محاضرة 2_ 2.pdf

‫جامعة تكريت‬ ‫كلية الطب‬ ‫فرع االحياء المجهرية الطبية‬ ‫م‪.‬م‪.‬جعفر جميل ابراهيم‬ ‫المرحلة الثانية‬ ‫‪Antigen – antibody reaction‬‬ ‫‪Lab -2-‬‬ Contents 1. Introduction. 2. Salient Features of Antig...

‫جامعة تكريت‬ ‫كلية الطب‬ ‫فرع االحياء المجهرية الطبية‬ ‫م‪.‬م‪.‬جعفر جميل ابراهيم‬ ‫المرحلة الثانية‬ ‫‪Antigen – antibody reaction‬‬ ‫‪Lab -2-‬‬ Contents 1. Introduction. 2. Salient Features of Antigen - Antibody Reaction. 3. Strength of Antigen - Antibody Reaction. 4. Properties of Antigen - Antibody Reaction. 5. Types of Antigen - Antibody Reaction. 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 humoral immunity or antibody mediated immunity. These reactions form the basis for detection of infectious disease causing agents and also some non- specific Ag's like enzymes. Introduction When Ag- Ab reactions occur invitro, 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. The second stage leads to visible events like precipitation, agglutination etc. The third stage includes destruction of Ag or its neutralization Salient Features of Antigen - Antibody Reaction: Specificity of Antigen - Antibody Reaction. Immune complex. Binding Site of Antigen - Antibody Reaction. Binding Force of Antigen - Antibody Reaction. Specificity Specificity refers to the ability of an individual antibody combining site to react with only one antigenic determinant or the ability population of a of antibody molecules to react with only one antigen. Specificity For example, the antibody produced against lens antigen will react only with lens-antigen. Similarly, the antibody produced against kidney antigen will react with only kidney- antigen. Immune Complex An immune complex is formed from the integral binding of an antibody to a soluble antigen. The bound antigen acting as a specific epitope, bound to an antibody is referred to as a singular immune complex. Immune Complex Mechanisms of antigen-antibody interaction leading to inflammation. Antigen-antibody immune complex formation results in complement activation, Opsonization of target cells, assembly of membrane attack complexes and release of complement activators for chemotaxis. 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 that is recognized by the immune system, specifically by antibodies, B cells, or T cells. The part of an antibody that recognizes the epitope is called a Paratope. Binding Force of Antigen - Antibody Reaction The binding between antigen and antibody in Ag- Ab reaction is due to three factors namely: 1. Closeness between antigen and antibody. 2. Non- covalent bonds or Intermolecular forces. 3. Affinity of antibody. Binding Force of Antigen - Antibody Reaction Closeness between antigen and antibody: When antigen and antibody are closely fit, the strength of binding is great. When they are apart binding strength low. Non Covalent Bonds The bonds that hold the antigen to the antibody combining site are all non- covalent in nature. These include hydrogen bonds, electrostatic bonds, Van der Waals forces and hydrophobic bonds. Affinity of antibody Antibody affinity is the strength of the reaction between a single antigenic determinant and a single combining site on the antibody. Properties of Antigen - Antibody Reaction The properties of antigen and antibody can be explained with the help of three points : * Antibody Affinity. * Antibody Avidity. * Cross reaction. Affinity of Antibody The Interactions between antigen and antibody involve non-covalent binding of an antigenic determinant (epitope) to the variable region (complementarity determining region, CDR) of both the heavy and light immunoglobulin chains. These interactions analogous to those observed in enzyme-substrate interactions and they can be defined similarly. Avidity of Antibody It is the strength of the bond after the formation of Ag - Ab complexes. It is used to denote the overall capacity of antibodies to combine with the multivalent antigen. A multivalent Ag has many types of antigenic determinants. Cross Reaction An antiserum raised against an Ag, can also react with a similar Ag of another type. This is called cross reaction and the Ag which produces the cross reaction is called Cross reactive Ag. But the strength of Ab raised against its own Ag is strong. Types of Antigen - Antibody Reaction The types of antigen - antibody reactions are: Precipitation Reaction. Agglutination Reaction. Complement Fixation. ELISA - Enzyme Linked ImmunoSorbent Assay. Immunofluorescence