Immunofixation

Immunofixation permits the detection and typing of monoclonal antibodies or immunoglobulins in serum or urine. It is of great importance for the diagnosis and monitoring of certain blood related diseases such as myeloma.

Principle

The method detects by precipitation: when a soluble antigen (Ag) is brought in contact with the corresponding antibody, precipitation occurs, which may be visible with the naked eye or microscope.

Immunofixation identifies (antibodies) in a mixture in function of their specific electrophoretic mobility. For the identification antigens are used that are specific for the targeted antibody.

Specifically, immunofixation allows the detection of monoclonal antibodies representative of diseases such as myeloma or Waldenström macroglobulinemia.

Technique

It consists of depositing the serum (or urine which has been previously concentrated in) on a gel. After application of an electric current that allows the separation of proteins according to their size, antibodies specific for each type of immunoglobulin were laid upon the gel. It thus appears the more or less narrow bands on the gel, which are at different immunoglobulins.

Immunofixation as immunoelectrophoresis, takes place in two steps:

• The first step is identical for both techniques. It consists in depositing the immunoglobulins contained in the serum or urine on a gel and then separating the immunoglobulins according to their electrophoretic mobility by making the them migrate under the effect of an electric field. This migration depends on the mass and charge of the antigen. Once the immunoglobulins are separated, we can move to the next step.
• The second step is based on the technique used. Immunofixation requires electrophoresis to migrate serum proteins in replicate. Then, specific anti-immunoglobulin antisera are used to treat each replicate. For this, the antisera are not placed in a channel, as in electrophoresis, but they are added individually to each migration lane. The presence of a monoclonal immunoglobulin results in the appearance of a narrow band after staining complex precipitates. For example, in the case of an IgG lambda, there will be a narrow band, both on the track on which was deposited anti-G and on which has been deposited with the anti-lambda.

Merits

Immunofixation tends to replace protein electrophoresis because  :

• it is faster (results within three hours) ;
• it is somewhat more sensitive. Immunofixation may reveal an immunoglobulin missed out by protein electrophoresis, especially at low concentrations (less than 1 gram/litre) ;
• it can be partially automated and can be used in more laboratories;
• it is more easily read and interpreted.

Demerits

Immunofixation is however only sensitive to immunoglobulins and is more expensive than protein electrophoresis.

Sources

• fr:Immunofixation

See also

• Immunoelectrophoresis

External links

• MedlinePlus Encyclopedia 003543 - "Immunofixation - serum"
• MedlinePlus Encyclopedia 003593 - "Immunofixation - urine"
• Diagram at University of Pittsburgh School of Medicine