Therapeutic modalities such as antibodies and fragment crystallizable (Fc)-fusion molecules are often engineered with a specific immunoglobulin G (IgG) isotype and subtype in order to impart particular functionalities, such as half-life extension or induction of cytotoxic activity. Alternatively, a specific isotype and subtype may be selected to mitigate, or lessen, potential induction of unwanted biological activities. These modalities have defined structure/function domains that impart the therapeutic benefit.