Immunoglobulins, also called antibodies, are produced by the body's immune system. These antibodies attack cancer cells and foreign pathogens, such as bacteria, viruses and fungi. The immunoglobulins lgG and lgM are two of the body's five primary antibody types. There are a number of possible causes for low levels of these immunoglobulins, as well as numerous factors that are associated with reduced levels.
Immunoglobulin G (lgG)
Immunoglobulin G (lgG) is the smallest antibody within the immune system. The antibody is also the most abundant, comprising 75 to 80 per cent of the body's immunoglobulins. The lgG antibody is important for fighting bacterial and viral infections, and is found throughout the blood system. This immunoglobulin is the only antibody capable of crossing the placenta during pregnancy.
Immunoglobulin M (lgM)
Immunoglobulin M (lgM) is the largest antibody produced by the body's immune system. This antibody is found in both the blood and lymph fluid, comprising 5 to 10 per cent of the body's antibodies. The lgM antibody is the first immunoglobulin produced in response to an infection. The antibody also causes other immune system cells to attack pathogens.
Causes of Low lgG
Most lgG deficiencies are the result of inherited diseases. Low lgG can be caused by macroglobulinemia, also referred to as hyper-lgM syndromes. This is a condition where high levels of lgM interfere with the cells that produce lgG, preventing their growth. Other causes include nephritic syndrome, some types of leukaemia and common variable immunodeficiency. Research has also noted several other possible causes, including X-linked agammaglobulinemia, thymomas, stage III-IV retinoblastoma, transient hypogammaglobulinemia of infancy, and combined immune deficiencies, such as reticular dysgenesis. Certain drugs may also cause low lgG, including nonsteroidals, immunosuppresives and certain anticonvulsant agents, such as phenytoins. Radiation therapy is also a common cause of low lgG. Several factors have been associated with lowered levels of lgG, including intense exercise, excessive physical stress, smoking, moderate alcohol use, febrile seizures and ageing.
Causes of Low lgM
Low levels of lgM can be caused by multiple myelomo, some types of leukaemia, and some inherited types of immune diseases. Low lgM can also be caused by selective immunoglobulin M (SlgM) deficiency, a rare form of dysgammaglobulinemia. The causes of SlgM deficiency are unknown, and no link to familial inheritance has been established. Secondary SlgM deficiency is the most common form, and it has been associated with a number of conditions. One such condition is malignant neoplasms, such as clear cell sarcoma, Bloom syndrome and promyeloctic leukaemia. Another associated condition is autoimmune diseases, such as rheumatoid arthritis, Hashimoto thyroiditis, systemic lupus erythematosus and autoimmune hemolytic anaemia. Infections, such as Brucella, and immunosuppressant agents, may also produce secondary SlgM deficiency. Associations have also been noted with gastrointestinal disorders, including Crohn disease, chronic diarrhoea, lymphoid nodular hyperplasia, Whipple disease and splenomegaly.