Now, more than ever, timelydetection and prevention of infectious diseases. This requires high-quality and fast diagnostic methods. Traditionally, the clinic uses serological methods to determine the severity of the process and the fact of transferred viral, bacterial and fungal diseases. But these tests do not have enough sensitivity to distinguish between primary infection, reinfection and exacerbation. Therefore, modern scientists have proposed a method for determining the avidity of IgG antibodies.
Avidity: what does it mean?
Различают понятия аффинности и авидности.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 bond strength between the antigen and the antibody. These concepts are directly dependent on each other. The more antigen permanent fragments, the stronger the connection. Allocate low and high avidity.
What does high avidity mean? Let's figure it out.When antigens first enter the body, they stimulate B cells that produce immunoglobulins. At first it is IgM, but then they are replaced by IgG. After the first contact, the affinity, and, consequently, avidity, is low, since the protective mechanisms of the body only adapt to the new pathogen. Seven weeks later, the IgGs "mature", become highly specific, and therefore receive high avidity. And now, in the event of re-infection, the immune system will be ready to quickly respond to the threat.
Avidity index
The level of avidity depends inversely on the dose of 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 the pathophysiologists and immunologists are faced withsuch a phenomenon as reduced immunity with age. Thought and brought a certain ratio, called the avidity index. What does avidity index mean? This number shows the activity of immunoglobulins in relation to the binding of antigens. The index between 15 and 50 percent indicates a primary infection, if the value exceeds 50 percent, then the patient has already suffered from this disease.
Rubella
Rubella virus is extremely negativeinfluence on the fetus, so it is important to determine whether the expectant mother was ill with this disease, or whether she should be vaccinated before pregnancy. For the diagnosis using serological reactions to the affinity of antibodies to antigens. If the immunoglobulins are almost completely bound to the virus particles, then the antibody avidity is high. This may indicate both the transferred infection and good immunity after vaccination.
Sometimes, due to stimulation of lymphocyte clonesrubella virus, registered false positive reaction for class M immunoglobulins. In addition, this result can be observed in those patients in whose blood rheumatoid factor is elevated. Only there is the presence of antibodies that have low avidity. What does it mean? This can be considered confirmation of primary rubella virus infection. In obstetrics, this is a direct indication for abortion.
Toxoplasmosis
As a rule, this infection is hidden andmanifestation of clinical symptoms in case of acquired pathology (for example, such as an enlarged lymph nodes) has a low diagnostic value when it is necessary to find out how long a person has been ill. Determining the avidity of IgG antibodies is a highly specific and sensitive method for diagnosing 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 availableserological analysis to determine the severity of the process was the detection of class M immunoglobulins and an increase in IgG titer. If during the week the number of immunoglobulins G increased four or more times, then this indirectly indicated the progression of the disease.
Even with serological testsIt is difficult for a doctor to determine exactly when a person became infected, since immunoglobulins of classes M and G can persist in the blood for quite a long time. Therefore, the only reliable way to determine avidity. What does it mean? The lower affinity and, accordingly, avidity, the earlier Toxoplasma has entered the body. In addition, a method has recently been discovered for separating low-affinity and high-affinity antibodies for easier counting and determination of the type of infection.
Herpes simplex virus
Большинство людей на планете заражены вирусом herpes simplex Someone with the disease proceeds in a latent form, but most of the symptoms are observed, even if they are minor. 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 an atypical antibody production, it can remain in the human body for the rest of its life, giving false positive and false negative results. False negatives are determined when immunoglobulins are not formed at all or are found in serum in trace amounts. False positive results occur due to the prolonged circulation of antibodies, regardless of the connection with the infection.
In addition, he has cross-reactingantigens that mimic both histocompatibility antigens of normal tissues of the body, and other forms of the herpes virus. Another false positive reaction is determined by the secondary infection of the human immunodeficiency virus.
Cytomegalovirus infection
This virus is the most frequent culprit.termination of pregnancy in the early period. The risk of infection depends on the level of antibodies in the mother at the time of conception. If the initial infection occurred in the first trimester, then the chance of transmission is 50 percent.
What does cytomegalovirus avidity mean?As in all other cases, the determination of the affinity of IgG with a positive reaction to IgM allows you to accurately confirm or deny the presence of a primary cytomegalovirus infection. In addition, it avoids painful and expensive procedures for the expectant mother.
Viral Hepatitis C
The diagnosis of hepatitis is based on the definitionspecific markers that indicate the development of an infectious process. At the same time IgM can appear much later, than IgG, or along with them. This makes it difficult to determine the onset of the disease and the time of primary infection.
The only reliable serological analysisis seroversion and IgG avidity. What does it mean? If the avidity index is low, this is a direct confirmation of the primary infection. In the case of determining the high avidity of IgG class antibodies, we can confidently speak of chronic or postponed hepatitis.
