Antibodies are classified into five different types based on their structure and function. These types are Immunoglobin M (IgM), Immunoglobin D (IgD), Immunoglobin G (IgG), Immunoglobin A (IgA), and Immunoglobin E (IgE). IgG is the most abundant antibody and accounts for 10-20% of plasma proteins and 70-75% of the total immunoglobulins in plasma. IgG is further classified into subclasses based on their abundance in the body, which include IgG1, IgG2, IgG3, and IgG4. These subclasses differ in their primary amino acid sequences and structural differences in the hinge and heavy chain constant regions.