Incorporating an isotype control treated group is required to generate reliable data because it allows the researcher to accurately differentiate between results observed from primary antibody binding in an antigen-specific manner and results observed from non-antigen specific binding or other nonspecific effects of antibody injection.
Primary monoclonal antibodies administered to animals can interact non-antigen specifically with Fc receptors on cells, including B cells, dendritic cells, NK cells, macrophages, and more. Sometimes Fc receptor binding is involved in the primary antibodies’ mechanism of action, such as antibody directed cytotoxicity (ADCC). Nevertheless, non-antigen specific Fc receptor engagement can result in observable biological effects or phenotypes not related to antigen-specific binding. An isotype control antibody matching the isotype and subclass of the primary antibody will also bind to Fc receptors, allowing the researcher to control for those effects.
In addition to matching the isotype and subclass, an ideal isotype control must also match the host species of the primary antibody. Many primary monoclonal antibodies used for in vivo research in mouse models are created using hybridoma technology in rats or hamsters. When a xenogeneic rat or hamster IgG is injected into a mouse, an immune response may develop against the injected antibody. Multiple injections increase this possibility. As with Fc receptor binding, this can also result in observable phenotypes not related to antigen-specific binding. Including a group of mice treated with an isotype control antibody matching the host species of the primary antibody allows the researcher to control for these non-antigen specific effects.