ASCP Specialist in Blood Banking (SBB) Practice Exam 2025 – Your All-in-One Guide to Exam Success!

The correct answer is based on the complement activation capabilities of different immunoglobulin G (IgG) subclasses. IgG1 and IgG3 are the subclasses that are particularly effective at activating the classical complement pathway.

IgG1 is the most abundant IgG subclass in serum and is known for its ability to bind to Fc receptors on phagocytes and other immune cells, facilitating opsonization and promoting the clearance of pathogens. It has a strong ability to activate complement due to its structure, which allows it to efficiently interact with C1q, the first component of the classical pathway.

IgG3, while less abundant than IgG1, is even more potent in activating complement. Its longer hinge region provides greater flexibility and allows for multiple binding sites, leading to a stronger interaction with C1q. This enhancement of complement activation is crucial in the immune response, particularly against infections.

Together, IgG1 and IgG3 activate complement effectively, leading to opsonization and lysis of pathogens. This is why the choice highlighting these two subclasses is the most accurate regarding their roles in complement activation.