Rapid Isotyping of Mouse Monoclonal Antibodies

Determination of class and subclass of monoclonal antibodies (MAbs) is important because several immunochemical and functional properties of antibodies depend on the isotype. Knowledge of the light-chain isotype (κ for 95% or λ for 5% of mouse antibodies) has limited practical value. In contrast, the heavy-chain isotype is very informative (see Table 1 ); protein A or protein G binding, euglobulin properties, complement binding, kinetics of digestion with papain or pepsin, clearance from serum, valence, and avidity, all depend on isotype. Isotyping is a basis for the selection of antibody purification, conjugation, fragmentation, and storage procedures, and predicts cytotoxic properties and half-life in vivo (see Note 1 ). In addition, isotyping is useful to control lot to lot consistency, detect contamination by another antibody, and identify hybridoma switch variants (see Notes 2 –8 for further comment on applications). Table 1  Isotype-Dependent Properties of Monoclonal Antibodies

a EP = Euglobulin precipitation, GF = gel filtration, IEC = ion-exchange chromatography, PA = protein A affinity chromatography; and PG = protein G affinity chromatography. b Frequent anticarbohydrate; isotype. Precipitates at low-salt concentrations (euglobulin). Stability increased at high-salt molarity. c Frequent isotype after short immunization protocols. Precipitates at low-salt concentration (euglobulin). Stability increased at high-salt molarity.