Systemic disorders with rheumatic manifestations: Edited by John Stone and Arezou KhosroshahiWhat is IgG4? A review of the biology of a unique immunoglobulin subtypeNirula, Ajaya; Glaser, Scott Ma; Kalled, Susan Lb; Taylora, Frederick Rb Author Information aBiogen Idec, 5200 Research Place, San Diego, California, USA bBiogen Idec, 14 Cambridge Center, Cambridge, Massachusetts, USA Correspondence to Ajay Nirula, Biogen Idec, 5200 Research Place, San Diego, CA 92130, USA Tel: +1 858 436 4906; fax: +1 858 795 9640; e-mail: [email protected] Current Opinion in Rheumatology: January 2011 - Volume 23 - Issue 1 - p 119-124 doi: 10.1097/BOR.0b013e3283412fd4 Buy Erratum Metrics Abstract Purpose of review Recent descriptions of the group of clinical disorders collectively defined as IgG4-related systemic disease (IgG4-RSD) have prompted this review of the unique biology of the IgG4 antibody. This article will discuss IgG4 structure and function, the unique phenomenon of half-antibody exchange, and the implications of IgG4 biology for its proposed role in immunologic diseases. Recent findings IgG4 antibodies have unique structural and functional properties and undergo ‘half-antibody exchange’ in vivo, resulting in recombined antibodies composed of two different binding specificities. The production of IgG4 antibodies appears to be driven in part by T helper 2 (Th2) cytokines that mediate allergic responses and IgE production. Although serum IgG4 levels in healthy individuals vary significantly, data from multiple sclerosis (MS) patients suggest tight regulation of individual IgG4 levels over time. IgG4-RSD represents a diverse group of clinical disorders unified by elevated IgG4 levels and specific histopathologic findings. A key unanswered question is whether IgG4, a relatively weak activator of effector cells, is pathogenic in these disorders. Summary IgG4 is a unique antibody biologically and structurally. Increased understanding of its precise role in the clinical syndromes that comprise IgG4-RSD may ultimately elucidate the underlying pathogenesis. Erratum Due to an error at the publisher's office the name of one of the authors of this article was spelled incorrectly in the 2011 January issue of this journal . Frederick R. Taylor's surname was erroneously spelled as ‘Taylora’. However, the correct list of authors should read: “Ajay Nirula, Scott M. Glaser, Susan L. Kalled and Frederick R. Taylor”. The publisher apologizes for this error. Current Opinion in Rheumatology. 23(2):227, March 2011. © 2011 Lippincott Williams & Wilkins, Inc.