[BIOLOGICAL AND IMMUNOCHEMICAL PROPERTIES OF POLYREACTIVE IMMUNOGLOBULINS].

A previously unknown phenomenon of acquired polyreactivity for serum immunoglobulins, which were subjected either to solutions of KSCN (3.0-5.0 M), low/high pH (pH 2.2-3.0), or heating to 58-60 degrees C, was described by us in 1990 year. Much later, eleven years after that, similar data were published by others, which completely confirmed our results concerning the influence of either chaotropic ions or the drastic shift of pH on immunoglobulins polyreactive properties. Our further investigations of polyreactive serum immunoglobulins (PRIG) properties have shown that the mechanism of non-specific interaction between PRIG and antigens much differs from the mechanism of interaction between specific antibodies and corresponding antigens. Later we have shown that the increasing of PRIG reactivity could be induced in vivo, and PRIG are one of serum components for human or animal sera. Then, it could be suggested that PRIG can perform certain biological functions. Studying of PRIG's effect on the phagocytosis of microbes by peritoneal cells or the tumor growth have shown that PRIG can play a certain role in protecting the body from infections and probably can influence on the development of various pathological processes. Recently we have also found that PRIG IgG contents significantly increases in aged people. These data demonstrate that further investigations of PRIG's immunochemical properties and studying of their biological role in organism protection from various diseases is very intriguing and important.

FUNDAMENTAL DIFFERENCES BETWEEN NATURAL ANTIBODIES AND POLYREACTIVE IMMUNOGLOBULINS.

A problem of similarity and differences between so-called polyreactive immunoglobulins (PRIGs) and natural antibodies (NAbs), capable of cross-reacting with some structurally dissimilar antigens, has been considered. The analysis of mechanisms of an unspecific interaction between PRIGs or NAbs and antigens evidences for the fact that essential differences exist between these substances. These differences permit classifying the abovementioned substances as different types of immunoglobulin molecules. The major difference between PRIGs and NAbs may include both the mechanisms of the above mentioned immunoglobulin molecules binding to antigens and their interaction affinity, as well as an absolutely different influence of some low-molecular substances on the efficiency of the interaction with antigens. Relying on the obtained data it can be assumed that, since PRIGs and NAbs have fundamental differences, they may perform not only similar but also different functions of the immune system.

[Interaction peculiarities of polyreactive immunoglobulins and various antigens].

The influence of twin 20, lysozyme and protamine on the capability of polyreactive immunoglobulins (PRIG) to attach to various antigens was investigated. Twin 20 can inhibit the binding of PRIG to antigens on immunological plates but lysozyme and protamine can enhance it. As far as the mixture of the optimal concentrations of lysozyme and protamine cannot increase PRIG-antigen interaction in comparison to the optimal dose of protamine, we have concluded that the mechanism of their effect on PRIG binding is similar. Of special interest is the fact that twin 20 at optimal concentration of lysozyme or protamine does not decrease PRIG binding to various antigens but, on the contrary, increases PRIG-antigen interaction.

Age changes of human serum polyreactive immunoglobulins (PRIG) activity.

It has been determined that activity of serum polyreactive immunoglobulins (PRIG) changes with age in practically healthy people at the age from twenty five to seventy. Therewith, the activity of serum IgG PRIG increases most of all (about 3-4 times), while IgM PRIG activity, on the contrary, does not increase, but sometimes even decreases with age. IgA PRIG activity varies significantly more than IgG PRIG activity and, besides, IgA PRIG significantly less depends on age than IgG PRIG. The age changes in the activity of human serum PRIG, belonging to different types of immunoglobulins, may evidence for the important functional role of these immunoglobulins that has to be clarified.

[New approach in evaluating affinity of bivalent antibodies by the method of surface plasmon resonance. Theory].

Theoretical aspects of the affinity evaluation for the interaction between bivalent receptors (or antibodies) and corresponding ligands (or antigens) are considered. It was shown that the ligand presence in the solution at the stage when the receptor dissociation occurs leads to the increase of the affinity evaluation accuracy. We demonstrated that the analysis of the dissociative curve of the receptor from the chip is not necessary for affinity determination; the analysis of associative curve is sufficient for this purpose. We also suggested a new approach for evaluating the affinity of bivalent receptors (or antibodies) when these reagents are present in the studied solution and the correspondent ligand (or antigen) is immobilized on the chip.

[Avidity of bivalent antibodies. Problems of its experimental determination and theoretical evaluation].

Some problems of experimental determination or theoretical evaluation of antibody avidity are considered. It was shown that in order to determine the fraction of nonoccupied antibodies in their mixture with the excess of the corresponding antigen which is required to estimate avidity the methods should be used which are more sensitive than ELISA. The available methods did not allow determining the avidity of bivalent antibodies because of many reasons. However, in the recent years new methods were suggested that make it possible to evaluate the avidity of bivalent antibodies and that of the receptors which consist of two binding sites connected by a flexible linker of the known length. Thus, there are all possibilities now for determining the avidity of bivalent antibodies in experiments or by theoretical methods.

[Advantages of two- or polyvalent binding of a receptor to the corresponding ligand in comparison to univalent binding].

The features of monovalent and bivalent binding of receptors (or antibodies) with a polyvalent ligand (or with an antigen) are considered. It is shown that the rigid connection of the binding sites of the receptor brings to high increase of binding affinity for the corresponding ligand, but only in case if its epitopes are fully complementary to both sites of the receptor binding. If not, then there is no advantage of the binding of bivalent receptor before univalent binding. If the binding sites of the receptor are connected by a flexible linker, then regardless of location of epitopes of the corresponding ligand there is the successful fastening of receptor and ligand. Exactly the connection by a flexible linker is used by Nature in most cases at constructing of polyvalent receptors.

[The effect of blood serum polyreactive immunoglobulins on serum antibody affinity determination].

The presence of polyreactive immunoglobulins in sera may substantially influence on the accuracy of antibody affinity determination. In order to obtain precise values of antibody affinity one should apply one of two following ways. First, one should block polyreactive immunoglobulins with high concentration of Twin 20 and high concentration of any antigen which does not interact with studying antibody. After this antibody affinity may be determined by traditional methods. Another way is the application of the method suggested by us earlier, which allow determining affinity of two antibodies in a mixture and the relation of their concentrations.

[Relationship between the reaching of equilibrium and the accuracy of the affinity determination for antibody-antigen reaction].

Theoretical investigation of the relationship between the reaching of equilibrium and the accuracy of the affinity determination for antibody-antigen reaction were carried out. It was shown that evaluation of the reagent concentrations before reaching the dynamic equilibrium leads to a decrease of estimation accuracy for the affinity constant of this reaction. We have established that for most of typical antibodies the dynamic equilibrium of their reaction with corresponding antigens comes 2-4 hours after the beginning.

[Shortcomings of traditional method for determining antibody affinity and their correction].

It was shown that application of the traditional method for antibody affinity determination may give not exact and non complete information about the characteristics of studied antibodies especially if studying specimens contain two or more species of antibodies with different affinity. In order to avoid this problem it is recommended to use another approach, suggested by us earlier. Our approach allows elucidating that studying specimens contain more than one kind of antibodies and this allows applying a proper method for an- tibody affinity evaluation. Such method, which allows determining the affinity of two antibodies in a mixture that have different affinity, is also described.