Used as a negative control in immunoassays to distinguish specific antibody binding from non-specific background signals. Commonly applied in flow cytometry, immunohistochemistry, and ELISA to validate the specificity of primary antibodies. Helps ensure that observed results are due to antigen-antibody interactions rather than Fc receptor binding or assay artifacts. Suitable for experiments involving IgG1 kappa isotype detection in human or humanized antibody studies.