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Immunology 2011.  The interaction between antigen and antibody  ag - ab reaction  Antigen-antibody reaction is characterized by following salient features.

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Presentation on theme: "Immunology 2011.  The interaction between antigen and antibody  ag - ab reaction  Antigen-antibody reaction is characterized by following salient features."— Presentation transcript:

1 Immunology 2011

2  The interaction between antigen and antibody  ag - ab reaction  Antigen-antibody reaction is characterized by following salient features. 1. Immune Complex 2. Specificity of Ag-Ab Reaction 3. Binding Sties of Antigen and Antibody 4. Binding Forces of Antigen and Antibody 5. Avidity 6. Bonus Effect 7. Cross Reaction

3  When antigen and antibody are brought together, the antibody binds with the antigen to form a complex molecule called immune complex or antigen- antibody complex  Ag + Ab Ag-Ab complex

4  Specificity refers to the discriminate ability of particular antibody to combine with only one type of antigen.  An antibody will combine with the antigen which is the cause for its production.

5  Epitope (antigenic determinant)- The part of the antigen which combines with the antibody.  Paratope (antigen binding site) - The Part of the antibody which combines with the antigen.

6  Binding between antigen and antibody is due to three factors namely, 1. Closeness between antigen and antibody 2. Intermolecular forces 3. Affinity of antibody

7  Avidity refers to the capacity of an antiserum containing various antibodies to combine with the whole antigen that stimulated the production of antibodies.  Avidity is used to denote the overall capacity of antibodies to combine with multivalent antigen

8  the antibody not only binds with the antigen but also the antigens are bridged by a single antibody.  In some cases two antigens may be bridged by a single antibody.  Such a binding is weak.  But when two antigens are bridge by two antibodies, the binding will be strong.  This phenomenon of giving extra- strength to the antigen-antibody complex by the binding of two antibodies to two antigen molecules is called bonus effect.

9  An antiserum raised against a given antigen may sometimes react with another closely related antigen - cross reaction  the antigen which produces the cross reaction is called cross reactive antigen.  The cross reaction is due to the presence of one or more identical antigenic determinants on the related antigen.

10 1.Precipitation 2.Agglutination 3.Cytolysis 4.Complement fixation 5.Flocculation 6.Opsonization 7.Immunoflurorescence

11  reaction between a soluble antigen and its antibody resulting in the formation of insoluble precipitate.  The antibody - precipitin.  due to the formation of Antigen-antibody complex.  The antigen is multivalent and the antibody is bivalent.

12  As each antibody is a bivalent molecule, it can bridge two multivalent antigen molecule.  This bridging leads to the formation of a lattice which forms the precipitate.  When antigen and antibody are in optimal concentration the precipitation is complete and a large lattice is formed.

13  reaction where the antibody of serum causes the cellular antigens to adhere to one another to form clumps.  Antibodies - agglutinins  antigens – agglutinogens  When red blood cells are agglutinated, the reaction - haemagglutination.  bacterial agglutinations

14  is the dissolution of a cell.  RBC is lysed - haemolysis.  bacterial cell - bacteriolysis. Mechanism of Cytolysis:  the antigen-antibody complex activates the complement.  complement binds to the surface antigen of microbe or cell.  The compliment fixed on the surface of the cell causes the disruption of the lipid bilayer of the membrane of the microbe.  As a result, a hole is made on the microbe.  Through this hole the content of the cell are released and the cell is lysed.

15  The binding of complement to antigen – antibody complex is called complement fixation.  When complement is added to a serum containing an antigen and its antibody, the complement is activated and  immediately it binds to the Antigen-antibody complex and the complement is said to be fixed.

16  antigen- antibody reaction brought about by exotoxin and antitoxin.  reaction produces flocculates which do not sediment but remain dispersed in the medium.  Flocculation is somewhat like precipitation, but the precipitates will not sediment.

17  Process by which a particular antigen becomes more susceptible to phagocytosis by combination with an opsonin.  Opsonin is an antibody  when combines with a particulate antigen, increases the susceptibility of the antigen to phagocytosis  In Opsonization - the antibody combines with the surface antigen of bacteria. 

18  This antigen-antibody complex activates complement system.  The activated complement is attached to the antigen- antibody complex to form an antigen-antibody complement complex.  the antigen-antibody-complement is adhered to the phagocytic cells.  The microbe ( antigen) fixed on the phagocytic cell is killed by phagocytosis or lysis.

19  When antibodies are mixed with fluorescent dyes such as fluorescein or rhodamine, they emit radiation.  Phenomenon of emitting radiation by antibodies labeled with fluorescent dye- immunofluorescence.  The immunofluorescence can be observed by a fluorescent microscope.  Application of Immunofluorescence  It is used to locate and identify antigen in tissues.  Certain pathogenic bacteria can be identified.  Antibodies directed to cell or tissue antigen can be detected.

20 Direct method  the antibody labeled with fluorescent dye is applied directly on the tissue section.  The labeled antibody binds with specific antigen.  This can be observed under the fluorescent microscopic.  rabies can be diagnosed.

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