Immunofixation

Principle

It is a method of detection by precipitation, i.e. when one puts in contact the soluble (Ag) antigen with the corresponding antibody, it occurs a phenomenon of precipitation, visible with the naked eye or with an apparatus.

The immunofixation makes it possible to identify Antigène S (monoclonal immunoglobulins) in a mixture, according to their electrophoretic mobility. To allow this identification one uses Anticorp S specific to these Ag.

The immunofixation in particular makes it possible to detect monoclonal immunoglobulins present in diseases such as the Myélome or the Maladie of Waldenström.

Technique

It consists in depositing plasma (or urine which will have been concentrated as a preliminary) on a gel. After application of an electric current which allows the separation of proteins according to their size, of the specific antibodies of each type of immunoglobulin are deposited on freezing. It thus appears more or less narrow bands on freezing, on the level where the various immunoglobulins are located.

The immunofixation, like the immunoelectrophoresis, is held in two stages:

the first stage is identical for the two techniques. It consists in depositing the antigens contained in plasma or the urines on a gel, then to separate these antigens according to their electrophoretic mobility by making them migrate under the effect of an electric field. This migration depends on the mass and the load of the antigen. Once Ag separated, one can pass at the following stage.
the second phase is function of the technique used. The immunofixation requires to make migrate the serum tested several times. For that the antibodies are not deposited in a drain, as in the electrophoresis, but are added individually on each track of migration of different Ag. The presence of a monoclonal immunoglobulin results in the appearance of a narrow band after coloring of the precipitated complexes. For example, if it is about IgG L, one will observe a narrow band, at the same time, on the track where the anti-g one as on that was deposited where the antione was deposited.

Advantages

The immunofixation tends to supplant the immunoelectrophoresis because it with the advantage of being:

faster (deadline for reply in less than three hours);
a little more sensitive, thus the immunofixation can reveal Ig last unperceived with the electrophoresis, in particular when it is present in minor amount (less than 1 gram/liter);
partly automatizable and thus realizable by a greater number of laboratories;
easier to read and interpret.

Disadvantages

The immunofixation has like principal disadvantage:

to be unaware of the exploration of serum proteins completely others that immunoglobulins;
it is more expensive than the immunoelectrophoresis.

External bonds

Technical immunological on the site of Southern the Paris medical college
Immunoelectrophoresis and fixing on the site of e-sante.be

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