Final answer:
The IgG subclasses are ranked from most to least abundant as IgG1, IgG2, IgG3, and IgG4; with IgG1 and IgG3 being particularly important in immune defense mechanisms.
Step-by-step explanation:
IgG Subclasses Proportions
The four IgG subclasses ranked in descending order of their respective proportions of total IgG (from highest to lowest percentage) are IgG1, IgG2, IgG3, and IgG4. IgG is the most abundant type of antibody found in the blood circulation, making up about 80% of all antibodies. The IgG subclasses differ slightly in their biological properties but all serve important roles in the body's immune response. IgG1 is the most prevalent, followed by IgG2, IgG3, and then IgG4. These subclasses are important for various immune functions including virus and bacteria neutralization, opsonization, which promotes phagocytosis, and activating complement pathways. Furthermore, IgG1 and IgG3 are usually considered the most important for defense against pathogens because they have the greatest ability to activate complement and bind to Fc receptors on immune cells.