You may have heard the word IHC, or a doctor may have told you to do this test. So you may be wondering what this strangely named test is, and what it does. Don't worry, today we will talk about this IHC (Immunohistochemistry) test in a simple way that you can understand. This is a really important test, especially for diagnosing certain diseases.
What is IHC (Immunohistochemistry)? Let's understand it simply!
Simply put, IHC (Immunohistochemistry) is a special test that is done in a laboratory. This is done by specialist doctors called pathologists. They use this test to check if there are any signs of a disease in a tissue sample from our body. Imagine that you have something like a small tumor in your body, and the doctor takes a small piece of it and sends it to the lab to test. That is what is called a 'biopsy' . So after that biopsy piece arrives at the lab, this IHC is one of the methods that pathologists use to test it.
With this word IHC, we get some little clues to figure out what it means. Shall we take a look?
- "Immuno": This refers to our immune system . You know, our body has a system that recognizes and fights against harmful substances (such as viruses, bacteria, fungi, parasites) that enter our body (called antigens) and cancer cells. This system makes special proteins called antibodies to find and bind to those harmful substances. The IHC test uses the ability of those antibodies to find specific antigens in a tissue sample. These antibodies then stain the relevant areas of the sample. Then, when the pathologist looks through a microscope, he can clearly see the antigens that the antibodies are attached to.
- "Histo": This refers to tissue . This means that the IHC test is performed on a tissue sample.
- "Chemistry": This means chemistry. Everything in this world, including our body tissues, is made up of tiny particles. The IHC test uses a microscope to find those antibodies that we can't see with the naked eye, but that indicate the presence of a disease.
In summary, IHC is a test that uses the immune system to detect disease markers in a piece of tissue through a chemical staining method.
When is an IHC test performed?
This IHC test is often used for a variety of purposes. Let's look at some of the main ones:
- Diagnose a condition: IHC testing can help doctors confirm the exact diagnosis of a condition such as cancer . It can also help determine the type of cancer (for example, carcinoma, melanoma, or sarcoma). Sometimes, cancer can start in one place and spread to other parts of the body. This is called metastatic cancer . In such cases, IHC testing can also help determine where the cancer actually started.
- Determine prognosis: IHC testing can also help determine how aggressive a cancer is and how quickly it spreads. It is also important to determine the stage and grade of the cancer. It is with this information that your doctor will decide what treatment is best for you.
- Predict treatment response: Some cancer cells have special characteristics. IHC tests can identify these characteristics. Based on these characteristics, it is possible to predict how the cancer will respond to certain treatments. For example, breast cancer and prostate cancers can grow in response to certain hormones (e.g., estrogen, testosterone). When IHC tests identify cancers that are sensitive to such hormones, it can be determined whether they will benefit from hormone therapy.
- Monitor treatment response: IHC testing can also be used to see if the treatment you are receiving is actually helping you recover from your illness.
In addition to these things, researchers use IHC tests to find new drugs. IHC helps us learn more about how the cells in our bodies, and the tiny molecules inside those cells, work. It can also help us find out how diseases affect these processes and what treatments might help.
What diseases can be detected by IHC testing?
Doctors most often use IHC testing to diagnose cancer . But it can also help diagnose several other diseases. For example:
- Alzheimer's disease
- Parkinson's disease
- Muscular dystrophy
This method can also be used to identify various pathogens that cause infections . In fact, the first successful IHC test in history was performed in 1941. At that time, a team of researchers (Coons et al.) used this method to identify a bacteria (called `pneumococcus`) that causes pneumonia in a tissue sample. Imagine how big this must have been at the time!
How does this IHC test work?
In simple terms, an IHC test uses antibodies to detect a target antigen in a tissue sample. This target antigen is a marker that indicates the presence of a disease. It is like an antigen that fits a key (antibody). If the antibody recognizes the antigen, it binds to it. When it does, the corresponding areas of the tissue sample appear colored when viewed under a microscope.
Here's a little more explanation of how this happens:
1. The pathologist attaches an enzyme to the selected antibody. This enzyme reacts only if the antibody binds to the target antigen.
2. Then, the antibody linked to this enzyme is added to the tissue sample.
3. If the tissue sample contains that target antigen, the antibody will go and attach to it.
4. As soon as it sticks like this, that enzyme reacts.
5. Due to this reaction, the relevant areas of the tissue sample appear colored when viewed under a microscope.
For these results to be reliable , pathologists must perform every step of this test very accurately.
