What is the Ascoli precipitation experiment like?

Vascoli test (anthrax thermoprecipitation):

Bacillus anthracis polysaccharide antigen can withstand heat and decay, and can still precipitate with the corresponding immune serum (antibody) after long-term boiling for old specimens or decayed cadaveric organ specimens that are not suitable for Bacillus anthracis culture.

It is often used for leather quarantine.

Precipitation reaction. precipitation) is a serological reaction. The soluble antigen binds to the corresponding antibody, and in the presence of an appropriate amount of dielectric, after a certain period of time, it forms a precipitate visible to the naked eye.

The antigen of the precipitation reaction can be polysaccharides, proteins, lipids, etc. Compared with the corresponding antibody, the molecule of the antigen is small, and the amount of antigen contained in the unit volume is large, so when doing quantitative tests, in order not to make the antigen excessive, the antigen should be diluted, and the dilution of the antigen should be used as the titer of the precipitation reaction. It is customary to refer to the antigen involved in the precipitation reaction as the precipitator, and the antibody as the precipitin.

The experimental methods of precipitation reaction can be roughly divided into three basic types: ring method, flocculent method and agar diffusion method.

The cyclic precipitation reaction is also known as the cyclic test. It is mainly used for qualitative testing of antigens. Unknown antigens are detected with known antibodies.

A known antiserum is added to a small-bore tube, and then the antigen to be tested is carefully added to the surface of the serum to create two layers with a clear interface. A few minutes later, a white precipitate ring appears at the junction of the two interfaces, which is positive. This test is often used for antigen characterization, such as the diagnosis of anthrax (Ascoli's test), the identification of blood stains, and the hemophilia of vector insects.

Flocculation Reaction Antigen and corresponding antibody are mixed in a test tube or on a concave slide, and if there is a flocculent precipitate visible to the naked eye, it is a positive reaction. For example, the Kahntest is used to diagnose syphilis.

Agar diffusion test uses soluble antigens and antibodies to diffuse in semi-solid agar, if the antigen corresponds to the antibody and the ratio is appropriate, a white precipitate line will appear, which is a positive reaction. Agar diffusion tests can be performed in tubes, in plates, and on agar on slides. It can be divided into two categories: one-way agar diffusion test and two-way agar diffusion test.

The one-way agar diffusion test is a commonly used method for the quantitative detection of antigens. Mix an appropriate amount of antibody with agar, pour it into a plate, after solidification, punch a hole in the plate, add antigen to the well, and the antigen will spread around the well, and bind to the antibody in the agar while spreading. After a certain period of time, a white precipitate ring is formed at the appropriate ratio of the two.

The diameter of the precipitating ring is directly proportional to the concentration of the antigen. If a standard curve is made in advance with different concentrations of standard antigen, the amount of antigen in the specimen can be found from the curve. This test is mainly used to detect the content of various immunoglobulins in the specimen and various complement components in the serum, and the sensitivity is very high.

The two-way agar diffusion test is to pour semi-solid agar into a flat dish or a glass slide, and after it solidifies, punch holes in the agar plate, and inject antigens and antibodies into the small holes respectively to diffuse the two. If the antigen and antibody correspond to each other, and the concentration and proportion are appropriate, after a certain period of time, a clearly visible precipitation line will appear between the antigen and antibody pores. The bidirectional agar diffusion method can be used to analyze a variety of antigens in solution.

A pair of antigen and antibody systems can only form one precipitation line, and different antigen and antibody systems can form different precipitation lines in the agar because of the different diffusion rates in the agar. This method is mainly used for the detection of various immunoglobulins, alpha-fetoprotein, hepatitis B surface antigen, etc. in serum. The disadvantage is that it takes too long and the sensitivity is not high.