International Board of Certified Lactation Consultant (IBCLC) Practice Exam

Which immunoglobulin is predominantly found in human milk?

1. IgG

2. IgM

3. IgA

4. IgE

The correct answer is: IgA

The predominant immunoglobulin found in human milk is immunoglobulin A (IgA). This is particularly critical for newborns, as it plays a vital role in mucosal immunity. IgA prevents pathogens from attaching to the mucosal surfaces in the gastrointestinal tract, respiratory system, and urogenital tract, effectively providing a protective barrier during the early stages of life when infants are particularly vulnerable to infections. In addition to its protective functions, IgA in human milk is specifically secretory IgA (SIgA). This form is dimeric and more resistant to enzymatic degradation, which enhances its protective properties as it passes through the digestive system of the infant, ensuring that it can function effectively in its immunological role. The other immunoglobulins listed, such as IgG, which is the most abundant antibody in the blood and provides systemic immunity, and IgM, which is associated with the first response to infection, are present in lower concentrations in breast milk compared to IgA. IgE is involved in allergic responses and is not a significant component of human milk. Thus, IgA's predominant presence in breast milk underlines its importance in infant health and immunological defense.