Immunoglobulin G (IgG) protein is a fundamental part of the body’s defense system. It is the most common type of antibody found in the bloodstream, accounting for about 75% of all antibodies in human serum. IgG molecules circulate throughout the blood and extracellular fluid. They are specialized proteins produced by immune cells, designed to recognize and neutralize foreign invaders.
The Role of IgG in the Immune System
One primary action is neutralization, where IgG antibodies directly bind to pathogens like viruses and bacteria. This binding prevents these invaders from attaching to and entering body cells. By doing so, IgG stops the spread of infection within the body.
Another function is opsonization, where IgG antibodies “tag” or coat the surface of pathogens. This tagging makes the invaders more visible and recognizable to other immune cells, such as phagocytes, which are specialized cells that engulf and destroy foreign particles. Opsonization significantly enhances the efficiency of pathogen clearance from the body.
IgG also plays a role in immune memory, providing long-lasting protection against previously encountered pathogens. After an initial infection or vaccination, the body produces specific IgG antibodies that remain in circulation for extended periods, sometimes years or decades. If the same pathogen is encountered again, these memory IgG antibodies enable a faster and stronger immune response.
IgG can cross the placenta from mother to fetus. This transfer provides passive immunity to the developing fetus and, subsequently, to the newborn during their first few months of life. This maternally acquired IgG offers protection against infections before the infant’s own immune system fully develops its capacity to produce antibodies.
IgG Levels and Health
Measuring IgG levels in the blood offers important insights into a person’s immune status. Abnormal IgG levels can indicate underlying health issues.
Low IgG levels, a condition known as hypogammaglobulinemia, signify a weakened immune system. Individuals with this condition are more susceptible to recurrent infections, particularly those affecting the respiratory and gastrointestinal tracts. Hypogammaglobulinemia can be primary, resulting from genetic disorders affecting antibody production, or secondary, caused by other medical conditions or medications. Examples of secondary causes include certain cancers like chronic lymphocytic leukemia, kidney disease leading to protein loss, or immunosuppressive drugs.
Conversely, elevated IgG levels, termed hypergammaglobulinemia, can also point to various health concerns. This increase often indicates an ongoing or recent infection, as the immune system produces more antibodies to fight off the pathogen. Autoimmune disorders, where the immune system mistakenly attacks the body’s own tissues, can also lead to high IgG levels due to chronic inflammation. Certain types of blood cancers, such as multiple myeloma, are another potential cause of elevated IgG, as these conditions involve the uncontrolled production of abnormal antibodies.
IgG in Medical Treatments
Intravenous Immunoglobulin (IVIg) therapy is a medical application of IgG for a range of conditions. IVIg is a solution derived from the pooled plasma of thousands of healthy blood donors. This meticulous process ensures a broad spectrum of antibodies, and the product undergoes rigorous testing and purification to minimize the risk of transmitting infections.
One primary use of IVIg is replacement therapy for patients who cannot produce sufficient amounts of their own IgG antibodies. This includes individuals with primary immunodeficiencies, such as common variable immunodeficiency (CVID), or those with secondary immunodeficiencies caused by certain diseases or treatments like chemotherapy. Administering IVIg helps these patients maintain protective antibody levels, reducing their susceptibility to recurrent and severe infections.
IVIg is also used for its immunomodulatory effects, particularly in autoimmune and inflammatory diseases where the immune system is overactive. In these conditions, high doses of IVIg can help regulate the immune response, preventing the body from attacking its own cells and tissues. This approach is utilized in conditions such as Guillain-Barré syndrome, chronic inflammatory demyelinating polyneuropathy, and certain rheumatological disorders. The therapy aims to dampen the harmful immune activity, thereby alleviating symptoms and improving patient outcomes.
External Sources of IgG
Beyond the body’s natural production and pharmaceutical treatments, some external sources of IgG are available, primarily in the form of dietary supplements. Bovine colostrum, the first milk produced by cows after calving, is a notable example, as it is rich in immunoglobulins, including IgG. These supplements are marketed for their potential to support human gut health and bolster the immune system.
The IgG found in bovine colostrum is critical for the immunity of newborn calves, offering them passive protection against various pathogens. While bovine colostrum contains immune-active components, its effectiveness and direct benefits for human adults are still under scientific investigation. Some studies suggest that bovine IgG may offer localized protection in the human gastrointestinal tract and potentially reduce the incidence of upper respiratory and gastrointestinal infections. However, the extent to which bovine IgG is absorbed and functions systemically in humans, similar to the body’s own IgG, is not fully established.