Immunoglobulin A, commonly known as IgA, is a specific type of antibody that plays a significant role in the body’s immune system. Its presence is particularly important for protecting the body’s surfaces that are exposed to the external environment. When IgA levels are lower than normal, it can affect the body’s ability to defend against certain threats.
IgA and Its Immune Function
IgA is a primary defender within the body’s mucosal immune system, which acts as a barrier against foreign invaders. This antibody is abundantly found in secretions such as saliva, tears, breast milk, and the mucous membranes lining the respiratory, gastrointestinal, and genitourinary tracts. Its main function involves preventing pathogens, like bacteria and viruses, from attaching to and entering the body’s cells.
IgA achieves its protective role by binding to these harmful microorganisms, neutralizing or preventing their adherence to mucosal surfaces. This action helps to maintain the integrity of the body’s barriers, reducing the risk of infection and inflammation. For instance, in the gut, IgA can clump bacteria together, facilitating their removal from the body through the digestive process.
Genetic Predispositions to Low IgA
Low IgA levels can be rooted in an individual’s genetic makeup, indicating an inherited susceptibility. Selective IgA Deficiency (sIgAD) is the most common primary immunodeficiency, caused by inherited genetic defects. This condition is characterized by significantly reduced or absent IgA in the blood, despite normal levels of other antibody types like IgG and IgM.
Estimates suggest that sIgAD affects approximately 1 in 400 to 1 in 1000 individuals in Western populations. While many individuals with sIgAD remain asymptomatic, some may experience recurrent infections, particularly in the respiratory and gastrointestinal tracts. The underlying genetic basis for sIgAD is complex and involves multiple genes, though a clear pattern of inheritance is not always observed. Other, much rarer primary immunodeficiencies can also present with low IgA as part of a broader immune system dysfunction.
Acquired Factors Leading to Low IgA
Beyond genetic predispositions, a variety of acquired factors can lead to a reduction in IgA levels, which develop over a lifetime. Certain chronic health conditions are known to be associated with decreased IgA production. For example, celiac disease, an autoimmune disorder triggered by gluten, often leads to lower IgA due to chronic inflammation and damage to the small intestine. Inflammatory bowel diseases, such as Crohn’s disease and ulcerative colitis, can also contribute to reduced IgA through persistent intestinal inflammation.
Autoimmune conditions like systemic lupus erythematosus and rheumatoid arthritis may also correlate with lower IgA, due to the widespread immune dysregulation characteristic of these diseases. Specific medications can interfere with the body’s ability to produce IgA. Anti-seizure drugs, such as phenytoin, can cause reduced IgA levels in some patients by affecting antibody synthesis. Immunosuppressive therapies, often used in organ transplant recipients or for autoimmune conditions, can also broadly suppress antibody production, including IgA. Furthermore, chronic viral infections, such as human immunodeficiency virus (HIV) or Epstein-Barr virus (EBV), can directly or indirectly impair the immune cells responsible for IgA synthesis, leading to persistently low levels.
Temporary IgA Declines
Low IgA levels can be temporary, resolving over time. A common example is physiological hypogammaglobulinemia of infancy, where infants naturally have lower IgA levels during their first few months. This occurs because their immune system is still developing its own antibody production. During this period, infants often rely on maternal IgA received through breast milk for passive immunity.
As the infant’s immune system matures, usually by 6 to 12 months, their own IgA production typically increases to normal adult levels. Additionally, significant physiological stress or acute illnesses can sometimes lead to transient dips in IgA. For instance, a severe infection or intense physical or emotional stress might temporarily suppress the immune system’s antibody production. These temporary reductions usually resolve once the stressor is removed or the acute illness passes, and the immune system recovers its normal function.