Q.Colostrum secreted by the mother's mammary glands in a human female during the initial days of lactation is rich in antibody : (A) IgE (B) IgD (C) IgA (D) IgG

Concept: Colostrum provides passive immunity to the newborn via secretory antibodies.

Reasoning:

1. Colostrum is the first milk secreted in the initial days after childbirth. It is specially rich in antibodies that protect the infant's gut and respiratory tract. …

The Concept: Passive Immunity via Colostrum

When a baby is born, its own immune system is still immature. It cannot yet produce enough antibodies to fight off the many pathogens it will encounter. Nature’s solution is passive immunity — the transfer of ready-made antibodies from mother to child.

This happens in two ways:

• Across the placenta (before birth): IgG antibodies cross from the mother’s blood into the fetal circulation.
• Through breast milk (after birth): The first milk, called colostrum, is especially rich in a different antibody — IgA.

Why IgA? Because the newborn’s biggest threat is from pathogens that enter through the mouth, nose, and gut. IgA is uniquely suited to protect these mucosal surfaces. In colostrum, it exists as secretory IgA (sIgA) , which is resistant to digestion and can coat the baby’s gut lining, neutralising bacteria and viruses before they cause infection.

Step-by-Step Reasoning

1. Identify the unique antibody in colostrum.

   Colostrum is yellowish, thick, and produced for the first 2–4 days after birth. It is specifically known for its high concentration of IgA (up to 5–15 g/L), far more than in mature milk. This IgA is secreted by plasma cells in the mammary gland and is transported into the milk as secretory IgA.

2. Eliminate the other options based on their roles.

   • (A) IgE: Involved in allergic reactions and defence against parasites. Not a major component of colostrum.
   • (B) IgD: Functions mainly as a receptor on B cells. Very low concentration in secretions. …