A:
SLE can be associated with low IgG. Since you have SLE, that's the likely explanation. However, there are many other potential explanations.
IgG is a protein that functions as an antibody in the body's immune system. We make several types of immunoglobulin, including:
- immunoglobulin A (IgA)
This is found in mucous membranes. It is produced after being exposed to infectious agents or other proteins the body views as "foreign" - immunoglobulin D (IgD)
Its purpose is uncertain but it may "fine tune" the immune response and help other antibodies fight off infections - immunoglobulin E (IgE)
This antibody is most commonly produced as part of an allergic reaction - IgG
This antibody is usually produced weeks to months after being exposed to an infectious agent; there are 4 subtypes of IgG: IgG1, IgG2, IgG3, and IgG4. - immunoglobulin M (IgM)
This antibody is usually produced soon after being exposed to an infectious agent
Not having enough of these antibodies or subtype can cause illness. For example, low levels of IgG may be associated with frequent infections, such as pneumonia, ear infections or sinusitis. But many people have low levels of one or more of these without symptoms or related health problems.
While the cause of low IgG may be impossible to identify, a number of causes and associations have been discovered, including:
- genetic or developmental disorders of the immune system
- loss of protein due to digestive or kidney disease
- intense physical stress (such as prolonged exercise)
- smoking
- aging
- autoimmune disease, such as SLE and rheumatoid arthritis - Some SLE patients with low IgG have a protein loss due to kidney disease. Others have cells involved in IgG production that work abnormally
- medications, especially those that affect the immune system, such as corticosteroids
- certain blood disorders and tumors, such as myeloma and thymoma (a noncancerous tumor of the thymus, an organ located in the upper chest that is involved in immune development)
While your low IgG may be related to SLE, it's important that you and your doctor consider some of these other possibilities. See your doctor to determine the cause and to decide whether your low IgG needs treatment.
