What feature distinguishes IgG from other classes of antibodies in terms of immune response?

What feature distinguishes IgG from other classes of antibodies in terms of immune response?

• A. Involvement in allergic responses
• B. Ability to activate mast cells
• C. Ability to cross the placenta
• D. Production during primary response

Answer: (C)

The defining feature of IgG that sets it apart from other classes of antibodies is its ability to cross the placenta. This unique capability allows IgG to provide passive immunity to the fetus during pregnancy, transferring maternal antibodies that can protect the newborn from infections during the first few months of life.

IgG is the most abundant antibody in the bloodstream and plays a crucial role in the immune response by neutralizing toxins, opsonizing pathogens for phagocytosis, and activating complement. Its placental transfer is vital for giving the newborn immediate immune protection until its own immune system develops.

In contrast, other antibody classes do not share this property. For instance, IgE is primarily involved in allergic reactions and interacts with mast cells, but does not pass through the placenta. IgM is typically produced early in the primary immune response before IgG becomes prevalent, further differentiating its role and timing from that of IgG.