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

Concept:

• Colostrum: The thick, yellowish-colored fluid secreted by the maternal mammary glands during the final stage of pregnancy and the initial days of lactation following parturition (childbirth).

• Biological Role: It acts as a concentrated source of nutrients and essential protective compounds, ensuring the transfer of passive immunity to the newborn infant whose active immune system is not yet fully developed.

• Antibodies (Immunoglobulins): These proteins identify and neutralize foreign agents. Secretory fluids in the human body are rich in specific classes of immunoglobulins.

Step 1: Analyze the distribution of immunoglobulin classes
There are five main classes of human immunoglobulins: IgA, IgD, IgE, IgG, and IgM.

• IgA: The primary antibody found in external secretions (such as tears, saliva, colostrum, and gastrointestinal secretions), offering mucosal immunity.

• IgG: The most abundant antibody in circulating blood plasma, which can cross the placental barrier.

• IgM: The first antibody produced during a primary immune response, primarily located in blood and lymph.

• IgD: Primarily functions as an antigen receptor on the surface of B lymphocytes.

Step 2: Relate the antibody type to colostrum
Since colostrum is a specialized maternal secretion, it contains highly concentrated levels of secretory IgA. This antibody coats the infant's intestinal tract, protecting against potential pathogens. This matches option (D).