title: Immune Complex-Mediated Complement Activation in a Patient with IgG4-Related Tubulointerstitial Nephritis.
abstract: A 59-year-old man was diagnosed with IgG4-related tubulointerstitial nephritis. His symptoms as well as laboratory and imaging findings were improved after initiation of steroid therapy. Serologically, he showed hypocomplementemia (C3 23 mg/dl, C4 <2 mg/dl, CH50 <7 U/ml) with high levels of IgG (IgG4 1,970 mg/dl) and immune complexes (C1q assay 8.1 μg/ml) and a low level of C1q (<2.0 mg/dl). Histologically, he also showed linear depositions of IgG, IgM, C3, C4d, C1q, membrane attack complex and all IgG subclasses (IgG1, IgG2, IgG3 and IgG4) along the tubular basement membrane, as well as granular depositions of these components in the renal interstitium. However, mannose-binding lectin and L-ficolin were not detected in these tissues. Homogeneous electron-dense deposits were observed by electron microscopy in the tubular basement membrane. It appears that the immune complexes might activate the classical pathway of the complement in both blood and local tissues in a patient with IgG4-related tubulointerstitial nephritis.
authors.affiliation: Division of Nephrology, Department of Internal Medicine, Juntendo University Faculty of Medicine, Tokyo, Kanagawa, Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Nagamachi
authors.forename: Isao
authors.initials: I
authors.lastname: Ohsawa
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Sato
authors.forename: Masaya
authors.initials: M
authors.lastname: Ishii
authors.forename: Gaku
authors.initials: G
authors.lastname: Kusaba
authors.forename: Takashi
authors.initials: T
authors.lastname: Kobayashi
authors.forename: Yukihiko
authors.initials: Y
authors.lastname: Takeda
authors.forename: Satoshi
authors.initials: S
authors.lastname: Horikoshi
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ohi
authors.forename: Misao
authors.initials: M
authors.lastname: Matsushita
authors.forename: Yasuhiko
authors.initials: Y
authors.lastname: Tomino