Colostrum, the yellowish fluid, secreted by the mother during the initial days of lactation is very essential to impart immunity to newborn infants because it contains?

The correct option is D

Immunoglobulin A

The correct option is D.

The explanation for the correct option:

• Colostrum is the light yellow colored fluid that is secreted by the mother after the birth of the baby and on the initial days of lactation. This is very essential for a newborn as it supplies plentiful immunoglobulin A (IgA) that provides immunity.
• It is an example of naturally acquired immunity. It is essential because the immune system of newborns is not developed and immunity acquired from colostrum provides protection.

The explanation for incorrect options:

Option A:

• Natural killer cells are one kind of cytotoxic lymphocyte cell and have a critical role in the innate immune system for combatting infectious pathogens.
• They are mainly involved in the antiviral and anti-tumor response. NK-cells are not present in colostrum.

Option B:

• Monocytes are white blood cells (lymphocytes). Their function is to find and destroy pathogenic viruses, bacteria, fungi, and protozoa.
• Monocytes bring other WBCs to help in treating injury and preventing infections. They are part of cell-mediated immunity.

Option C:

• Macrophages are antigen-presenting cells (APCs) and have an essential role in the detection, phagocytosis, and destruction of pathogenic bacteria and other organisms.
• Their function is to present antigens to T-cells and start off inflammation by activating the secretion of cytokines that activate other immune cells. They are part of cell-mediated immunity.

Final answer: So, colostrum, the light yellow colored fluid, secreted by the mother during the initial days of lactation is very essential to impart immunity to newborn infants because it contains abundant immunoglobulin A (IgA).