Precipitation and Agglutination PDF

 PRECIPITATION - involves combining soluble antigen with soluble antibody to produce insoluble complexes that are visible. AGGLUTINATION - is the process by which particulate antigens such as cells aggregate to form larger complexes when a specific antibody is present.  Affinity - i...

 PRECIPITATION - involves combining soluble antigen with soluble antibody to produce insoluble complexes that are visible. AGGLUTINATION - is the process by which particulate antigens such as cells aggregate to form larger complexes when a specific antibody is present.  Affinity - is the initial force of attraction that exists between a single Fab site on an antibody molecule and a single epitope or determinant site on the corresponding antigen The strength of attraction depends on the specificity of antibody for a particular antigen.  Cross-reactivity - Antibodies are capable of reacting with antigens resembling the original antigen that induced antibody production Avidity - this represents the overall strength of antigen– antibody binding and is the sum of the affinities of all the individual antibody–antigen combining sites The more bonds that form between antigen and antibody, the higher the avidity is  All antigen–antibody binding is reversible and is governed by the law of mass action. This law states that free reactants are in equilibrium with bound reactants. The equilibrium constant K represents the difference in the rates of the forward and reverse reactions according to the following equation:  When the value of K is higher, the amount of antigen–antibody complex is larger and the assay reaction is more visible or easily detectable. The ideal conditions in the clinical laboratory would be to have an antibody with a high affinity, or initial force of attraction, and a high avidity, or strength of binding. The higher the values are for both of these and the more antigen–antibody complexes that are formed, the more sensitive the test.  ZONE OF EQUIVALENCE - the number of multivalent sites of antigen and antibody are approximately equal LATTICE HYPOTHESIS – Postulated by Marrack, based on the assumptions that each antibody molecule must have at least two binding sites and the antigen must be multivalent. PROZONE – Antibody excess POSTZONE – Antigen excess  A false-negative reaction may take place in the prozone because of high antibody concentration. Remedy: Dilute the antibody and repeat the test In the postzone, excess antigen may obscure the presence of a small amount of antibody. Remedy: Repeat test after 1 week with additional sample                         Any questions? Don't hesitate to ask for help