Which of the following immunoglobulins cross the placenta?
A.
IgM
B.
IgA
C.
IgG
D.
IgE
The Correct answer and Explanation is:
The correct answer is C. IgG.
Explanation:
Immunoglobulins, or antibodies, play a crucial role in the body’s immune response, helping to protect against infections. There are five major types of immunoglobulins, namely IgG, IgM, IgA, IgE, and IgD. Among these, IgG is the only one that can cross the placenta, providing passive immunity to the fetus.
IgG:
IgG is the most abundant immunoglobulin in the human body, accounting for about 75-80% of the total antibodies in the bloodstream. It has the unique ability to cross the placental barrier from the maternal bloodstream to the fetus. This transfer begins around the second trimester and continues until birth. The process is mediated by specialized receptors in the placenta known as Fc receptors, which specifically bind to the Fc region of IgG molecules. This transfer provides the fetus with passive immunity, helping to protect the newborn from various infections for the first few months of life, as their immune system is still developing.
Other Immunoglobulins:
- IgM: This is the first antibody produced in response to an infection. Although it plays a crucial role in primary immune responses, it is too large to cross the placental barrier because of its pentameric structure.
- IgA: Primarily found in mucosal areas like the respiratory and gastrointestinal tracts, IgA provides protection at these surfaces. It is also present in breast milk and contributes to protecting the newborn postnatally, but it does not cross the placenta.
- IgE: This antibody is associated with allergic reactions and parasitic infections. Like IgM and IgA, IgE cannot cross the placenta.
Therefore, IgG is the only immunoglobulin that can pass through the placenta, ensuring that the fetus receives maternal antibodies that provide early protection from pathogens during the first few months of life.