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What is IgA Antibody?

gA Antibodies – The External Shield for Strong Immunity in Children The immune system plays a vital role in protecting young children from pathogens, especially during the early years when their immunity is still developing. Among the key components of the immune system are antibodies (Immunoglobulins). One of the most common and important antibodies in children is IgA, which acts as the first line of defense against illness.

What is IgA Antibody?

IgA (Immunoglobulin A) is one of five types of antibodies in the human body: IgG, IgM, IgA, IgE, and IgD. IgA is a surface antibody found in the skin and mucosal linings of the respiratory, digestive, and urogenital tracts, helping block the entry of pathogens (1). It is the most abundantly produced antibody daily, though its concentration in the blood ranks second after IgG (2). IgA exists in two forms: monomeric IgA circulating in the blood and dimeric secretory IgA (sIgA) found in mucosal secretions such as saliva, tears, mucus, and breast milk. sIgA is especially important for protecting mucosal surfaces, acting as a frontline defense against pathogens (2), (3).

IgA is produced by B lymphocytes – plasma cells (3). Interestingly, about 80% of antibody-producing cells are located in the gut mucosa, continuously generating IgA to protect the digestive tract – the body’s largest battleground against external pathogens (4). Thus, the child’s immune system, particularly in the gut, functions as an “IgA factory” to safeguard the body.

However, in infants and young children, IgA production is still limited due to immature immune development. It’s estimated that children only reach adult-like IgA levels around age six (5). During early life, breast milk serves as the primary source of IgA, providing essential immune support for the child’s developing system (6).

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How Does IgA Help Boost Children's Immunity?

IgA plays a crucial role in preventing infections and strengthening immunity. Here are the key reasons why IgA is vital for children’s immune health:

1. Protects Mucosal Surfaces from Pathogens

IgA acts as an “external shield” mainly present in the mucosal linings of the gut and respiratory tract—areas frequently exposed to harmful agents. It binds bacteria and viruses into antigen-antibody complexes, neutralizes them, and directs them to the body’s cleansing systems, preventing their entry (7). IgA works silently with mucus to neutralize pathogens without triggering inflammatory responses that damage tissues. It also helps maintain immune balance alongside a healthy microbiome (8).

2. Helps Prevent Respiratory and Digestive Infections

Young children are prone to respiratory and gastrointestinal infections due to underdeveloped immunity. Optimal IgA levels in target organs help reduce these risks. A review by M.H. Koenen in Clinical Immunology found that IgA deficiency is linked to recurrent respiratory and digestive infections in children (7). IgA in nasal secretions can deactivate viruses upon entry, while IgA in the gut helps block diarrhea-causing bacteria before they attack the intestinal lining.

3. Optimizes Gut Microbiota

The gut microbiome is essential for immune health. IgA regulates harmful bacteria and supports beneficial ones, promoting a balanced gut ecosystem that enhances digestive and immune function (9).

4. Reduces Risk of Allergies and Autoimmune Disorders

IgA binds and neutralizes allergens in food, preventing them from interacting with immune cells in the mucosa, thereby reducing allergic reactions (4). Breastfed children tend to have lower food allergy risks because IgA in breast milk coats foreign proteins, preventing excessive immune responses (10). In contrast, IgA-deficient individuals show higher rates of allergies and autoimmune diseases like asthma, allergic rhinitis, and celiac disease (2). This highlights IgA’s role in regulating immune responses and preventing the body from attacking harmless substances or its own healthy tissues.

5. Supports Passive Immunity Development

During infancy, when the immune system is still immature, breast milk-derived IgA is crucial for protection. Studies show that exclusively breastfed infants during the first six months have lower infection rates than formula-fed babies, thanks to high IgA levels and other immune-boosting factors in breast milk. Breastfed babies also experience fewer severe diarrhea episodes, respiratory infections, and allergies (11), (12). IgA is truly a “gift of immunity” from nature, delivered through breast milk to help children thrive in their early years.

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6. Sources of IgA Antibodies for Children

Breast milk is an excellent source of IgA for infants.
Colostrum, the first milk produced after birth, contains a high concentration of IgA—accounting for approximately 88% of total antibodies in breast milk (6). Scientific studies confirm that IgA is one of the most important “protective layers” that breast milk provides to newborns (6).

In addition to breast milk, several foods can help supplement and enhance IgA levels in children:

Bovine colostrum: Rich in antibodies such as IgA and IgG, bovine colostrum is a valuable source of immune support for children (13).

Probiotic-rich foods: Yogurt, live-culture yogurt, and other fermented dairy products contain beneficial bacteria like Bifidobacteria and Lactobacillus, which help balance gut microbiota and stimulate immune cells to produce secretory IgA (sIgA) (9).

Prebiotic-rich foods: Leafy greens, fruits, oats, legumes, and other fiber-rich foods contain prebiotics such as FOS, GOS, Inulin, and HMO. These compounds nourish beneficial bacteria, support a balanced gut microbiome, and promote the body’s natural production of IgA (14).

In certain cases—especially for children who are not exclusively breastfed or are in the “immune gap” phase—supplementing IgA through fortified milk and a well-balanced diet is essential.
To strengthen immunity and support overall development, parents should choose infant formula enriched with immune-boosting ingredients such as colostrum, prebiotics (HMO, GOS, FOS), probiotics (HMP), and whey protein rich in α-lactalbumin. In conclusion, IgA is a specialized antibody responsible for the first line of defense, primarily at mucosal surfaces. It acts as an “external shield” that traps and neutralizes pathogens before they penetrate deeper into the body. In children, this function is especially critical because mucosal surfaces are the main entry points for bacteria and viruses.

Ensuring children receive adequate IgA—through breast milk, proper nutrition, and a healthy lifestyle—helps strengthen their immune system, promoting better health and reducing the risk of illness during early childhood.

Reference

1. Ajay Patel, Ishwarlal Jialal. Biochemistry, Immunoglobulin A. May 1, 2023. StatPearls. Link

2. Yel L. Selective IgA deficiency. J Clin Immunol. 2010 Jan;30(1):10-6. Link

3. Humphrey, J.H., Perdue, S.S. (2025, May 1). immune system. Encyclopedia Britannica. Link

4. Berin MC. Mucosal antibodies in the regulation of tolerance and allergy to foods. Semin Immunopathol. 2012 Sep;34(5):633-42. Link

5. Weemaes, C., Klasen, I., Göertz, J., Beldhuis‐Valkis, M., Olafsson, O., & Haraldsson, A. (2003). Development of immunoglobulin A in infancy and childhood. Scandinavian Journal of Immunology, 58(6), 642-648. Link

6. Rio-Aige K, Azagra-Boronat I, Castell M, Selma-Royo M, Collado MC, Rodríguez-Lagunas MJ, Pérez-Cano FJ. The Breast Milk Immunoglobulinome. Nutrients. 2021 May 26;13(6):1810. Link

7. M.H. Koenen, J.M. van Montfrans, E.A.M. Sanders, D. Bogaert, L.M. Verhagen. Immunoglobulin A deficiency in children, an undervalued clinical issue. Clinical Immunology. 2019, 108293. Link

8. Cerutti A, Chen K, Chorny A. Immunoglobulin responses at the mucosal interface. Annu Rev Immunol. 2011;29:273-93. Link