Q.(a) Name and state the type of immunity that acts as a ‘biological shield’ to the developing foetus against many infections in the mother’s womb.

1. The type of immunity that acts as a ‘biological shield’ to the developing foetus is natural passive immunity. This immunity is conferred by the transfer of antibodies, primarily IgG, from the mother to the foetus across the placenta.
2. A large proportion of infants remain free from potent infections for several months after birth due to two primary reasons:

• The antibodies (IgG) received from the mother through the placenta during gestation persist in the infant's system, providing protection for a period post-birth. …

Our immune system is a remarkable defence mechanism, constantly working to protect us from a myriad of pathogens. Immunity can be broadly categorised into innate (non-specific) and acquired (specific) immunity. Within acquired immunity, we further distinguish between active and passive forms. Active immunity develops when an individual's own body produces antibodies in response to an infection or vaccination. Passive immunity, on the other hand, involves the direct transfer of pre-formed antibodies from one individual to another. This latter type is particularly vital in the context of a developing foetus and a newborn infant, who are not yet capable of mounting a robust immune response of their own.

1. The type of immunity that acts as a ‘biological shield’ to the developing foetus against many infections in the mother’s womb is passive immunity. More specifically, it is a form of natural passive immunity. During pregnancy, the mother's body actively transfers antibodies to the developing foetus through the placenta. The primary antibody responsible for this crucial protection is Immunoglobulin G (IgG). IgG antibodies are small enough to cross the placental barrier, entering the foetal bloodstream. This transfer equips the foetus with a ready-made defence system, protecting it from various pathogens to which the mother has immunity. This pre-emptive defence is what effectively functions as a 'biological shield', safeguarding the vulnerable foetus from infections that the mother might encounter.
   Important

   The transfer of IgG antibodies from mother to foetus across the placenta is a key mechanism of natural passive immunity, providing essential protection before birth.

2. A large proportion of infants remain free from potent infections for at least three months after birth, or even longer if breastfed, due to a continuation of this passive immunity, supplemented significantly by maternal antibodies received post-natally. There are two primary reasons for this sustained protection:

• Persistence of Maternal Antibodies: The IgG antibodies transferred from the mother across the placenta during pregnancy do not immediately disappear after birth. They persist in the infant's circulatory system for several weeks to months, continuing to provide protection against a range of infections. This initial reservoir of maternal antibodies gives the infant a critical window of protection while its own immune system is still maturing and learning to produce its own antibodies.
• Role of Breastfeeding (Colostrum and Milk): Breastfeeding plays an exceptionally vital role in bolstering the infant's immunity.
  • Colostrum: The yellowish fluid secreted by the mother during the initial days of lactation (the first few days after birth) is known as colostrum. It is incredibly rich in antibodies, particularly Immunoglobulin A (IgA). …