stepsfacts on Instagram: "Immunoglobulin G (IgG) is the most abundant antibody in human serum, playing a crucial role in the adaptive immune response. It is produced by plasma cells and provides long-term immunity by neutralizing pathogens, promoting phagocytosis, and activating the complement system. IgG is unique in its ability to cross the placenta, offering passive immunity to newborns. It is subdivided into four subclasses (IgG1, IgG2, IgG3, and IgG4), each with distinct functional properti