1) As two or more Fc portions are required to stimulate effector functions so effector functions are carried out only by molecules with bound antigens and not with free Ig. 2) Fc region of the antibody molecules play a critical role in effector stimulation, so antibody isotypes varying in Fc region can be easily distinguished on the basis of interactions they carry. 3) Distribution of antibody molecules through different tissues is decided solely by the constant region in the heavy chain of an antibody molecule. This directed distribution through constant region of heavy chain is the reason behind IgA presence in mucosal secretions or recruitment of other antibodies to a particular tissue. 4) In antibody mediated immune response, variation in the isotypes of antibodies decides the ways to eliminate antigen from the body. In addition, isotype switching or class switching also has some role in it. e.g. antibody response to bacteria and viruses is carried out by IgG antibodies but switching to IgG isotype can also lengthen the humoral response because it has the longest half life period among all the antibodies. *Isotype- The presence of variations in the constant regions of the immunoglobulin heavy and light chains are called isotypes. Five heavy chain isotypes and two light chain isotypes are present in humans.