Celiac disease diagnosis consists of various examinations. On the one hand, tissue samples are taken from the small intestine during a gastroscopy. On the other hand, blood tests are performed to determine celiac-specific antibodies. In this article, you will learn the basics of how our immune system works and which antibodies are used in celiac disease diagnostics. 

What exactly are antibodies and what is their function?

Our immune system is highly complex, protecting the body against attacks from external pathogens and foreign substances in various ways. This can only be described in a very simplified manner here. Roughly speaking, there are two systems that operate at different speeds and with different levels of specialization. On one hand, there are general (non-specific) immune responses that can react very quickly to an intruder, for example, by releasing inflammatory mediators. These are available from birth. It is therefore also called the innate immune system.

On the other hand, the body can produce specific antibodies that are precisely targeted at one particular pathogen. This takes a little longer but is then very effective and targeted. This is the adaptive immune system, which is constantly "learning" throughout life – every time it comes into contact with a new pathogen or foreign substance. This is why children, especially at preschool age, are sick so often. Their immune system has not yet encountered many viruses, but they are constantly exposed to new germs through contact with others. It is an important life process for the immune system to engage with various infections.

What about celiac disease?

In celiac disease, too, both sides of your immune system are involved. On the one hand, many non-specific inflammatory messengers are released, which trigger inflammation in the lining of the small intestine and thereby damage the mucosal cells. On the other hand, specific antibodies are produced. They are an important diagnostic tool for identifying celiac disease and subsequently monitoring a gluten-free diet. Celiac antibodies are distinguished between those of the IgA and IgG classes. However, their actual effects on the overall disease process have not yet been fully researched.

Which antibodies are present in celiac disease? 

Historically, the (native) gliadin antibodies were first discovered in the 1970s. They target gluten fragments that are produced during digestion in the gut and absorbed by the mucous membrane. Since the gliadin chains have not yet been modified by digestive enzymes, this is referred to as native (unaltered) gliadin. The diagnostic value of this antibody group is very limited, and it is therefore no longer used today, as there are significantly better tests available. 

Since the mid-1980s, the endomysial antibody test (usually abbreviated as EmA) has been used. It has greatly improved the diagnosis of celiac disease and is still used today due to its high diagnostic value. However, the test procedure is relatively complex and requires an experienced laboratory to be performed and evaluated correctly.  

Since the late 1990s, the tissue transglutaminase antibody test has become the standard. This test essentially detects the same thing as the endomysial antibody, but with an easier-to-perform test procedure. The transglutaminase IgA antibody (usually abbreviated as tTG-IgA-Ab) is the most important antibody value in celiac diagnostics. This antibody targets the enzyme tissue transglutaminase, which is located in the small intestinal mucosa. The discovery that the antibody targets this endogenous enzyme provided proof that celiac disease is an autoimmune disease. 

At the beginning of the 2000s, another antibody test was developed. This involves deamidated gliadin peptide antibodies, often abbreviated as DGP gliadin antibodies. Here, the antibodies target gluten fragments after they have been chemically modified—namely deamidated—by the enzyme tissue transglutaminase. Antibodies against these modified gliadin chains are more specific to celiac disease than antibodies against unaltered gliadin, but they are less informative than transglutaminase antibodies. They only play a role in diagnostics in certain situations. Nevertheless, they are often routinely measured by many doctors and laboratories. This causes unnecessary costs without additional benefit.