Lupus antibodies are proteins produced by the immune system that mistakenly target the body’s own healthy tissues. Normally, antibodies identify and neutralize foreign invaders like bacteria and viruses. In lupus, the immune system becomes overactive, producing “autoantibodies” that attack self-cells as if they were threats, causing inflammation and damage. These autoantibodies are a distinctive feature of lupus, an autoimmune disease that can affect various parts of the body.
Key Types of Lupus Antibodies and Their Importance
Antinuclear Antibodies (ANA) are the most common initial screening test for lupus, found in about 98% of people with systemic lupus. A positive ANA result indicates autoimmunity, meaning the immune system produces antibodies against the cell’s nucleus. However, it does not definitively diagnose lupus, as other autoimmune conditions or even healthy individuals can have a positive ANA. The pattern observed in the ANA test, such as a homogenous or peripheral pattern, can offer additional clues, with a peripheral pattern being almost exclusive to systemic lupus.
More specific antibodies are then tested to help confirm a lupus diagnosis. Anti-double-stranded DNA (anti-dsDNA) antibodies are found in 30-70% of people with systemic lupus and are highly specific to the disease, rarely appearing in healthy individuals. High levels of anti-dsDNA often indicate more severe lupus, particularly kidney involvement (lupus nephritis), and can be used to monitor disease activity. Anti-Smith (anti-Sm) antibodies are also highly specific to lupus, present in 20-40% of cases, and are rarely found in other rheumatic diseases or healthy individuals.
Other relevant antibodies include anti-Ro/SSA and anti-La/SSB, found in 30-40% and 10-15% of lupus patients, respectively, and are also common in Sjögren’s syndrome. These antibodies are important during pregnancy due to their association with neonatal lupus and congenital heart block in infants. Anti-ribonucleoprotein (anti-RNP) antibodies are found in many autoimmune conditions, including lupus, and high levels in the absence of other autoantibodies might suggest mixed connective tissue disease. Anti-histone antibodies are often seen in drug-induced lupus, which resolves after discontinuing the offending medication.
Detecting Lupus Antibodies
Detecting lupus antibodies involves a blood test. A doctor may order these tests if a patient exhibits symptoms suggestive of an autoimmune condition. The process begins with drawing a blood sample, which is then sent to a laboratory for analysis.
One common laboratory method used for ANA testing is indirect immunofluorescence (IFA). In this method, the patient’s blood serum is added to a slide containing specific cells. If antinuclear antibodies are present, they will bind to the cell nuclei. A second antibody, tagged with a fluorescent dye, is then added, which attaches to the bound serum antibodies, making them visible under a fluorescence microscope. For specific antibodies like anti-dsDNA, methods such as enzyme-linked immunosorbent assay (ELISA) or the Crithidia luciliae immunofluorescence test are used.
Understanding Lupus Antibody Test Results
Lupus antibody test results are interpreted in the context of a patient’s symptoms and other clinical findings, as no single test can definitively diagnose lupus. A “positive” result for an antibody indicates its presence in the blood, while “negative” means it was not detected or was below a certain threshold. For ANA tests, results are often reported as a “titer,” such as 1:80 or 1:160, indicating how many times the blood sample was diluted before the antibodies were no longer detectable. Higher titers, like 1:320 or greater, are more indicative of an autoimmune disease, although lower titers can also be found in healthy individuals.
Doctors consider a combination of positive specific antibody tests, such as anti-dsDNA and anti-Sm, along with a patient’s clinical symptoms and other laboratory findings, to establish a diagnosis. These tests also play a role in monitoring disease activity and the effectiveness of treatment, as levels of certain antibodies like anti-dsDNA can fluctuate with disease progression.
How Lupus Antibodies Affect the Body
Lupus antibodies contribute to symptoms by driving an autoimmune process where the immune system mistakenly attacks the body’s own healthy cells and tissues. In lupus, immune cells produce autoantibodies that target the body’s own molecules, including DNA and RNA.
These autoantibodies form large clusters with their targets, known as immune complexes. These immune complexes can deposit in various organs and tissues, triggering inflammation and causing damage. This systemic inflammation can manifest in diverse ways, affecting different organ systems. For example, lupus can cause inflammation in the joints, leading to arthritis, or in the skin, resulting in rashes. It can also affect the kidneys, potentially leading to lupus nephritis, or the brain and nervous system, causing neurological symptoms. The chronic inflammation caused by this immune attack can lead to long-term scarring and jeopardize organ function.