originally, either of two identical fragments, each containing an antigen combining site, obtained by papain cleavage of molecules of the IgG class of immunoglobulins . The term is now generally used as an adjective in compound terms such as fragment and region, referring to an “arm” of any immunoglobulin monomer, which consists of one light chain and the adjoining heavy chain . digoxin immune (ovine) a preparation of antigen-binding fragments derived from specific antidigoxin antibodies produced in sheep that have been immunized with digoxin coupled as a hapten to human serum albumin, used as an antidote to life-threatening digoxin and digitoxin overdose; administered intravenously.