Avidiness - what does this mean? Avidity of IgG antibodies to cytomegalovirus: features and interpretation

Now, as never before, the timely detection and prevention of infectious diseases is important. This requires qualitative and rapid methods of diagnosis. Traditionally, the clinic uses serological methods to determine the severity of the process and the fact of the transmitted viral, bacterial and fungal diseases. But these tests do not have enough sensitivity to distinguish between primary infection, reinfection and exacerbation. Therefore, modern scientists proposed a method for determining the avidity of IgG antibodies.

Avidiness: what does this mean?

There are concepts of affinity and avidity. Affinity is a thermodynamic characteristic that quantitatively describes the strength of the interaction of an antibody and an unchanged part of an antigen. In turn, avidity determines the strength of the connection between the antigen and the antibody. These concepts are in direct dependence on each other. The greater the antigen constant fragments, the stronger the connection. Highlight low and high avidity.

What does high avidity mean? Let's understand. When antigens first enter the body, they stimulate B cells that produce immunoglobulins. First it is IgM, but then they are replaced with IgG. After the first contact affinity, and consequently, avidity, is low, since the protective mechanisms of the organism only adapt to the new pathogen. After seven weeks, IgG "mature", become highly specific, and therefore get high avidity. And now, in case of re-infection, the immune system will be ready to respond quickly to the threat.

The index of avidity

The level of avidity is inversely proportional to the dose of the antigen and its nature, as well as the level of mutations in human cells. The lower the initial dose, the higher the affinity, and vice versa.

And then pathophysiologists and immunologists faced with such a phenomenon as a decrease in immunity with age. Thought and derived a certain ratio, called the index of avidity. What is the index of avidity? This number shows the activity of immunoglobulins in relation to antigen binding. The index in the interval between 15 and 50 percent indicates a primary infection, if the value exceeds 50 percent, then the patient was already ill with this disease.

Rubella

The rubella virus has an extremely negative effect on the fetus, so it is important to determine if the mother is ill with this disease, or before the pregnancy, she should be vaccinated. Serologic reactions to the affinity of antibodies to antigens are used for diagnosis. If immunoglobulins are almost completely bound to viral particles, then avidity of antibodies is high. This can indicate both the transferred infection and good immunity after vaccination.

Sometimes, due to the stimulation of clones of lymphocytes by the rubella virus, a false positive reaction is detected for class M immunoglobulins. In addition, such a result can be observed in those patients whose blood rheumatoid factor is elevated . Only there is the presence of antibodies, in which low avidity. What does it mean? This can be considered a confirmation of a primary infection with the rubella virus. In obstetrics, this is a direct indication for the termination of pregnancy.

Toxoplasmosis

As a rule, this infection is hidden, and the manifestation of clinical symptoms in acquired pathology (for example, such as lymph node enlargement) is of low diagnostic value when it is necessary to find out how long a person is sick. Determination of avidity of IgG antibodies is a highly specific and sensitive method of diagnosis of acute primary toxoplasmosis, which is especially important when examining pregnant women to eliminate the potential risk of congenital toxoplasmosis in children.

Until recently, the only available serological analysis to determine the severity of the process was the detection of class M immunoglobulins and an increase in the IgG titer. If within a week the amount of immunoglobulin G increased four or more times, this indirectly indicated the progression of the disease.

Even in the conduct of serological studies, it is difficult for a doctor to determine when a person has become infected, since immunoglobulins of classes M and G can persist for a long time in the blood. Therefore, the only reliable way to determine avidity. What does it mean? The lower the affinity and, accordingly, avidity, the earlier toxoplasma penetrated the body. In addition, a method for separating low-affinity and high-affinity antibodies has recently been discovered for easier counting and determining the type of infection.

Herpes simplex virus

Most people on the planet are infected with the herpes simplex virus. In someone, the disease runs in a latent form, but most symptoms are observed, even if they are insignificant. In addition, there are some difficulties with how to determine the avidity of herpes. What does this mean in practice? This virus is characterized by atypical antibody formation, it can be in the human body for life, give false positive and false negative results. False negatives are determined when immunoglobulins are not formed at all or are in serum in trace amounts. False positive results are due to the prolonged circulation of antibodies regardless of the connection with the infection.

In addition, it has cross-reacting antigens that mimic both histocompatibility antigens of normal body tissues and other forms of the herpes virus. Another false positive reaction is determined by secondary infection with the human immunodeficiency virus.

Cytomegalovirus infection

This virus is the most common culprit for early termination of pregnancy. The risk of infection depends on the level of antibodies in the mother at the time of conception. If the primary infection occurred in the first trimester, then the chance of transmission of infection is 50 percent.

What does avidity mean to cytomegalovirus? As in all other cases, the determination of IgG affinity for a positive response to IgM allows the exact confirmation or denial of the presence of a primary cytomegalovirus infection. In addition, this avoids the painful and costly procedures for a future mother.

Viral hepatitis C

Diagnosis of hepatitis is based on the definition of specific markers, indicating the development of the infectious process. In this case, IgM can appear much later than IgG, or simultaneously with them. This makes it difficult to determine the onset of the disease and the time of primary infection.

The only reliable serological analysis is serocoversion and IgG for avidity. What does it mean? If the index of avidity is low, this is a direct confirmation of the primary infection. In the case of determining the high avidity of IgG antibodies, one can confidently talk about chronic or transferred hepatitis.