IgA Application for Diagnosis: As a member of the first defense, immunoglobulin A (IgA) exerts a significant role in protecting from exogenous invasion and endogenous anomalies of the body. Beyond its essential role in mucosal immunity, abnormal IgA antibodies recently have been demonstrated to be associated with a variety of disorders, including autoimmune diseases, IgA nephropathy, celiac disease and Henoch-Schönlein purpura (HSP). All these critical roles and functions lay the foundation for the application of antibodies in diseases diagnosis.