Question

Why can infants born without an immune system survive for the first few months of their lives with no apparent problems? a. Limited antibodies are produced by bacteria in the infant’s colon. b. The exposure to pathogens during this time is lim- ited. c. Antibodies are passively received from the mother through the placenta and breast milk. d. The fetal thymus produced a limited number of antibodies during the eighth and ninth months of pregnancy.

Short answer

c. Antibodies are passively received from the mother through the placenta and breast milk.

Step-by-step solution

Understanding the problem

Analyze why infants born without an immune system can survive during the first few months without apparent problems. Consider the contributions mentioned in the options.

Analyze Option A

Check if the statement 'Limited antibodies are produced by bacteria in the infant’s colon' is correct. Note that antibodies are proteins produced by specific immune cells, not bacteria.

Analyze Option B

Examine if 'The exposure to pathogens during this time is limited' can be a reason. Realize that while exposure may be somewhat limited, it's not the primary reason for survival without an immune system.

Analyze Option C

Verify if 'Antibodies are passively received from the mother through the placenta and breast milk' is the correct reason. Understand that maternal antibodies provide passive immunity to the infant.

Analyze Option D

Evaluate if 'The fetal thymus produced a limited number of antibodies during the eighth and ninth months of pregnancy' is correct. Note that the thymus is involved in the maturation of T-cells, not antibody production.

Conclusion

Summarize the analysis and choose the best option. From steps 2 to 5, conclude that the primary reason for infants' survival is the passive transfer of maternal antibodies through the placenta and breast milk.

Key concepts

Passive Immunity

Passive immunity is a type of immunity where a person gains immediate protection against pathogens via transferred antibodies, rather than by their own immune system producing them. This transfer can occur through different ways, such as injections of antibody-containing serum or through natural processes like during pregnancy and breastfeeding.
For infants born without a fully developed immune system, passive immunity provides essential protection. The maternal antibodies passed to the infant through the placenta during pregnancy and later through breast milk help fend off infections and diseases during their early months. This passive immunity is crucial for infant survival as it compensates for their immature immune response systems.

Maternal Antibodies

Maternal antibodies are the antibodies that a mother passes to her baby during pregnancy and through breastfeeding. These antibodies are a critical form of passive immunity.
The two primary ways maternal antibodies are transferred include:

• Through the placenta: During the last trimester of pregnancy, immunoglobulin G (IgG) antibodies cross the placenta from mother to fetus. This transfer helps the baby get immediate protection against various pathogens.
• Through breast milk: After birth, the mother’s milk, especially the colostrum (the first milk produced), is rich in antibodies. Immunoglobulin A (IgA) in breast milk protects infants from gastrointestinal infections by lining their gut.

These maternal antibodies provide a temporary shield to infants until their own immune system becomes more developed and capable of producing its own antibodies.

Infant Survival

Infant survival in the first few months, especially for those with undeveloped immune systems, heavily depends on the immunity transferred from their mothers. Despite lacking a fully developed immune system, infants are typically protected from many infections due to the combination of maternal antibodies.
Without this passive immunity, newborns would be much more susceptible to diseases and infections. The first few months are crucial as the infant's own immune system gradually matures and starts producing its own antibodies. This period is a window of vulnerability that is effectively managed by the passive immunity provided by the mother.
Understanding the role of maternal antibodies and passive immunity underscores the importance of maternal health and breastfeeding, as these factors directly impact infant health and survival during the early stages of life.