Question

3. What is the optimal ratio of antigen to antibodies for a precipitation reaction to work? 4.) What technique is used to help ensure the optimal ratio? Agglutination Reactions 1. An agglutination reaction requires an antigen to be soluble or insoluble or both? Solulole 2. How is the serum adjusted in a direct agglutination test to identify the reaction between the antibody and antigen?

Answer 1

3) The optimal ratio for antigen to antibodies for a precipitation reaction to work is 1:1.When the antibodies and antigens are in proper ratio, precipitation reactions normally occur. When there is excess amount of either of two, no visible precipitate is formed.

4) One of immunodiffusion test is Ouchterlony double diffusion test can be used to determine optimal ratio of antigen to antibodies. e Ouchterlony double diffusion (ODD) technique is one of the simplest techniques extensively used to check antisera for the presence of antibodies for a particular Ag and to determine its titre.

The method is called "double" referring to the fact that in this procedure, antigen and antibody are allowed to migrate towards each other in a gel and a line of precipitation is formed between the wells where after diffusion optimal ratio of antigen-antibody is formed.

1) In agglutination reaction, antigens need to be soluble to adhere to particles and form visible aggregates.

2)  Direct agglutination is carried out in plastic microtiter plates that have several small shallow wells.Each well contains an equal amount of par­ticulate antigen (e.g. RBCs) but the amount of antibodies in the serum is serially diluted in suc­cessive wells so that their concentration may be half of the previous well.

In a positive reaction, agglutination occurs, and sufficient antibodies are present in the serum to link the antigen together. This results in formation of antibody-antigen mat. However, in the negative reaction, agglutination does not occur and insufficient antibodies are present to cause the linking of antigens.

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