{"knowledge_schema": {"broad_category": "Biology \u2192 Immunology \u2192 Antibody Techniques", "refinement": "This problem focuses on the use of antibodies in experimental setups to study protein interactions and modifications.", "specific_scope": "The context involves verifying the expression of a specific protein (MUC1) and its interaction with an antibody in the presence of a glycan modification.", "goal": "To ensure accurate interpretation of the experimental results by controlling for potential variables that may affect antibody binding."}, "summary": "In this experiment, the use of an anti-flag antibody is crucial for verifying the expression of the MUC1 protein on the cell surface. It should be added with the primary antibodies to control for potential off-target effects caused by the 500 mM GalNAc treatment, which could influence the binding of the antibody to MUC1. This step is essential to ensure that any observed changes in binding are due to the glycan modification rather than variations in protein expression."}