International Board of Certified Lactation Consultant (IBCLC) Practice Exam

What is the main immunoglobulin found in breast milk?

1. IgG

2. IgM

3. IgA

4. IgD

The correct answer is: IgA

The main immunoglobulin found in breast milk is immunoglobulin A (IgA). This antibody plays a crucial role in the immune protection of infants, particularly in their gastrointestinal tract. When infants consume breast milk, they receive IgA, which can help to form a protective mucosal barrier in their intestines, preventing pathogens from entering their system and contributing to their overall immune defense. IgA is particularly effective because it exists in a form known as secretory IgA (sIgA) when in breast milk. This form is resistant to degradation by stomach acids and digestive enzymes, allowing it to reach the intestinal tract effectively. The presence of sIgA in breast milk is especially beneficial during the early stages of life when an infant's immune system is still developing and they are at a higher risk for infections. In contrast, while IgG, IgM, and IgD are important immunoglobulins in other aspects of the immune response, they do not dominate the immunological composition of breast milk in the same way IgA does. IgG is the most prevalent antibody in the bloodstream and provides systemic immune protection, but it is present in much lower amounts in breast milk compared to IgA.