Preparing the sample
It is very important to prepare the sample properly. This is where the staining will take place. If an antibody is present, it should be clearly visible as a stained area, separated from the background. There are several things that pathologists do to achieve this:
- Preserve the tissue: Tissue is made up of cells. These cells die over time. So this process is controlled by ``fixing`` or preserving the tissue. This allows the structure of the tissue to remain intact, allowing for proper staining. A solution called ``formalin`` (a solution of the chemical ``formaldehyde``) is often used for this.
- Ensure antigens are accessible: Sometimes, during the process of fixing the tissue, some parts of the antigen can become covered. Then the antibody cannot go there and attach. There is a process called `antigen retrieval` , which can make those covered parts reappear and make room for the antibody to attach.
- Block similar structures: Sometimes, antibodies can bind to other structures that are similar in shape to the target antigen, but are not actually the same. Pathologists block these similar structures in advance. Then the antibody will only bind to the exact target antigen.
Selecting antibodies
Pathologists select antibodies that are known to bind to the target antigen. Two main types of antibodies are used for IHC tests:
- Polyclonal antibodies: These are a mixture of different types of antibodies. These antibodies can bind to several different binding sites on an antigen.
- Monoclonal antibodies: These are multiple copies of the same antibody. Monoclonal antibodies bind to only one specific binding site on an antigen.
Detecting the antigen
Pathologists prepare the antibody in a way that allows it to stain the tissue containing the antigen. To do this, they:
1. The antibody is linked to an enzyme. For example, enzymes called `Horseradish peroxidase` and `Alkaline phosphatase` are used.
2. Then the antibody with this enzyme is added to the tissue sample.
3. The sample is examined under a microscope.
4. If the antigen is present, it is checked for staining that indicates it.
The first successful IHC test used a similar process. But instead of attaching the antibody to an enzyme, they attached it to something called a fluorophore . A fluorophore can absorb light and re-emit it. The fluorophore stains the sample when viewed under a fluorescence microscope . This method is now considered a separate immunostaining technique, called immunofluorescence .
What are the limitations of the IHC (Immunohistochemistry) test?
There are a few minor challenges with this IHC test.
- There is no set of standard guidelines that are universally accepted for each step of this test. Because different laboratories use different methods, there can sometimes be some variations in the results.
- Also, recent research has shown that not all antibodies used for IHC do exactly what they are supposed to do. That is, they do not recognize the target antigen in the sample. If the antibodies have these problems, the test can give incorrect results. That is, they:
- False-positive results: The IHC test shows the presence of an antigen that is not actually present.
- False-negative results: The IHC test fails to detect an antigen that is actually present.
Therefore, laboratories must have strict quality controls . This is the only way to ensure that the tissue is properly protected at every step and that high-quality staining is achieved. To increase the accuracy of IHC testing, pathologists can test an unknown tissue sample by adding antibodies to a tissue known to contain the target antigen to see if it stains properly.
How accurate is the IHC (Immunohistochemistry) test?
When done properly and with proper quality control, Immunohistochemistry is a very reliable method for diagnosing cancer. One study reported that IHC can identify the initial site of metastatic cancer with an accuracy of between 70% and 90%. So that's a big deal, right?
Is IHC a biopsy?
No. But the two are related. A biopsy is when a piece of tissue is taken from the body for testing. Immunohistochemistry is a special test performed in the laboratory by a pathologist on a tissue sample that is taken that way. That is, IHC is performed on a sample taken from a biopsy.
Immunohistochemistry (IHC) testing has allowed pathologists to do something amazing. It allows them to see signs of disease that our naked eyes cannot see. IHC testing uses our own powerful fighters, called antibodies, to reveal microscopic harmful substances that cause disease. This is just one way that scientists can study, diagnose, and, most importantly, fight diseases like cancer in the laboratory.
Final Take-Home Message
Okay, so we talked a lot about IHC (Immunohistochemistry) testing today. In short:
- IHC is a special test done in a lab that looks for disease markers (specifically, antigens found on cancer cells) in a piece of tissue.
- This uses things called `antibodies` . They stick to the signs of the disease and stain those areas. Then, you can look at them under a microscope and identify the disease.
- This IHC test is very helpful in diagnosing cancer, classifying it, assessing its severity, choosing treatment, and determining whether the treatment is successful .
- This is not a biopsy, but IHC is performed on a sample taken from a biopsy.
- If the test is done correctly, you can get very accurate results .
So, if a doctor asks you to do an IHC test, now you know what it does and how important it is. It is through tests like these that doctors can gain a clear understanding of your condition and provide you with the most appropriate treatment.
` Immunohistochemistry, IHC test, cancer diagnosis, tissue samples, antibodies, antigens, pathology
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