Immunoglobulin G (IgG) is an antibody produced by the immune system to fight infections. It is the most abundant antibody in human blood, making up about 75% of all serum antibodies. These Y-shaped proteins are key components of the body’s defense, providing long-term protection against various pathogens.
IgG antibodies consist of two heavy and two light chains. This structure allows IgG to bind to specific targets, called antigens, unique markers on foreign invaders like viruses, bacteria, and fungi. Once bound, IgG prevents pathogens from attaching to cells, effectively neutralizing them.
IgG antibodies play a significant role in the secondary immune response, quickly recognizing and targeting pathogens the body has encountered before to prevent illness. Beyond direct neutralization, IgG alerts other immune cells to destroy pathogens by coating them (opsonization), or by activating the complement system to eliminate the threat.
IgG is widely distributed throughout the body, found in blood and extracellular fluid, controlling infections within tissues. A unique property of IgG is its ability to cross the placenta from mother to fetus. This provides passive immunity to the infant before their own immune system is fully developed, protecting against maternal infections.
Causes and Indicators of Low IgG
Low immunoglobulin G (IgG) levels stem from primary or secondary immunodeficiencies. Primary immunodeficiencies are genetic disorders causing insufficient antibody production. Common Variable Immunodeficiency (CVID) is a primary condition characterized by low IgG, often alongside IgA and/or IgM, frequently diagnosed in adulthood. X-linked agammaglobulinemia (XLA), a genetic disorder primarily affecting males, prevents the body from producing B cells, essential for antibody production.
More common secondary causes develop later in life due to external factors or other medical conditions. Certain medications, like immunosuppressants, chemotherapy drugs, and long-term corticosteroids, can suppress the immune system and reduce IgG levels. Kidney disease, particularly nephrotic syndrome, can cause significant protein loss, including IgG, through the urine. Specific cancers, such as lymphomas, leukemias, and multiple myeloma, directly affect immune cells responsible for antibody production, leading to low IgG.
Chronic infections, like Human Immunodeficiency Virus (HIV), can weaken the immune system and decrease antibody production. Severe malnutrition can also impair protein synthesis, including immunoglobulins, leading to lower IgG levels.
Indicators of low IgG often include recurrent, severe, or unusually prolonged infections, particularly affecting the respiratory tract. Individuals may experience frequent sinus infections, ear infections, bronchitis, and pneumonia. Skin infections and gastrointestinal issues, such as chronic diarrhea, are also common. A poor response to standard antibiotic treatments is another indicator, as the immune system lacks the IgG antibodies to clear infection. Chronic fatigue is also frequently reported.
Diagnosis and Treatment Approaches
Diagnosing low IgG levels begins with a thorough medical history and physical examination to assess symptoms and infection patterns. Blood tests measure serum immunoglobulins, specifically IgG, IgA, and IgM. If initial tests indicate low IgG, further specialized evaluations may be necessary.
Specialized tests include antibody titers, which assess the body’s ability to produce specific antibodies in response to vaccines like tetanus or pneumonia. A poor response to these vaccines can indicate impaired immune function, even if total IgG levels are within a normal range. Serum protein electrophoresis is another test that can detect abnormal protein patterns, including reduced gamma globulin levels, which primarily consist of antibodies.
Treatment strategies for low IgG are tailored to the specific cause and symptom severity. For primary immunodeficiencies, immunoglobulin replacement therapy (IgRT) is a standard approach. This involves administering concentrated IgG antibodies from healthy donors, either intravenously (IVIG) or subcutaneously (SCIG). These infusions provide missing antibodies, helping to prevent serious infections and improve overall immune function.
For secondary low IgG, managing the underlying condition is important. This might involve adjusting immune-suppressing medications, treating kidney disease to reduce protein loss, or managing cancers that affect antibody production. Prophylactic antibiotics may also be prescribed to prevent recurrent infections, especially while the underlying cause is being addressed or in conjunction with IgRT.