A Case of Type 2 Diabetes Mellitus Revealed Transient Positivity of Glutamic Acid Decarboxylase (GAD) Antibodies Following Immunoglobulin Administrations.

Glutamic acid decarboxylase (GAD) antibodies are frequently measured in diabetes care as islet-associated autoantibodies that are useful in the diagnosis of type 1 diabetes. However, GAD antibodies derived from other persons may contaminate immunoglobulin preparations, and there have been cases of transiently positive GAD antibodies after intravenous immunoglobulin (IVIg) in patients who were originally negative for GAD antibodies. Clinicians may be unaware of such contamination and misdiagnose some cases as type 1 instead of type 2 diabetes mellitus based on positivity for GAD antibodies. Herein, we present a case of type 2 diabetes mellitus that revealed transiently positive GAD antibodies following immunoglobulin administrations. A 68-year-old woman with a medical history of diabetes mellitus was admitted to our hospital for the treatment of Guillain-Barré syndrome, and IVIg was started on the day of admission. Blood tests on admission revealed negative for GAD antibodies but showed weak positivity on day one after IVIg. Afterward, GAD antibodies turned negative on day 72. Immunoglobulin preparations were revealed to have a high concentration of GAD antibodies. Based on changes in GAD antibody titers and all negativity for anti-insulinoma-associated antigen-2 (IA-2), insulin, and zinc transporter 8 (ZnT8) antibodies, the patient was diagnosed with type 2 diabetes mellitus rather than slowly progressive type 1 diabetes mellitus (SPIDDM). This case demonstrates that it is important for the medical clinician to be aware of the possible presence of GAD antibodies in immunoglobulin preparations and to measure antibody titers before and after their use for diagnosing the type of diabetes mellitus.

Immunoprecipitation with an Anti-Epitope Tag Affinity Gel to Study Protein-Protein Interactions.

Protein-protein interactions (PPIs) play a pivotal role in biological phenomena, such as cellular organization, intracellular signal transduction, and transcriptional regulation. Therefore, understanding PPIs is an important starting point for further investigation of the function of the target protein. In this study, we propose a simple method to determine the binding of two target proteins by introducing mammalian expression vectors into HEK-293 cells using the polyethylenimine method, lysing the cells in homemade protein lysis buffer, and pulling down the target proteins on an epitope tag affinity gel. In addition, the PPI between the various epitope tag fused proteins can be confirmed by using affinity antibodies against each tag instead of the epitope tag affinity gel. This protocol could also be used to verify various PPIs, including nuclear extracts, from other cell lines. Therefore, it can be used as a basic method in a variety of PPI experiments. Proteins degrade by extended time course and repeated freeze-thaw cycles. Therefore, cell lysis, immunoprecipitation, and immunoblotting should be performed as seamlessly as possible.