Yes, antibodies bind with specific antigens in the antigen-antibody response. Antibodies are proteins produced by the body’s immune system when it detects a foreign substance, known as an antigen. The antigen-antibody response is a process by which the body’s immune system recognizes and responds to antigens, often resulting in the production of antibodies that bind to and neutralize the antigen.
Antigen-antibody interaction, or antigen-antibody reactionis a specific chemical interaction between antibodies made by B cells of White blood cells and antigens during immune reaction. Antigens and antibodies combine by a process called agglutination. It is the fundamental reaction in the body by which the body is protected from complex foreign molecules such as pathogens and their chemical toxins. In blood, antigens are specifically and with high affinity bound by antibodies to form an antigen-antibody complex. The immune complex is then transported to cellular systems where it can be destroyed or deactivated.
The first correct description of the antigen-antibody reaction was given by Richard J. Goldberg in University of Wisconsin in 1952. It became known as “Goldberg’s theory” (of the antigen-antibody reaction).
There are several types of antibodies and antigens, and each antibody is only able to bind to a specific antigen. Binding specificity is due to the specific chemical makeup of each antibody. The antigenic determinant or epitope is recognized by the paratope of the antibody, located in the variable region of the polypeptide chain. The variable region, in turn, has hypervariable regions that are unique amino acid sequences on each antibody. Antigens bind to antibodies through weak, non-covalent interactions, such as electrostatic interactions, hydrogen bonds, Van der Waals forcesand hydrophobic interactions.
The principles of specificity and cross-reactivity of antigen-antibody interaction are useful in the clinical laboratory for diagnostic purposes. A basic application is the determination of the ABO blood group. It is also used as a molecular technique for infection by different pathogens such as HIV, microbes and helminth parasites.
The immunity developed when an individual is exposed to antigens is called adaptive or acquired immunity, in contrast to the immunity developed at birth, which is innate immunity. Acquired immunity depends on the interaction between antigens and a group of proteins called antibodies produced by blood B cells. There are many antibodies and each one is specific to a certain type of antigen. Thus, the immune response in acquired immunity is due to the precise binding of antigens to antibodies. Only a very small area of antigens and antibody molecules actually interact through complementary binding sites, called epitopes on antigens and paratopes on antibodies.
In an antibody, the Fab region (fragment, antigen binding) is formed from the amino-terminal end of the light and heavy chains of immunoglobulin polypeptide. This region, called the variable domain (V), is composed of sequences of amino acids that define each type of antibody and its binding affinity to an antigen. The combined sequence of variable light chain (VI) and variable heavy chain (VH) creates three hypervariable regions (HV1, HV2, and HV3). In VI these are approximately from residues 28 to 35, from 49 to 59 and from 92 to 103, respectively. HV3 is the most variable part. Thus, these regions may form part of a paratope, the part of an antibody that recognizes and binds to an antigen. The rest of the V region between the hypervariable regions are called framework regions. Each V domain has four framework domains, namely FR1, FR2, FR3 and FR4.
Structure of chicken egg lysozyme antigen (HEL). (A) The 3-D structure of HEL (CPK representation) together with three Abs (strand representation). (B) The structure of HEL stained according to the same three epitopes as in (A). (C) The structure of HEL stained according to the epitopes predicted by Discotope (light blue), ellipro (purple), and seppa (pink).
Chemical basis of antigen-antibody interaction
Antibodies bind to antigens through weak chemical interactions, and binding is essentially non-covalent. electrostatic interactions, hydrogen bonds, van der waals forcesand hydrophobic interactions are all known to be involved, depending on where they interact. Non-covalent bonds between antibody and antigen can also be mediated by interfacial water molecules. These indirect links may contribute to the phenomenon of cross-reactivity, that is, the recognition of different but related antigens by a single antibody.
Affinity of the interaction
Antigen and antibody interact through high-affinity binding much like a lock and key. There is a dynamic balance to the connection. For example, the reaction is reversible and can be expressed as:
antibody concentration and [Ag] it’s the antigen concentration, be free ([Ab],[Ag]) or linked ([AbAg]) State.
The equilibrium association constant can therefore be represented as:
Where k it’s the equilibrium constant.
Conversely, the dissociation constant will be:
However, these equations are only applicable to a single epitope binding, i.e. an antigen on an antibody. Since the antibody necessarily has two paratopes and, in many circumstances, complex binding occurs, the multibinding equilibrium can be summarized as:
where, at equilibrium, c is the concentration of free ligand, r represents the ratio of the concentration of bound ligand to the total antibody concentration, and n is the maximum number of binding sites per antibody molecule (the antibody valency).
The total strength of binding of an antibody to an antigen is called its greed for that antigen. Since antibodies are either bivalent or polyvalent, this is the sum of the strengths of individual antibody-antigen interactions. The strength of an individual interaction between a single binding site on an antibody and its target epitope is called the affinity of that interaction.
Greed and affinity can be judged by the dissociation constant by the interactions they describe. The smaller the dissociation constant, the greater the avidity or affinity and the stronger the interaction.
Normally, antibodies can detect and differentiate between molecules outside the body and those produced inside the body as a result of cellular activities. Own molecules as ignored by the immune system. However, under certain conditions, antibodies recognize self molecules as antigens and trigger unexpected immune responses. This results in different autoimmune diseases depending on the type of antigens and antibodies involved. Such conditions are always harmful and sometimes deadly. The exact nature of the antibody-antigen interaction in autoimmune disease is not yet understood.
Antigen-antibody interaction is used in laboratory techniques for serological testing of blood compatibility and various pathogenic infections. The most basic is the determination of the ABO blood group, which is useful for blood transfusion. Sophisticated applications include ELISAenzyme-linked immunospot (Elispot), immunofluorescence and immunoelectrophoresis.
Soluble antigens combine with soluble antibodies in the presence of an electrolyte at the proper temperature and pH to form an insoluble visible complex. This is called a precipitation reaction. It is used for qualitative and quantitative determination of antigen and antibody. It involves the reaction of soluble antigen with soluble antibodies to form a large compounded mesh called a lattice. It occurs in two distinct phases. First, the antigen and antibody rapidly form antigen-antibody complexes within seconds and this is followed by a slower reaction in which the antibody-antigen complexes form networks that precipitate out of solution.
A special ring test is useful for diagnosing anthrax and determining adulteration in food.
It operates in the antigen-antibody reaction in which antibodies cross-link particulate antigens resulting in visible agglomeration of the particle. There are two types, namely active and passive agglutination. They are used in blood tests to diagnose enteric fever.
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