Anti-SR Protein Antibody Assay - Diagnostic Test for Lupus

Note: In August 2002, the Anti-SR protein antibody assay test was cleared for marketing by the FDA.

Lupus Erythematosus Difficult to Diagnose

People with lupus produce abnormal antibodies in their blood which target tissues within their own body. Lupus is one of the autoimmune diseases. The chronic inflammation which is associated with this lupus can affect the:

• skin
• heart
• lungs
• kidneys
• joints
• nervous system

When only the skin is affected, the condition is known as discoid lupus. When other internal organs are affected, the condition is known as systemic lupus erythematosus. Approximately 8 times more women than men are diagnosed with lupus.

Some patients with lupus erythematosus can be difficult to diagnose since symptoms of the disease are quite variable, ranging from skin rash to fatigue to organ failure. Most lupus patients produce antibodies to their own tissues, detectable by a blood test which has been available since the 1950s. About 20 percent of patients with lupus do not make the antibodies though and go undiagnosed.

The Discovery

Scientists at the Fred Hutchinson Cancer Research Center in Seattle, Washington, lead by Mark Roth, Ph.D., have developed a new diagnostic test for lupus, later named anti-SR protein antibody assay, which promises to improve detection of the autoimmune disease. The Hutchinson Center has filed for patent protection of the new assay system.

Working as a basic sciences investigator 14 years ago at Hutchinson, Roth injected mice with extracts from frog nuclei. At the time, Roth did not know nor could he predict that antibodies produced by the mice would identify a group of proteins, known as SR proteins.

Roth also could not foretell that his discovery would lead to years of subsequent research on biological processes which occur in the nuclei of every animal. Although Roth and his colleagues did not set out to develop a new diagnostic test for lupus, through his work it was discovered that SR proteins are indeed indicators of lupus because most patients produce antibodies to them.

The Test

Roth's experiment and discovery has generated the development of a color-coded test for the purpose of detecting SR proteins in serum. In the test, sera (the clear portion of blood) is added to tiny wells in a plastic plate which have been coated with human SR proteins. Antibodies in the sera which adhere to the SR proteins are detected by a colored molecular tag. Sera from lupus patients turns purple. Sera from non-lupus individuals remains clear. The test can identify 50 to 70 percent of lupus patients who react positively to SR proteins.

SR Proteins

SR proteins are highly modified. Once a cell makes SR proteins, it modifies them by placing non-protein molecules onto them. The cell adds large numbers of phosphate groups in the case of SR proteins. A healthy immune system recognizes the body's own proteins. Roth believes that the recognition occurs as phosphates and other modifications are stripped off. Roth also has suggested that in lupus the body may fail to strip off certain modifications thereby generating antibodies against the bodies own proteins, including SR proteins.

Related Resources

_{Sources: Testing For Lupus, Center News, May 4, 2000; New Diagnostic Test For Lupus To Bridge Detection Gap, PRNewswire, August 7, 2000; FDA Clears For Market New Diagnostic Test For Lupus, Fred Hutchinson Cancer Research Center, Aug. 28, 2002}