydrated
using alcohol washes of increasing concentrations
(e.g., 50%, 75%, 90%, 95%, 100%) and cleared using a
detergent like xylene before being imaged under a
microscope.

9. Antibody types
• The antibodies used for specific detection can
be
– monoclonal antibody.
– polyclonal antibody.

10. Monoclonal Antibody
• Monoclonal antibodies are antibodies that
are made by identical immune cells that are
all clones of a unique parent cell.
• Monoclonal antibodies can have monovalent
affinity in that they bind to the same epitope.

11. Polyclonal Antibody
• Polyclonal antibodies are antibodies that are
secreted by different B cell lineages within the
body. They are a collection of immunoglobulin
molecules that react against a specific antigen,
each identifying a different epitope.

12. Sample labeling
• For immunohistochemical detection strategies,
antibodies are classified as primary or secondary
reagents.
• Primary antibodies are raised against an antigen of
interest and are typically unconjugated (unlabeled),
while secondary antibodies are raised against
immunoglobulins of the primary antibody species.
• The secondary antibody is usually conjugated to a
linker molecule, such as biotin, that then recruits
reporter molecules, or the secondary antibody itself is
directly bound to the reporter molecule.

13. Immunohistochemical reporters
• Reporter molecules vary based on the nature of the
detection method, the most popular being chromogenic and
fluorescence detection mediated by an enzyme or a
fluorophore respectively.
• With chromogenic reporters, an enzyme label reacts with a
substrate to yield an intensely colored product that can be
analyzed with an ordinary light microscope. While the list of
enzyme substrates is extensive, alkaline phosphatase (AP)
and horseradish peroxidase (HRP) are the two enzymes used
most extensively as labels for protein detection.
• An array of chromogenic, fluorogenic and chemiluminescent
substrates is available for use with either enzyme, including
DAB (3,3'-diaminobenzidine) which produce a brown or
purple staining, respectively, wherever the enzymes are
bound.

14. Target antigen detection methods
• There are 2 types of methods in targeting
antigen in Immunohistochemical staining.
• They are : Direct method & Indirect method.

15. Direct method
• The direct method is a one-step staining method
and involves a labeled antibody reacting directly with
the antigen in tissue sections. While this technique
utilizes only one antibody and therefore is simple
and rapid, the sensitivity is lower due to little signal
amplification, in contrast to indirect approaches.

16. Indirect method
• The indirect method involves an unlabeled primary antibody
(first layer) that binds to the target antigen in the tissue and a
labeled secondary antibody (second layer) that reacts with the
primary antibody. This method is more sensitive than direct
detection strategies because of signal amplification due to the
binding of several secondary antibodies to each primary
antibody if the secondary antibody is conjugated to the
fluorescent (or) enzyme Reporter.

17. Counterstains
• After immunohistochemical staining of the target
antigen, a second stain is often applied to provide
contrast that helps the primary stain stand out. Many
of these stains show specificity for specific classes of
biomolecules, while others will stain the whole cell.
• Both chromogenic and fluorescent dyes are available
for IHC to provide a vast array of reagents to fit every
experimental design, and include: hematoxylin,
Hoechst stain and DAPI (4',6-diamidino-2-
phenylindole) are commonly used.
• Hoechst can be used to stain living cells as it can pass
the cell membrane, whereas DAPI can't .

18. Examples of some commonly used markers include:
BrdU: used to identify replicating cells. Used to identify tumors
as well as in neuroscience research.
Cytokeratins: used for identification of carcinomas but may
also be expressed in some sarcomas.
CD15 and CD30 : used for Hodgkin's disease
Alpha fetoprotein: for yolk sac tumors and hepatocellular
carcinoma
CD117 (KIT): for gastrointestinal stromal tumors (GIST) and
mast cell tumors
CD10 (CALLA): for renal cell carcinoma and acute lymphoblastic
leukemia
Prostate specific antigen (PSA): for prostate cancer estrogens
and progesterone receptor (ER & PR) staining are used both diagnostically
(breast and Gynecologic tumors) as well as prognostic in breast cancer and
predictive of response to therapy (estrogen receptor)
CD20 identification of B-cell lymphomas
CD3 identification of T-cell lymphomas

19. Mapping protein expression
• Immunohistochemistry can also be used for a
more general protein profiling. The Human
Protein Atlas displays a map of protein
expression in normal human organs and tissues
and organs. The combination of
immunohistochemistry and tissue microarrays
provides protein expression patterns in a large
number of different tissue types.
• Immunohistochemistry is also used for protein
profiling in the most common forms of human
cancer.