Precipitation is serological reaction, which consists in the interaction of soluble antigen to antibody followed by deposition of fine sediment deposition (precipitate).
The reaction of precipitation allows to determine in the studied material the presence of an unknown antigen by adding known antibodies or by means of known antigen is unknown antibody. Precipitation is worse in the absence of salts. Optimum precipitation is in the range of pH of 7.0 to 7.4.
The mechanism of precipitation is close to the mechanism of agglutination. Under the influence of immune serum, reacted to the antigen, decreases the degree of dispersion. It is necessary that the serum and antigen were completely transparent. When setting precipitation can one serum dilution add different cultivation antigen or Vice versa.
Precipitation is logged better if the antigen layering in vitro on the antibody. While seeing the emergence of a precipitate in the form of a ring - colcapitical. Colcapitical carried out in special test tubes with a diameter of 2.5-3.5 mm To determine the number of antigens in the studied material or different antibodies in the serum using the reaction of precipitation in agar: 1% clarified agar poured into a Petri dishes or on the glass. In different holes made in the plate, pour the solution of the antigen and the antibodies, which penetrate towards each other, forming a line of precipitation. The reaction of precipitation is widely used in the diagnosis of anthrax (see Ascoli reaction).
Precipitation in agar allows you to define toxigenicity diphtheria cultures.
In forensic precipitation is used for species identification of blood, organs and tissues using specific precipitating sera.

The precipitation reaction deposition complex antigen (precipition) and antibodies (precipitin). Precipitation is one of the immunological phenomena, allowing to determine the content of antibodies (see) in the serum of patients vaccinated or people, as well as in the blood of immunized animals. When using the standard sera reaction precipitation can be used for titration of different origin soluble antigens (see).
In the most simple form of registration of precipitation reaction to a number of test tubes with a constant amount of antigen add otslaivanie investigated serum in the series fold dilutions. After 30 to 60 minutes incubation at room temperature at the boundary of two liquids formed a ring of turbidity - colcapitical. The minimum number serum, which gives the reaction P., just the title of antisera. In case of return statement reaction with standard anticorodal able to assess the relative concentration of antigen in various biological fluids.
The results of titration of antibodies and antigens on the basis of the above method does not have an absolute quantitative expression. With the aim to quantify the content of antibodies, Heidelberger, Kabat (M Heidelberger, E. Kabat) and others, have developed quantitative method reaction precipitation, which is based on the detection of the so-called zone of equivalence. When mixed age amounts of antigen with constant volume of antisera the number of the formed precipitate initially increases, and then decreases due to the increase of solubility of complex antigen - antibody in excess of antigen. If you define all tubes antibody in the supernatant, it appears that, in the middle tubes of several or even in a single tube of antibodies in the supernatant not; however, here it is the largest of precipitate. Because in the zone of equivalence in the precipitate is also involved all the antigen is introduced into the mixture of reacting substances, after deduction of the amount of protein precipitate protein antigen get the exact size of the content of antibodies in the given volume of the test serum. The protein content of the precipitate after washing chilled Fiziol. solution determine nitrogen or any colorimetric method.
In assessing the values of reaction of precipitation as a diagnostic method, consider that in the immune sera may contain antibodies, not having the properties of precipitin and is, therefore, forming of precipitate by interaction with the antigen. These include first of all incomplete antibodies, as well as some other antibodies belonging to the group of gamma-globulin.
The ability of antisera to precipitate antigen may be impaired by warming up to 65-70°, processing of organic solvents, the recovery in the acidic environment [Isliker (N. Isliker), PRODUCED Kullberg]. The phenomenon of precipitation with anticorodal obviously containing precipitin, is possible only at a certain temperature, the concentration of salts and hydrogen ions. Fastest response P. proceeds at 25-37 degrees. An indispensable condition of education pretipitata - presence in isotonic sodium chloride concentrations of 0.85% NaCl solution). By increasing the concentration of NaCl to 15% of the precipitates formed by polysaccharide antigen nature, partially soluble than you can use to extract pure antibodies. The reaction of precipitation with antigen protein nature runs at the same speed and completeness in 0,85%and 15% solution of NaCl. Optimal for education pretipitata concentration of hydrogen ions corresponds to the pH values from 5.0 to 9.0.
In laboratory practice are used in different modifications reaction precipitation. In particular, the response of thermoreceptor used for the detection of antigens bacteria anthrax, botulism, and others are not exposed to thermal denaturation (Costantini). This reaction is different from the reaction of colcapitical only that as antigen use the filtrate boiled investigated material (see And scale reaction).
In the analysis by using the reaction of precipitation complex mixture of antigens is impossible to characterize the properties of the individual components of the mixture. To solve this problem resort to methods of precipitation of the agar and immunoelectrophoresis. The method of precipitation in the agar in the most common modifications to Ouchterlony (O. Ouchterlony) founded on the fact that the antigen and antisyware, diffundiruet towards each other in a thin layer of gel is formed at a meeting lines P. the number of such lines can be judged on the number of components in the mixture of antigens. Method to Ofgermany lets you compare different antigenic mixture and to determine the degree of kinship present in components. When antigenic analysis of complex mixtures containing substances with the same velocity diffusion into agar, much help can bring method immunoelectrophoresis. The mixture of antigens pre-share in the electric field in the agar plate, and then show the individual components of anticorodal. Antiaborto contribute to rovik done in agar parallel to the line along which moved during electrophoresis antigens. Each antigen network with anticorodal individual arc P. Immunoelectrophoresis is widely used for analysis of abnormalities in the serum proteins, and immunological analysis of tissue and bacterial antigens.
Precipitation in the forensic against. Precipitation is used in forensic medicine for species identification of blood, parts of organs and tissues. In a number of investigation files you want to install species of blood found at the crime instruments, the clothes of the perpetrator or the victim, etc. For the reaction of precipitation used precipitating serum obtained immunization rabbits, roosters, goats proteins different animals. Usually produce serum, precipitating human protein, horses, cats, chickens, pigs, dogs, cattle. They must have a title is not lower than 1:10 000, and to be quite specific. From the study of brown spots or blood prepared drawing on Fiziol. the solution, which undergo precipitating sera. Type of protein is established, if one of the precipitating sera forms a precipitate with the extract of the studied blood at an appropriate control of the reaction. The reaction of precipitation is also possible to set the type of protein tissues and organs of human or animal. Usually the reaction of precipitation produced in test tubes with conical end. When getting muddy extracts the reaction of precipitation produced in agar on Ochterlony.