IMMUNOGLOBULINS- ANTIGEN-ANTIBODY REACTIONS
Salient Features of Antigen – Antibody Reaction Agglutination Reaction:• When a particular Ag is mixed with its Ab's in thepresence of. The reaction is specific; an antigen combines only with its homologous antibody and vice versa. The specificity however is not absolute and. Thus, our concept of antigen-antibody reactions is one of a key (i.e. the antigen) the reaction of an antibody with the antigen can be detected by agglutination.
Discard the final 50 ml taken from row 9. Make sure the RBCs stay adequately resuspended as you are using them. Periodically invert the capped tube to keep them resuspended evenly.
Incubate the plate for 24 hours at room temperature. Come back the next day and observe agglutination. Positive wells will exhibit a diffuse and confluent settling of the RBC and Ab, while in negative wells, all cells will roll down to the bottom and it will look more like a dot.
Immunobiology A-7 Study Questions 1. What is the difference between precipitation and agglutination? Which one of these two methods is more sensitive and why?
What type of structure on your red blood cells decides your blood type? You used the slide agglutination test to determine your blood type. You got the following result: If you receive type AB blood for blood transfusion, what is going to happen and why?
Describe how to determine whether a patient has ever had a Salmonella typhi infection, the name of method, reagents used, possible results, conclusions deduced from results and why. She placed each preparation in a separate tube, labeled the tubes with a water-soluble marker, and left them in an ice bucket. When the instructor returned, she discovered that the labels had smeared and were unreadable.
Determined to salvage the antibodies, she relabeled the tubes 1, 2, 3, and 4 and proceeded. Based on the test results described below, indicate which preparation was contained in each tube and explain why you so identified the contents.
These sedimented red cells are examined macroscopically with the naked eye for agglutination, or they may be spread on a slide and viewed through a low-power microscope. An antibody that agglutinates red cells when they are suspended in saline solution is called a complete antibody.
Interactions between antigen and antibody - Wiki
With powerful complete antibodies, such as anti-A and anti-B, agglutination reactions visible to the naked eye take place when a drop of antibody is placed on a slide together with a drop containing red cells in suspension. After stirring, the slide is rocked, and agglutination is visible in a few minutes. It is always necessary in blood grouping to include a positive and a negative control for each test.
An antibody that does not clump red cells when they are suspended in saline solution is called incomplete.
Factors affecting the antigen-antibody reaction
Such antibodies block the antigenic sites of the red cells so that subsequent addition of complete antibody of the same antigenic specificity does not result in agglutination. Incomplete antibodies will agglutinate red cells carrying the appropriate antigen, however, when the cells are suspended in media containing protein. Serum albumin from the blood of cattle is a substance that is frequently used for this purpose.
Red cells may also be rendered specifically agglutinable by incomplete antibodies after treatment with such protease enzymes as trypsin, papain, ficin, or bromelain.
After such infections as pneumoniared cells may become agglutinable by almost all normal sera because of exposure of a hidden antigenic site T as a result of the action of bacterial enzymes.
When the patient recovers, the blood also returns to normal with respect to agglutination. The presence of an acquired B antigen on the red cells has been described occasionally in diseases of the colon, thus allowing the red cell to express an antigenicity other than that genetically determined.
In other diseases a defect in antibody synthesis may cause the absence of anti-A and anti-B antibody. Afterwards, antibody-producing B cells undergo rapid cell divisions in the germinal centres, during which the diversity of the binding sites is greatly amplified by casual mutations somatic hypermutation.
B cells producing high affinity antibodies are then preferentially selected for proliferation. In fact, early antibodies are coded by genes identical to those found in the germline, while mature antibodies are the product of somatically acquired point mutations Therefore, both affinity maturation and the seemingly impossible task of recognising a potentially infinite epitope repertoire with a finite paratope array, are fulfilled by the same mechanism, i.
Conversely, the increased rigidity of the binding site of the mature antibody abolishes cross-reactivity but entails favourable entropic changes during antigen binding 25although enthalpic factors may also be involved Re-stimulation of anti-D with D-positive red cells in immunised volunteers was accompanied by an increase in the equilibrium constant from 0.
However, affinity maturation of red cell antibodies produced by non-deliberate immunisation has not been documented by reaction kinetics studies. Factors affecting the antigen-antibody reaction Many factors influence antigen-antibody reactions. They can be conveniently classified in two groups, according to whether they act on the equilibrium constant or not Table IV.