How Immune Complexes are detected?

There are many tests for the detection of immune complexes in persons with suspected symptoms of Type III hyper sensitivity reactions. Since the clinical syndromes are different in different individuals and in different levels of reactions, no single test is adequate at all situations.

Since the identity of an antigen is often unknown, detection of specific antigen is not always possible. Certain tests in present use at present are as follows.

1. Immunofluorescence Test

If the physical characteristics of antigen are known, tissue samples can be studied by immunoflurescence for the presence of antigen and Ab complex by laser nephelometry.

Since polyethylene glycol (PEG) has the capacity to precipitate high molecular weight immune complexes, serum samples can be added to buffer, containing PEG, to precipitate Ag -Ab complex that can be monitored by laser nephelometry.

2. Platelet Aggregation Test

If we know the adhering tendency of antigen to cell membrane, Ag -Ab complexes can be detected via the platelet aggregation test. Since Ag-Ab complexes interact with membrane surface of blood platelets and cause aggregation the presence of platelets in test sample can be studied either visually with a microscope, or electrically by means of changes in turbidity measurements.

The platelet aggregation test measures the rate and degree to which dispersed platelets in a sample of plasma (the liquid portion of blood) form clumps after the addition of a material that normally stimulates aggregation. These materials may include adenosine diphosphate (ADP), epinephrine, arachidonic acid, collagen, or ristocetin. Clumping of platelets causes the sample to be more clear (less turbid). A machine measures the changes in turbidity (cloudiness) and prints a graphic recording of the results.

Test with Radio Labeled Anti-IgG Abs

In this assay the property of Ag-Ab complex interaction with certain components of the complement system is exploited.

The serum samples are exposed to Clq component of complement system bound to the sides of the test tube. If immune complexes are present, they bind to the Clq.

Following incubation, sample is removed and again incubated with radio labelled Anti-IgG Abs. The amount of radioactivity correlates with the concentration of immune complexes in the serum sample. This character has provided a basis for a novel therapeutic procedure called Plasmapheresis.

Individuals with certain immune complex disorders can be treated by Plasmapheresis, to remove immune complxes from their serum.

The therapy is performed with an automatic continuous flow of blood through cell separator machine that removes the large immune complexes and returns the cleared plasma to the individual.