An isotype control is an antibody selected as a negative control to detect non-specific binding in antibody-based experiments.
Understanding antibody structure is important for understanding how to choose an isotype control. Antibodies (immunoglobulins, Ig) are composed of two heavy chains and two light chains. In humans, there are five heavy chain isotypes α,δ,γ,ε,μ, corresponding to five antibody isotypes: α (IgA), δ (IgD), ε (IgE), γ (IgG), and μ (IgM).
In addition to the heavy chains, an antibody has one of two light chain isotypes, κ and λ, that may also play a role in the physicochemical properties of antibodies (Figure 1; references 1, 2).