Inclusion of an appropriate isotype control is essential for the proper interpretation of experimental results. Because isotype control antibodies have no relevant specificity, they enable the researcher to distinguish non-specific "background" binding from antigen-specific antibody binding. Non-specific binding of primary antibodies may occur due to either binding of antibody to Fc receptors or non-specific interactions with cellular proteins, lipids, or carbohydrates. Additionally, autofluorescence or endogenous enzyme activity in target cells may give a false positive that could be misinterpreted as antibody binding. These factors vary by target cell type and the isotype of the primary antibody. Therefore, the primary antibody used should be matched to an isotype control of identical species and isotype (including both heavy and light chains).