The antiglobuline is a Anticorps directed against a Immunoglobuline. Used as reagent used in laboratory, it makes it possible to highlight a Anticorps. Analysis allowing this description named at the origin reaction of Coombs is now called test with the antiglobuline .
History and sourceThis test was developed by Robin Coombs, Arthur Dying and Rob Race.
We obtain this reagent antiglobuline by immunization of an animal, a rabbit for example, by a human serum. This human serum contains Immunoglobuline S. For the animal, these immunoglobulins are antigenic, and this rabbit will synthesize anti rabbit antibodies human immunoglobulins . We then obtained an anti rabbit serum immunoglobulin-human , known as human serum A.G.H. or antiglobuline. This antiglobuline, of animal origin, thus sets specifically at the isotypic épitope S of human immunoglobulins.
This test allowed, the origin by technique of agglutination, to highlight the human presence of immunoglobulins fixed on the érythrocyte S.
This reagent could be developed thereafter to recognize spécifiquemet a class of immunoglobulins, IgG, IgA, IgM, or fractions of the Complement, C4, C3b and C3d in particular, likely to be fixed on the érythrocytes. We use either a polyspecific A.G.H (anti-IgG + C3d) - for a tracking of antibody, or of the specific antiglobulines - for a haemolytic diagnosis of anemia, for example.
Direct test with the antiglobuline
The direct test with the antiglobuline (in France T.D.A. or direct reaction of Commbs - R.C.D., in Belgium: Direct Coombs) in the past called direct reaction of Coombs, which makes it possible to highlight the presence of antibodies fixed on the érythrocytes. This test is thus used for the diagnosis of the haemolytic Maladie of the newborn, and in the diagnosis of the autoimmune haemolytic anemias, or of the transfusional incompatibilities.
In these cases the érythrocytes are already covered by human antibodies which are insufficient to cause agglutination alone. These érythocytes is called sensitized red globules (in France G.R.S.). These red globules must be " lavés" , i.e. removed from the plasma surrounding them, and suspended in a saline solution not containing more not fixed antibodies which would neutralize the antiglobuline, - this stage of washing can be now avoided by a technique of filtration on freezing. The addition of the antiglobuline to these sensitized red globules and " lavés" cause agglutination then. The reaction is then positive. This test is also used to check if there were fixing in vivo (in the organization) of the complement, which causes the Hémolyse red globule, or to determine the classes of the immunoglobulin molecules fixed on the studied red globules.
This test must often be supplemented by a technique of elution, sometimes more significant, which also makes it possible to highlight an antibody fixed on red blood corpuscles. In particular for the description of an incompatibility fœto-nursery school ABO, or a recent transfusional incompatibility.
Indirect test with the antiglobuline
The indirect test with the antiglobuline (in France T.I.A. or indirect reaction of Commbs - R.C.I., in Belgium Coombs indirect) in the past called indirect reaction of Coombs , which makes it possible to highlight a irregular antibody nonagglutinant in a serum or an antigen of Blood group on érythrocytes.
Description of an antibody
In the first case it is about a search for irregular agglutinin (in France R.A.I.). The setting in the presence of an unknown serum and of érythrocytes carrying known antigens allows the fixing of the antibodies sought on these érythrocytes and to sensitize them. In the second time, the action of the antiglobuline will allow the description of this possible sensitizing. If the reaction is positive, they is that antibodies were fixed on these érythrocytes, and were thus present in the serum object of the search for irregular agglutinin.
This same test is also used to carry out the test of compatibility (cross-country race matching, englais some), which consists in testing the serum of the patient with a sample of the érythrocytes of the concentrate érythrocytaire that one plans to transfuse. If the reaction is positive, it is that there exists an antibody with respect to the globules of the donor, and that the transfusion considered is incompatible, without one knowing which system of blood group is in question. Another unit of blood will have to thus be selected, and, of course, tested.
Description of an antigen
In the second case, the setting in the presence of a known antibody, it acts then of a serum test, with unknown érythrocytes allows the description of the antigen corresponding on these érythrocytes. It is about the determination of a phenotype of blood group.
Since this test spread and allows to highlight an immunoglobulin human in very liquid or specifically fixed on any support. Either by techniques using of the red globules sensitized like revealing, techniques of inhibition or consumption of antiglobuline used for the determination of the group Gm, km, ISf, Am, or by a antiglobuline marked, which makes it possible to detect its presence, i.e. its specific fixing on human immunoglobulins.
Groups Am, Gm, ISf, kmThe human anti-D antibodies (inevitably for several reasons), of a subject of group Gm (1,17,21) are fixed on a red globule Rh+, D. We have sensitized red globules then, GRS, but which are not bound, the antione being an incomplete antibody. We make act on these GRS anti-globuline anti Gm1 (antiglobuline of human origin). We cause an agglutination then.
Let us mix a serum X with this anti Gm1 before making it act on our GRS. If this serum X contains an immunoglobulin of Gm1 group, anti Gm1 will form a complex antigen-antibody, and will be consumed, and thus neutralized. It will not be able to act on our GRS, and the reaction will be negative. We will conclude from it that our serum X is of Gm1 group, because our reaction of agglutination was inhibited.
If our serum X is Gm-1, it will not neutralize our anti-globuline which will be able to then bind to anti-D fixed on our GRS, and to cause agglutination of it. See irregular Antibodies and potential zeta.
This technique of inhibition of agglutination is a very significant technique, a serum diluted with the 1/100e, even more, can inhibit the reaction and made it possible, before molecular biology, to highlight the origin human (or simiesque, we are cousins) of a bloodstain.
Idem for the antiones, Gm17, Gm4, Gm… or anti-Km1… which makes it possible to determine the serum groups of immunoglobulins
Thus, the plate test of Coombs, or test of Dickson, allows thanks to a marked antiglobuline, to highlight the sensitizing of the plates by an antibody, which it is about the Purpura thrombopenic idiopathic, P.T.I or of the Thrombopénie néonatale by Incompatibilité fœto-nursery school.
Parasitic, viral serology…
The antiglobuline can be marked by a Fluorochrome, it then allows by technique of immunofluorescence the description of suppressor antibodies, toxoplasme or Plasmodium in particular. Marked by an enzyme, it is then about a technique of immuno-enzymology which allows the description of antivirus antibody whose specific antigens are fixed on a plastic support (balls or cups), anti-hepatitis, for example. Marked with Radioactive iodine , it enters within the framework of radioimmunology.
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