Basic Science for the Clinician 58: IgG SubclassesSigal, Leonard H. MD, FACP, FACRJCR: Journal of Clinical Rheumatology: September 2012 - Volume 18 - Issue 6 - p 316–318 doi: 10.1097/RHU.0b013e318269446b Basic Science for the Clinician Abstract Author Information In evolutionary terms, IgG is the most recent addition to the human humoral immune response, the most recent of the 5 isotypes (classes). The IgG 4 subclasses and their multiple receptors, each with a unique structure and functions, speak to their broad repertoire of often overlapping functions. The IgG subclasses differ only slightly in structure, but therein lies their unique qualities. Focusing solely on the clinical niches filled by each and the clinical correlations thereof allows one to clearly see nature in its abhorrence of, and skill in filling, vacuums. One of the IgG subclasses, IgG4, the least in serum concentration, has recently become the topic of intense interest, as the linkage of certain diseases with IgG4 becomes apparent. As this association is studied, the molecular biology at the root of these diseases becomes the predominant cytokines explaining the pattern of histopathology. From the Division of Rheumatology and Connective Tissue Research, Departments of Medicine, Pediatrics, and Molecular Genetics & Microbiology, University of Medicine and Dentistry of New Jersey – Robert Wood Johnson Medical School, New Brunswick, NJ. The author declares no conflict of interest. Correspondence: Leonard H. Sigal, MD, FACP, FACR, MEB 484, Division of Rheumatology, Department of Medicine, UMDNJ – Robert Wood Johnson Medical School, 1 R W Johnson Pl, New Brunswick, NJ 08903-001. E-mail: email@example.com. © 2012 Lippincott Williams & Wilkins, Inc.