Immune Responses, Immunisation, and Immunity in Pregnancy
With Sophie and Marcus, Biology & Physiology Specialist
Key Takeaways
- The innate system responds quickly but generically.
- The adaptive system takes longer but is highly specific — targeting particular antigens using B and T lymphocytes.
- An antigen is any molecule recognised as foreign — usually a protein on a pathogen's surface.
- Antibodies produced by B cells are precisely shaped to bind one antigen.
- IgG is most significant — it is the only class that crosses the placenta, giving the fetus passive immunity.
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Full Transcript
Sophie: This episode covers immune responses, immunisation, and immunity in pregnancy. I'm Sophie, and with me is Marcus, our Biology and Physiology Specialist. Marcus, how does the adaptive immune system differ from innate immunity?
Marcus: The innate system responds quickly but generically. The adaptive system takes longer but is highly specific — targeting particular antigens using B and T lymphocytes. Crucially, it forms memory so the second encounter with the same antigen produces a faster, stronger response.
Sophie: Can you explain antigen-antibody interactions simply?
Marcus: An antigen is any molecule recognised as foreign — usually a protein on a pathogen's surface. Antibodies produced by B cells are precisely shaped to bind one antigen. That binding neutralises the pathogen or flags it for destruction.
Sophie: What antibody classes matter most in pregnancy?
How does immune responses, immunisation, and immunity in pregnancy work in a healthcare context?
Marcus: IgG is most significant — it is the only class that crosses the placenta, giving the fetus passive immunity. IgA in breast milk protects the neonatal gut. IgM is produced first in any new infection, so its presence suggests recent exposure.
Sophie: How long does passive IgG protection last for the newborn?
Marcus: Maternal IgG wanes over the first three to six months as it is catabolised. That is why neonatal immunisation starts early — to build the baby's own active immunity before maternal protection disappears.
Sophie: How does pregnancy alter immune function and why does that matter?
Marcus: Pregnancy involves immune modulation to tolerate the semi-foreign fetus. Th1 responses — which fight intracellular pathogens — are relatively suppressed, making pregnant women more susceptible to listeria, influenza, and varicella.
What should learners understand about immune responses, immunisation, and immunity in pregnancy?
Sophie: What vaccinations are recommended in pregnancy and why?
Marcus: Influenza and pertussis vaccines are offered to all pregnant women. Influenza severity is higher in pregnancy. Pertussis antibodies cross the placenta to protect the newborn before they can be vaccinated themselves.
Sophie: Understanding the science deepens the conversation. Thank you, Marcus.
Marcus: Those conversations save lives — for both the woman and her baby. That is why this knowledge matters so much in midwifery.