What function do IgG antibodies serve in the human body?

IgG antibodies play a crucial role in the immune response, one of their primary functions being the activation of the classical complement pathway. This pathway is part of the innate immune system and is critical for the opsonization of pathogens, leading to their destruction. When IgG antibodies bind to an antigen on the surface of a pathogen, they can initiate a cascade of proteins in the complement system that enhances the immune response. This includes promoting inflammation, attracting immune cells to the site of infection, and directly lysing pathogens.

The other answer choices, while they describe important aspects of the immune system or potential functions of different antibody classes, do not accurately reflect the specific role of IgG antibodies. Activating mast cell degranulation is more closely associated with IgE antibodies, which are involved in allergic responses. The prevention of respiratory tract infections could refer to various antibodies in different contexts, but IgG's distinct role in complement activation differentiates it from these more general functions.