IMMUNE COMPLEX TEST

The immune complex test is a test designed to evaluate the status or proper functioning of the immune system. The criterion used to evaluate the operation of the immune system is via the presence of so-called immune complexes.

An immune complex is an association formed between large numbers of antigens and the corresponding antibodies. The latter are produced in a specific response to the presence of the antigen, which has been perceived as being foreign by the body's immune system. The individual antigen-antibody complexes can associate together to form the interlocking network that represents an immune complex.

Normally, immune complexes are removed from the bloodstream by specialized cells of the spleen called macrophages and by other specialized cells located in the liver. However, if this clearance does not occur, the immune complexes will continue to circulate, and will become trapped in the kidneys, lung, skin, joints, or blood vessels. The specific location depends on the composition of the complex. Their presence will cause inflammation and can lead to tissue damage.

Immune complexes can develop as a result of what is termed a low-grade persistent infection. Examples include Streptococcus viridans infection of the blood, Staphylococcus heart infections, and viral hepatitis. Second, immune complexes can form in response to the continued exposure to an antigen, such as the repeated inhalation of mold in a farming or animal care facility. Finally, immune complexes are often a hallmark of autoimmune diseases. The continual response of the body's immune system overloads the ability of the body to remove the immune complexes that form. Examples of autoimmune diseases for which an immune test is beneficial in terms of diagnosis are systemic lupus erythematosus, rheumatoid arthritis, Lyme disease and human immunodeficiency virus infection.

Being able to test for the presence of abnormal levels of immune complexes can alert the physician to an abnormal function of the immune system, such as an autoimmune disorder.

Immune complexes can be detected by the application of special stains to tissue that has been obtained from a patient. The stains contain antibodies that bind to the complexes and this binding is highlighted by the presence of the staining agent. This test is useful because it directly detects the presence of the immune complexes. However, for routine clinical use, this method is cumbersome and invasive. This has stimulated the development of blood tests that indirectly detect the complexes in the blood serum.

There are several methods available. Often more than one will be used to test the same sample. This is because the test methods are not yet uniformly standardized across the medical community. But, if the results from several tests are positive for immune complexes, the validity of the diagnosis is ensured.

Immune complex tests include the Raji cell, C1q binding, conglutinin, and anti-C3 assays. The Raji cell assay, for example, detects the immune complexes following the binding of the complexes with an immune molecule called complement. In addition, the complement has been labeled with a compound known as fluorescein isothiocyanate. The latter compound is able to fluoresce when light of a certain wavelength is shone on it. The detection occurs in a machine called a flow cytometer, in which fluid moves past a detector that is programmed to detect certain chemical aspects. In the Raji cell assay, detection of the fluorescent isothiocyanate indicates the presence of the immune complex.

A normal result in an immune complex test is a negative result. In other words, immune complexes are normally absent.