Final answer:
The correct match is IgA: found in secretions such as colostrum, tears, and mucus. It is crucial for mucosal immunity and is present in bodily secretions like breast milk, playing a pivotal role in protecting infants.
Step-by-step explanation:
The correct match among the options provided is IgA: found in secretions such as colostrum, tears, and mucus. IgA exists as a dimeric molecule in secretions and plays a crucial role in mucosal immunity by being present in fluids such as breast milk (colostrum), saliva, and tears.
The IgA in these secretions can protect the extensive mucosa and confer passive immunity to an infant through breastfeeding. IgG, not IgM as mentioned, is the class of antibody that readily crosses the placenta to provide protection to the fetus/newborn.
IgM, which is typically structured as a pentamer, is the first immunoglobulin produced in a primary immune response. Finally, IgE is not structured as a pentamer, but is the antibody that binds to mast cells causing antigen-specific degranulation during allergic responses.