Precipitation of antigen-antibody combinations in microbiological diagnosis

2021-08-22 10:25 PM

Antigens and antibodies are placed into holes in the agar. They diffuse and form precipitation lines on the agar surface. An artifact containing multiple antigens forms multiple precipitates.

Precipitation of antigen-antibody

Precipitation of antigen-antibody

Principles

A precipitation reaction is a combination of soluble antigens when meeting the corresponding antibody, forming a precipitate that can be observed directly with the naked eye or by looking at it with a magnifying glass.

The polyvalent antigen combines with the divalent antibody to form a 3-D reticular precipitate. The reaction can be carried out in a liquid or gel medium.

Precipitation reaction in liquid medium

Qualitative response

Performed with diluted or undiluted antiserum. Antiserum and antigen were mixed together, and a precipitate was observed. It is also possible to add antiserum into a small test tube and then add the antigen gradually down the wall of the tube. A precipitation ring is observed at the interface plane.

Quantitative response

Allows determination of the amount of antibody that precipitates with a known amount of antigen. Add an increasing amount of antigen to a constant number of antisera, collect the precipitate by centrifugation, and quantify the protein using conventional methods to determine the amount of reacted antibody.

Precipitation reaction in gel medium

Ouchterlony Double diffusion-reaction

Antigens and antibodies are placed into holes in the agar. They diffuse and form precipitation lines on the agar surface. An artifact containing multiple antigens forms multiple precipitates.

Immunological relationships between two antigens can be investigated by a double diffusion reaction. The bands of precipitate formed may indicate immunological similarity, partial homogeneity, or non-relationship.

Single diffusion-reaction

It is possible to make diffusion in gel media more sensitive by mixing antibodies into the agar. Antigen was diffused from a perforated hole in the antibody-containing agar. At the beginning of diffusion, the antigen is still in high concentration, so it forms soluble complexes. With further diffusion, the concentration gradually decreased until a suitable value was reached at which a precipitate ring was formed. This method can not only be used to identify antigens but can also allow the quantification of IgG in serum.