What is the index of avidity of IgG antibodies to cytomegalovirus and how it is determined

Avidity is the strength of the connection of the antigen and antibody. Determination of avidity is used in the diagnosis of certain infectious diseases, including cytomegalovirus infection.

Fundamentals of immunological interactions

In order to explain the value of this parameter, you need to make a small excursion into the field of clinical immunology.

One of the main ways the immunological defense of the body is realized in the form of an attack by antibodies of the host caught outside antigens.

An antigen is a substance that has the genetic characteristics of alien. It may be, for example, a fragment of bacterial wall or capsule of the virus.

Antibody is a protein that is produced inside the immune cells and may neutralize the antigen.

Scientists distinguish five main classes of antibodies (immunoglobulins). For the diagnosis of cytomegalovirus defeat the most important two of them: IgG and IgM.

IgM antibodies appear in the blood first. Their detection in the blood stream is a symptom of acute infection. As remission of inflammation this kind of immunologically active proteins disappears from the bloodstream.

Representatives of the class IgG in the acute phase of infectious invasion appear later than IgM. However, after infection, they remain in the blood forever, by participating in the formation of immunological memory.

Analyzing the available combinations of blood types of immunoglobulins, it is possible to understand whether a person endures an acute cytomegalovirus infection now, or he was sick before.

If the blood test revealed immunoglobulins IgG and IgM are not detected, it is clear that the patient had previously been ill with cytomegalovirus infection, but is healthy now.

Detection in the bloodstream of both types of antibodies indicates an acute infectious disease or activation of a chronic infectious process.

Why to determine the avidity

It would seem that with the definition phase of the disease all clear. Why, then, need to identify avidity to cytomegalovirus?

The fact that the timing of the finding of antibodies of class IgM in the bloodstream can be very different. It is considered that IgM circulate in the bloodstream for 3-5 months, then disappear. But there are cases when they determined, and after 2 years after the illness. At the same time in severe immunodeficiency, they generally may not be present in the blood. In such situations, it is possible to obtain false positives or false negatives.

Determination of the avidity allows to circumvent this problem and obtain more accurate data regarding carriers of cytomegalovirus. This method introduced into clinical practice in 1989, Professor, University of Helsinki Klaus Hedman.

The importance of the study whenpregnancy

Most often the need for this analysis occurs in pregnant women. This is due to the fact that acute cytomegalovirus lesion may cause significant harm to the developing in utero mother to child.

If a pregnant woman found in addition to IgG antibodies of class M to cytomegalovirus, there is a serious risk. It is extremely important to understand whether this result is a false positive. If it is not, it needs to be clarified, developed an acute infection or reactivation occurred chronic. Depends on the prognosis of gestation. Determination of avidity can clarify the situation.