The presence of many single-stranded antibodies that bind to DNA often result from autoimmune reactions or viral infections. Autoimmunity describes the situation in which a body’s healthy cells are being attacked by its own immune system. There are over 80 different autoimmune diseases in humans, but the reason why they occur is unknown. However, there may be a genetic factor since autoimmune diseases tend to run within families
Antibodies are produced by immune cells called B lymphocytes (B cells). An antibody is a protein that recognizes and sticks to foreign particles. Antibodies serve many functions, including trapping and weighing down foreign particles and binding to foreign invaders so that other immune cells know who the invaders are. Each antibody only recognizes a specific type of foreign particle, whether it’s a protein molecule, sugar molecule, fat molecule or DNA molecule. In autoimmune diseases, a person’s healthy cells are attacked, and the DNA inside those cells is released. B cells find this DNA and think that it belongs to a foreign invader. The B cells then produce antibodies that bind to this DNA. This normally shouldn’t happen, so the presence of high levels of antibody against single-stranded DNA may indicate an autoimmune disease.
Multiple sclerosis (MS) is the most common disabling neurological disorder in young adults. It results in an attack on nerve cells in the brain and spinal cord by immune cells of the body. Clusters of different immune cell types, including B cells, can be found surrounding plaques, which are regions of attack in the brain and spinal cord. How do anti-DNA antibodies affect normal cells in MS? Normal cells store their DNA inside their nucleus, which is deep inside a cell. Antibodies cannot pass through the cell’s outer membrane, so they cannot bind to the DNA that is inside the nucleus. However, cells have some DNA that is attached to its outer surface in the form of what is called DNA-histone complexes. The anti-DNA antibodies produced by B cells attack healthy cells by attaching to this surface DNA.
Systemic Lupus Erythematosus
Systemic Lupus Erythematosus (SLE) is an autoimmune disease in which the immune system attacks many organs, including the kidneys, skin and brain. Kidney damage is the most important feature of SLE that affects long-term survival of the patient. Anti-DNA antibodies have been found to bind the wall of the glomerulus, which is the filtration bulb at the beginning of the filtration tube in the kidney. A kidney has many of these filtration tubes, which filters the waste products out of the blood stream. Anti-DNA antibodies not only bind to the DNA that is on the surface of the cells lining the glomerulus, but they also bind to sugar molecules on this surface. Cells on the glomerulus have a sugar molecule called heparin-sulfate, which happens to attract anti-DNA antibodies.
Hepatitis B is a single-stranded DNA virus, meaning the genetic information that it carries is in the form of a single-strand of DNA. Hepatitis B causes liver damage and liver cancer in many people throughout the world. Research has shown that people who are infected with hepatitis B produce antibodies against the single-stranded DNA of this virus. The amount of these antibodies flowing in a person’s blood stream can be used to diagnose whether that person is infected.
- MedlinePlus: Autoimmune Diseases
- Molecular Biology of the Cell: B Cells and Antibodies
- Proceedings of the National Academy of Sciences: Anti-DNA Antibodies are a Major Component of the Intrathecal B Cell Response in Multiple Sclerosis
- MedlinePlus: Systemic Lupus Erythematosus
- Loyola University Chicago: Viral Hepatitis B
- Journal of Medical Virology: Antibodies to Single Stranded DNA: A Diagnostic Aid in Chronic Hepatitis B Virus Infections
- Jeffrey Hamilton/Digital Vision/Getty Images