Question

Colostrum, secreted by mother during initial days of lactation, is abundant in

• A. IgD
• B. IgG
• C. IgM
• D. IgA

Hint:

• Passive vs. Active Immunity: Colostrum provides passive immunity because pre-formed antibodies (IgA) are transferred to the host, rather than the infant's body producing them.

• Placental antibody: Remember that IgG is the only antibody class capable of passing through the human placenta to provide prenatal protection.

Answer 1

The Correct Option is D

Step 1: Recall what colostrum is.
Colostrum is the thick yellowish fluid the mother secretes in the first few days of lactation after childbirth.
Step 2: Note its role.
It gives the newborn passive immunity along with rich nutrition, because the baby's own immune system is not yet fully developed.
Step 3: List the antibody classes.
The five classes are IgA, IgD, IgE, IgG and IgM, each with its own distribution and job.
Step 4: Match secretions to IgA.
IgA is the main antibody in external secretions like tears, saliva, and colostrum, providing mucosal protection.
Step 5: Rule out the others.
IgG is most abundant in plasma and crosses the placenta, IgM is the first in a primary response, and IgD acts as a receptor on B cells. None of these is the main one in colostrum.
Step 6: Conclude.
Colostrum is abundant in IgA, which coats the infant's gut and protects it from pathogens.
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