An isotype control is a type of control used in immunohistochemistry (IHC) and flow cytometry experiments to differentiate non-specific background signal from specific antibody signal. This control uses an antibody that matches the isotype, species, and conjugation of the primary antibody but lacks specificity for the target antigen. Essentially, it helps to ensure that the observed staining is due to the specific binding of the primary antibody to the antigen and not due to non-specific binding or other factors.
