Antigen Antibody Reactions

• Antigen:A toxin or any foreign substance which induces an immune response in the body, especially the production of antibodies.

Antibodies:An antibody (Ab)is a protein produced mainly by plasma cells that is used by the immune system to identify and neutralize pathogens such as bacteria and viruses etc.

INTRODUCTION:

• The antigens and the antibodies combine specifically with each other. This interaction between them is called Antigen-Antibody reaction.

• It may be abbreviated as Ag – Ab reaction.

• These form the basis for immunity

•Reactions observed in Blood banking

• When Ag – Ab reactions occur in vitro, they are known as serological reactions.

• The reactions between Ag and Ab occur in three stages. In first stage the reaction involves formation of

Ag-Ab complex. Sensitization.

The second stage leads to visible events like precipitation, “agglutination .

The third stage includes destruction of Ag or its neutralization “Hemolysis.

Binding Site of Antigen – Antibody Reaction:• In antigen - antibody reaction, the antibody attaches with the antigen.

• The part of antigen which combines with antibody is called Epitope.

• An epitope, also known as antigenic determinant, is the part of an antigen

•The part of an antibody that recognizes the epitope is called a paratope.

Agglutination & Haemolysis

Agglutination is the formation of aggregates of particles, e.g. Red blood cells that bear antigenic determinants (epitope) on their surface and combine with the antibodies present in the test serum.Can observed (ABO grouping) and indirect techniques (antiglobulin procedures). :

Agglutination occurs in two stages

• Sensitization • Zeta Potential

Antigen and Antibody to Show Epitope And Paratope

Agglutination occurs in two stages:

Sensitization:

The antibody attaches itself specifically to the polysaccharide/lipid/protein complexes that form the antigen sites on the red cell.

Requires proper temperature,

ph and ionic Strength of the medium and antigenantibody Ratio.

Clump formation:

• The second phase is the physical process of Agglutination, in which cells come together

• To form clumps. This depends upon the type of antibody involved, the antigen sites available and the zeta‘ potential of the medium in which the cells are suspended.

Zeta Potential:

• Red cells, when in a suspension, carry a negative charge on their surface These charges serve to repel the adjacent cells to avoid sledging. When the cells are suspended in an electrolyte solution,This determines the effective charge of the red blood cells and is designated as the zeta potential.

Zeta Potential:

• In order to bring an antibody close to the surface of the cell, this potential has to be reduced. Even those antibodies that do not exhibit agglutination normally can do so if this potential is reduced.

Proteolytic Enzymes

• The enzymes that are used to enhance antigen-antibodyreactions include papain, ficin and bromelin.

• They also remove structures on the red cells membranes, so as to facilitate the interaction of the antibody with the corresponding antigen. The red cell antigens that are enhanced by enzymes include Rh,Kell, Kidd & Lewis blood groups. Certain red cell antigens, including Duffy (Fy) and M, N,S destroyed by enzymes.

Albumin:

• It is prepared from bovine sources and is commercially available as a 22%

• preparation. Over time, the use of albumin has been abandoned by many blood banks,due to the availability of better potentiators like LISS and Polyethylene Glycol.

LISS

Low-Ionic Strength Saline is widely used in blood banks as an enhancing medium. The incubation time is shortened to 10 minutes and most antibodies are well detected by this technique..PEG (Polyethylene Glycol): It potentiates agglutination by taking out water in hydration, thus binding the cells together and enhancing second-stage agglutination.

Assignment

• Reading & Interpreting agglutination Reactions and Hemolysis

Haemolysis:

This is an important antigen-antibody reaction that results in the lysis of cells. Free haemoglobin‘s red colour is an important end point of an antigen-antibody reaction. Haemolysis is a positive result that indicates the presence of a complement activating antibody. A haemolytic reactionoccurs in two stages:1. The antibody combines with the antigen, thus sensitizing the red cell.2. Sensitized red cells lyse with the help of activated complement components.

The chief use of antigen-antibody reactions are:

• Determination of blood groups for transfusion.• Serological exposure to infectious agents.• Development of immunoassays for the quantification of various substances.• To detect the presence or absence of protein in serum.• Determining the characteristics of certain immuno-deficiency disease.

Application of Antigen – Antibody Reaction:

Conclusion:

we conclude up this topic with a quick review about Antigen – Antibody Reaction.

The antigens and the antibodies combine specifically with each other. This interaction between them is called Antigen-Antibody reaction.

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