The immune system protects against foreign invaders. Antibodies, also known as immunoglobulins, identify and neutralize harmful substances like bacteria and viruses. Immunoglobulin G (IgG) is the most abundant antibody, playing a central role in the body’s long-term protection. Understanding low IgG levels and their health implications is important.
Role of Immunoglobulin G
Immunoglobulin G (IgG) is an antibody produced by plasma B cells. It is the most common antibody in blood, comprising 70% to 75% of all immunoglobulins. IgG provides long-lasting protection against infections, including bacteria, viruses, and fungi.
IgG antibodies bind to specific foreign substances, called antigens, on pathogens. This binding neutralizes the pathogen, preventing it from entering body cells. IgG also marks pathogens for destruction by other immune cells and activates the complement system, which helps eliminate infected cells. IgG is the only antibody that can cross the placenta from mother to baby, providing passive immunity to the newborn baby.
Signs of Low IgG
Low Immunoglobulin G levels compromise the immune system’s ability to fight infections. Individuals frequently experience recurrent infections, particularly respiratory tract infections like sinusitis, bronchitis, and pneumonia. Ear infections are also common and may be persistent or severe.
Gastrointestinal infections, such as chronic diarrhea, and frequent skin infections are other signs. Infections can be unusually severe, prolonged, or difficult to treat. In infants and children, poor growth or inadequate weight gain can also indicate low IgG levels. These symptoms suggest impaired immune function, requiring medical evaluation.
Reasons for Low IgG Levels
Low Immunoglobulin G levels stem from primary or secondary immunodeficiencies. Primary immunodeficiencies are genetic conditions where the body does not produce sufficient or functional antibodies. Examples include Common Variable Immunodeficiency (CVID), where individuals have low levels of IgG, IgA, and sometimes IgM. X-linked agammaglobulinemia (XLA) is another primary immunodeficiency characterized by extremely low or absent B-cells, resulting in a profound lack of antibodies, including IgG. Transient Hypogammaglobulinemia of Infancy (THI) is a temporary delay in an infant’s IgG production, often resolving as the child matures.
Secondary immunodeficiencies occur when low IgG levels develop from another disease or external factor. Certain medications can suppress antibody production, including immunosuppressants, some anti-seizure drugs, and chemotherapy. Chronic medical conditions also contribute to low IgG, such as kidney disease, which can lead to excessive protein loss in urine, or certain cancers like chronic lymphocytic leukemia (CLL) and multiple myeloma, which affect immune cell production. Malnutrition can impair immune function, while severe burns or protein-losing enteropathy can result in significant IgG loss.
Identifying and Addressing Low IgG
Identifying low Immunoglobulin G involves blood tests to measure antibody levels (IgG, IgA, IgM). A healthcare provider interprets these results alongside a patient’s symptoms and medical history. If low IgG is detected, further tests may be needed to pinpoint the exact cause, such as assessing vaccine response or genetic testing.
Addressing low IgG levels depends on the deficiency’s severity and cause. For primary or severe secondary cases, Immunoglobulin Replacement Therapy (IRT) is standard, administering pooled antibodies from healthy donors, typically via IVIG or SCIG. IRT provides missing antibodies, reducing infection frequency and severity. For secondary low IgG, treatment focuses on managing the underlying condition, such as adjusting medication, treating kidney disease or cancer, or addressing nutritional deficiencies. Prompt infection treatment and prophylactic antibiotics also protect individuals with compromised IgG levels.