There are five types of antibodies IgG, IgA, IgM, IgD, and IgE. IgG is the most abundant antibody-forming 80% of the total antibodies. It is the only antibody that can pass through the placenta. It is formed in the secondary immune response. It has a structure of a typical antibody having 4 peptides arranged in a Y shape manner. IgM is the largest in size (5 times greater than IgG). It is formed in the primary immune response. It is a pentamer having 5 such Y shaped structures.