Sir, We note with interest the response from Mattman et al. . We agree that serum IgG subclass measurement is known to be associated with potential analytical errors as described. The methodology for serial IgG subclass measurement in this case was the binding site assays for the Siemens BNII™ nephelometer (latex enhanced for IgG3 and IgG4). The settings were changed between 2014 and 2015 to correct for antigen excess errors. We also agree that patients historically assessed as unlikely to have the disease, based solely on a low or normal serum IgG4 concentration, should be reassessed. Our previous work, however , has demonstrated, using double staining immunohistochemistry, that in patients with IgG4-related orbital disease there is a real elevation of tissue IgG2 plasma cells, distinct from tissue IgG4. It is still our belief, therefore, that the role of both serum and tissue IgG2 in the context of IgG4-RD may not be solely the result of analytical error and assay cross-reactivity. It is a phenomenon that requires further exploration and explanation. Funding: No specific funding was received from any bodies in the public, commercial or not-for-profit sectors to carry out the work described in this manuscript. Disclosure statement: The authors have declared no conflicts of interest. References 1 Mattman A , Chen LYC , van der Gugten G et al. Comment on: IgG4-related disease presenting with raised serum IgG2—real timeline of IgG4-RD? Rheumatology 2018 ; 57 : 1125 – 6 . 2 Chan ASY , Mudhar H , Shen SY et al. Serum IgG2 and tissue IgG2 plasma cell elevation in orbital IgG4-related disease: potential use in IgG4-RD assessment . Br J Ophthal 2017 ; 101 : 1576 – 82 . Google Scholar CrossRef Search ADS © The Author(s) 2018. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved. For Permissions, please email: firstname.lastname@example.org This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)
Rheumatology – Oxford University Press
Published: Mar 23, 2018
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