Jenny O'Mara was five months pregnant when she stepped on a rusty piece of scrap metal while hauling rotted wood from a dilapidated shed in her garden. The sliver of metal cut through her sneaker and pierced her heel deeply

Question

Her physician gave her a tetanus booster. When Jenny's baby was born she decided to breastfeed. If the baby's antibodies were tested for specificity to tetanus 2 months after birth, what would be the expected finding?
a. the presence of anti-tetanus toxoid IgA antibodies
b. the presence of anti-tetanus toxoid IgM antibodies
c. the presence of anti-tetanus toxoid IgG antibodies
d. the presence of IgM antibody specific for Clostridium tetani cell-wall components
e. the presence of IgG antibody specific for Clostridium tetani cell-wall components.

Answer 1

Rationale: The correct answer is c. This is a case of passive immunity provided to the fetus during pregnancy through transplacental transfer of IgG. Only IgG antibodies cross the placenta, with the aid of FcRn, and enter the fetal circulation during pregnancy, providing passive immunity for the newborn for the first 3–6 months, after which antibody levels diminish as a result of catabolism, and IgG must then be made by the infant. The antibody specificity will be against the tetanus toxoid, not cell-wall entities, because the booster vaccine is a subunit vaccine made of toxoid from Clostridium tetani, not whole bacterial cells. Sophie will make IgG anti-toxoid antibodies, not IgA, because of the route of immunization; intramuscular injection would stimulate the production of IgG antibodies. IgA antibody production would require mucosal delivery. Therefore, even though the newborn is breastfeeding and passively receiving IgA antibodies from Sophie, the IgA antibodies will not have specificity for tetanus toxoid.