Microbiology and Immunology

I

285

•

IGA•seeIMMUNOGLOBULINS AND IMMUNOGLOBULIN DEFI-

CIENCY SYNDROMES

IGA DEFICIENCY•seeIMMUNODEFICIENCY DISEASE

SYNDROMES

IGD• seeIMMUNOGLOBULINS AND IMMUNOGLOBULIN DEFI-

CIENCY SYNDROMES

IGE•seeIMMUNOGLOBULINS AND IMMUNOGLOBULIN DEFI-

CIENCY SYNDROMES

IGG •seeIMMUNOGLOBULINS AND IMMUNOGLOBULIN DEFI-

CIENCY SYNDROMES

IGG SUBCLASS AND SPECIFIC ANTIBODY

DEFICIENCIES•seeIMMUNODEFICIENCY DISEASE SYN-

DROMES

IGM•seeIMMUNOGLOBULINS AND IMMUNOGLOBULIN DEFI-

CIENCY SYNDROMES

IImmune complex testMMUNE COMPLEX TEST

The immune complex test is a test designed to evaluate the sta-

tus 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 net-

work 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 com-

plexes will continue to circulate, and will become trapped in the

kidneys, lung, skin, joints, or blood vessels. The specific loca-

tion depends on the composition of the complex. Their presence

will cause inflammationand can lead to tissue damage.

Immune complexes can develop as a result of what is

termed a low-grade persistent infection. Examples include

Streptococcus viridansinfection of the blood, Staphylococcus

heart infections, and viral hepatitis. Second, immune com-

plexes can form in response to the continued exposure to an

antigen, such as the repeated inhalation of moldin 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, rheuma-

toid arthritis, Lyme diseaseand human immunodeficiency

virusinfection.

Being able to test for the presence of abnormal levels of

immune complexes can alert the physician to an abnormal func-

tion 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 pres-

ence of the immune complexes. However, for routine clinical

use, this method is cumbersome and invasive. This has stimu-

lated 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

womi_I 5/6/03 3:23 PM Page 285