Immunohistochemistry is a diagnostic
tool. It uses antibodies previously
marked with a substance that can be seen under the microscope. The antibodies
are specific to an antigen that the test is able to detect. These antibodies
have high affinity to their antigens so the test has high specificity, not
necessarily high sensitivity which depends on other factors.
It is widely used to detect and classify cancer cells Antibodies can be
polyclonal or monoclonal. How can this test affect treatment options for a given
disease? I will explain this through an example:
Cells, cancer or not, have, different antigens (markers) on their membranes,
such as receptors, glycoproteins, etc. This markers define populations of cells
like CD4 and CD8 T-lymphocytes and B-lymphocytes (CD-20 + or -). This markers,
when they are unique to a specific type of cell, can help not only to
differentiate them, but also to target them with specific antibodies. These
antibodies can be used for tests and also as treatments.
I will explain this through an example:
A patient comes to the office with a biopsy of his pleura, and it reports "Diffuse
large B-cell lymphoma". The immunoperoxidase shows CD20 (+) (a B cell marker)
and Bcl-6 (a marker of its origin from the germinal center).
If this patient didn't have a CD20 (+) report then he wouldn't be eligible
for Rituximab therapy and the prognosis would be far more somber.
Rituximab is a genetically engineered chimeric murine/human monoclonal
antibody that targets CD20 receptors that are present in certain B-cell non-Hodgkin
lymphomas.
Once it reaches its intended
target, it activates other immune cells and the complement system to
destroy the b-cell. It is part of the new therapies that are being
used in Hemato-oncology.
Before Rituximab, the
standard therapy for B-cell lymphoma was CHOP therapy. This therapy
had a success rate of 40% to 50%. (3-year event-free rate)
When Rituximab is used in
conjunction with CHOP chemotherapy, it has shown a success rate of up to 99%
(when used in early stages).
Now you see the difference.
However this new therapies are not
exempt of potentially hazardous effects, and this page is not intended as an
advertisement of Rituximab, but to show an example of the application of
antibodies in different settings (diagnostic and therapeutic).
Images of the markers:
Picture of the CD20 marker on a
B-cell Lymphoma
Picture of the BCL6 marker on a B-cell lymphoma
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