Which class of immunoglobulins provides passive immunity to the newborn?

Passive immunity is a type of immunity that is acquired by receiving pre-formed antibodies from another source, rather than through the body’s own immune response. This form of immunity is particularly important for newborns, who have limited immune systems and are vulnerable to infections. The class of immunoglobulins that provides passive immunity to the newborn is called IgG (immunoglobulin G).

IgG is the most abundant class of immunoglobulins in the human body and is responsible for providing long-lasting protection against a wide range of pathogens. During pregnancy, IgG antibodies are transferred from the mother to the fetus through the placenta, providing the newborn with a temporary form of immunity. This transfer of IgG is crucial in protecting the newborn from infections during the first few months of life, when their own immune system is still developing.

The transfer of IgG from mother to fetus occurs primarily during the last trimester of pregnancy. The placenta acts as a barrier that allows IgG antibodies to pass from the mother’s bloodstream into the fetus’s bloodstream. This transfer is facilitated by a specific receptor on the placental cells that binds to the Fc region of IgG antibodies. Once inside the fetus, these antibodies can bind to pathogens and neutralize them, preventing infection.

In addition to the transfer of IgG through the placenta, some IgG antibodies can also be transferred to the newborn through breast milk. Breast milk contains high levels of IgG antibodies, which can help protect the newborn from infections even after they are born. This transfer of IgG through breast milk is another important source of passive immunity for the newborn.

However, it is important to note that the passive immunity provided by IgG is temporary. The levels of IgG antibodies in the newborn’s bloodstream gradually decrease over time, and by the time the child is about 6 months old, the levels of IgG antibodies are typically low enough that the child is no longer protected by passive immunity. At this point, the child’s own immune system begins to mature, and they start producing their own antibodies in response to infections.

In conclusion, IgG is the class of immunoglobulins that provides passive immunity to the newborn. This transfer of IgG from the mother to the fetus and through breast milk is crucial in protecting the newborn from infections during the early stages of life. However, it is important for parents to ensure that their children receive appropriate vaccinations as they grow older to build their own immune systems and maintain long-term protection against various pathogens.