Serum precipitin test
The serum precipitin test (synonym Uhlenhuth sample ) is a serological proof of relationship based on the precipitation of sera with antigens in the blood serum that are related to the antigen used to produce the immune serum.
The test is based on the specific antigen-antibody reaction to determine the antigenic identity of two organisms with regard to their proteins (synonym proteins). Each species has species-specific proteins and this test can therefore be used to determine their degree of similarity. The antibodies in the serum lead, when they come into contact with antigens, depending on their relationship to the antigen that was used to generate the serum, to a precipitation (synonym for precipitation, precipitation) of the proteins dissolved in the blood serum . The more similar the amino acid sequences of the serum proteins used are, the greater the genetic match, which results in a greater relationship and greater precipitation by the serum. This line of reasoning also applies in reverse. In addition to determining the species of an unknown blood sample, the test was also used for the quantitative analysis of phylogeny and for the detection of admixtures of undeclared animal species in meat and sausage .
The procedure was discovered by Paul Uhlenhuth in 1901. With his method, it was possible for criminology for the first time to reliably differentiate animal and human blood in the presence of traces of blood .
The precipitin test can be used in general for the examination of kinship relationships, in the following it is described for the examination of a relationship to human blood. However, it could also be carried out for other organisms accordingly. First of all, what is known as human serum is required, which is obtained by letting human blood stand for some time in a test tube so that the solid components are deposited in the lower area of the test tube and the remaining liquid ( plasma without fibrinogen ) on top . This serum is injected into a rabbit or other intermediate organism, from which blood is drawn again after a few weeks.
The above procedure for separating the serum from the liquid is carried out with the rabbit blood and a new serum is obtained, the anti-human serum, which contains antibodies against human serum proteins. If this anti-human serum is now mixed with human blood, then there is a precipitation ( precipitation ), since these antigens are immediately fought by antibodies. The maximum achievable precipitation of the antigen-antibody complexes (with 100% identity) is defined as a 100 percent precipitation (as a comparison standard). A sample that is as closely related as possible, carried along as a negative control , does not lead to precipitation because it is not related.
With other living beings there are different results with this anti-human serum, whereby the degree of precipitation allows conclusions to be drawn about the phylogenetic proximity. The more proteins are precipitated by the antibodies contained in the anti-human serum, the more similar the organisms are to humans in terms of proteins. Since the specific proteins of every organism have developed in the course of evolution, a great similarity in relation to the proteins indicates a close relationship between two organisms. However, since the precipitin reaction provides a poorly differentiated result, cannot be used in all animal groups and does not allow more precise conclusions to be drawn as to when the lines of development of two living things separated, it has lost much of its importance today. Instead, a genetic fingerprint is now more likely to be examined with DNA sequencing , amino acid sequence analysis (using Edman degradation ), restriction fragment length polymorphism , STR analysis or with DNA-DNA hybridization .
In the following, the serological relationship test of human serum proteins in relation to humans , chimpanzees , gorillas , orangutans , baboons , cattle , sheep , deer , horses , marsupials , birds and rabbits is carried out as an example . The intermediate organism for obtaining the test serum (here an anti-human serum) is a rabbit.
- It is taken from human blood serum and injected into a rabbit.
- After some time, the rabbit forms antibodies against human proteins (more precisely: against antigenic proteins and carbohydrates ).
- Now blood is taken from the rabbit and test serum is made from it.
- The test serum is added to blood samples from humans, chimpanzees and orangutans.
- The blood in the test serum clumps together (precipitation / precipitation) depending on how strongly the antibodies match the antigens.
- Human: 100%
- Chimpanzee: 85%
- Gorilla: 64%
- Orangutan: 42%
- Baboon: 29%
- Sheep: 18%
- Beef: 10%
- Deer: 7%
- Horse: 2%
- Marsupial: 0%
- Bird: 0%
- Knauer, Bernhard; Kronberg, Inge Dr .; Krull, Hans-Peter (2007): Natura Biology for High Schools - Evolution, Klett Verlag Stuttgart, p. 94f.
- Wright, CA (1966): Experimental Taxonomy: a review of some techniques and their applications. Int. Rev. gen. Exp. Zool. 2, 1-42.
- Wright, CA (Ed., 1974): Biochemical and Immunological Taxonomy of Animals. London & New York. Academic Press.
- Antje Starke, Rolf Wellinghorst: Discovering Biology Today 12 (Saxony), Schroedelverlag.
- Paul Uhlenhuth : A method for differentiating the different types of blood, in particular for the differential diagnostic evidence of human blood. In: German Medical Weekly . 1901, Vol. 27, No. 6, , pp. 82-83; and: More information about my method of detecting human blood. Ibid pp. 260-261.
- Jürgen Thorwald : The hour of the detectives. Becomes and worlds of criminology. Droemer Knaur, Zurich and Munich 1966, pp. 31–35.