Soluble antigen is mixed with the corresponding antibody. In the presence of electrolytes, if the ratio of the two is appropriate, a precipitate will appear, which is called Precipitation. Due to the precipitation reaction antigen multi-colloid solution. The precipitate is mainly composed of antibody proteins.
In order to obtain an appropriate ratio of antigen to antibody, to ensure that there are enough antibodies, and the antigen molecule is small and has a large reaction area, the operation is usually to dilute the antigen instead of the antibody.
The types of precipitation reactions include cyclic precipitation, flocculent precipitation, capsule swelling, agar diffusion and immunoelectrophoresis. In addition, there are radioisotope labeling, enzyme labeling and other assays.
Cyclic precipitation reaction
When the antigen and the corresponding antibody form a contact surface, if the ratio of the two is appropriate, a milky white ring can be formed on the contact surface, which is a positive precipitation reaction.
1. Materials
(1) Immune serum: immune rabbit anti-human serum;
(2) Antigen: human serum;
(3) Small precipitation tube, capillary pipette, rubber tip, normal saline.
2. Method
(1) Take 2 small precipitation tubes, suck about 0.2 ml of anti-human serum with a capillary pipette, add it to the first tube, and be careful not to have air bubbles;
(2) Add 0.2 ml of normal saline to the second tube with a capillary pipette;
(3) Dilute 0.2 ml of blood with a capillary pipette and add it to each tube. When adding, care should be taken to make the antigen solution slowly flow down from the tube wall and float on the surface of the serum to form an obvious interface. Do not mix them;
(4) Put it at room temperature for 10-20 minutes, observe whether there is a milky white precipitation ring on the liquid surface, if there is, it is positive.