Isotype Controls: Isotype controls are a type of negative control designed to measure the level of non-specific background signal caused by primary antibodies, based upon the tissue type of the sample. Non-specific binding of primary antibodies are typically caused by the following reasons: ? Non-specific Fc receptor binding to cells ? Non-specific antibody interactions with cellular proteins or fluorochromes ? Non-specific binding of the antibody or fluorochromes to cellular components ? Cell autofluorescence Usually, the background signal is the result of immunoglobulins binding non-specifically to Fc receptors present on the cell surface. For example, antibodies raised in mice, particularly those of the IgG2a isotype, will bind strongly to some human leukocytes regardless of the test antibody specificity. In this case you would need a mouse IgG2a isotype control for use with human cells or tissues. Isotype controls are most commonly used in flow cytometry experiments, but may also b