Anti-neutrophil cytoplasm antibody IgG subclasses in Wegener's granulomatosis: a possible pathogenic role for the IgG4 subclass

Abstract

SUMMARYA characteristic feature of Wegener's granulomatosis is the presence of antineutrophil cytoplasm antibodies (ANCA) to proteinase 3 (PR3). In vitro , ANCA activate neutrophils by co-ligating PR3 and Fc g RIIa/IIIb receptors. ANCA are predominantly of the IgG isotype, and IgG1, IgG3 and IgG4 subclasses are particularly represented. To address the pathogenic role of individual ANCA-IgG subclass antibodies, patients' sera were screened using indirect immunofluorescence, enzyme-linked immunosorbent assay (ELISA) and subclass PR3-ELISA to identify patients with high titres of PR3-ANCA within the IgG1, IgG3 or IgG4 subclasses. Unfractionated ANCA-IgG and subclass fractions were isolated by affinity chromatography and compared for their capacities to stimulate superoxide production by primed human neutrophils. Donor neutrophils were analysed for constitutive and induced Fc g RI expression by flow cytometry. The IgG1, IgG3 and IgG4 subclass fractions, isolated from three different ANCA sera, each stimulated superoxide production from neutrophils derived from multiple donors. Subsequently, IgG4 subclass fractions isolated from a further four ANCA positive sera demonstrated varying abilities to stimulate release of superoxide; unrelated to PR3-ANCA titre, neutrophil donor, or neutrophil Fc g RI expression. The stimulation of superoxide release by IgG1-and IgG3-ANCA subclass fractions is consistent with the proposed mechanism of co-ligation of PR3 antigen and Fc g RIIa/IIIb receptors. However, the demonstration of similar activity for the IgG4-ANCA subclass fractions isolated from some sera was unexpected. This activity was independent of neutrophil donor and expression of Fc g RI, suggesting it was capable of activating neutrophils via constitutively expressed Fc g RIIa/IIIb or co-ligation of other, unidentified, cell surface molecules.

An abundance of IgG4+ plasma cells is not specific for IgG4-related tubulointerstitial nephritis

“…This finding is noteworthy in view of recent interest in the possible role of IgG4 ANCA in the pathogenesis of small-vessel vasculitis, [13][14][15] but our IgG4 þ PC-rich cases were not clearly different, based on ANCA status or immunopathological findings, from the 11 NCGN cases in the survey with few or no IgG4 þ PC. Despite the frequent finding of autoantibodies in patients with IgG4-SD, we are not aware of reports of ANCA in this setting.…”

IgG2m4, an engineered antibody isotype with reduced Fc function

“…Briefly, the heavy or light chain expression cassette comprises a human CMV (HCMV) promoter and leader sequence on the 5' end of a cloning site, and the sequences for constant regions (kappa or lambda light chain and IgG2m4 for heavy chain, respectively) and bovine growth hormone (BGH) polyadenylation signal on the 3' side shorter half-life when compared to that of IgG1 and IgG2, 37 and possible IgG4 connection with Wegener granulomatosis. 38 It is not clear how much IgG4 function still remains in IgG2/4 due to its intact IgG4 CH2 and CH3.…”

Proteinase 3 Anti-Neutrophil Cytoplasmic Antibody (PR3-ANCA) Positive IgG4-Related Retroperitoneal Fibrosis: Utility of PET-CT with ¹⁸F-Fluorodeoxy Glucose (FDG)

“…Although the previous authors did not comment on the serum levels of IgG4, these reports are generally thought to be cases of IgG4-related disease, even though this is the first reported case with a combination of IgG4-related retroperitoneal fibrosis and elevated PR3-ANCA (Table 1). Regarding the relationship between IgG4 and PR3-ANCA, recent several analyses demonstrate the importance of IgG4 subclass of PR3-ANCA, which induces inflammation in patients with Wegener's granulomatosis (5,34,35). Further accumulation of similar cases will help clarify the mechanisms of retroperitoneal fibrosis and the relationship between PR3-ANCA and IgG4.…”

“…Recently, retroperitoneal fibrosis is reported to belong to IgG4-related diseases, which is proposed as a new disease entity by many Japanese physicians, based on the criteria of IgG4 greater than 135 mg/dL (3,4). On the other hand, proteinase 3 anti-neutrophil cytoplasmic antibody (PR 3-ANCA) is a well known disease marker autoantibody found in Wegener's granulomatosis (5). However, several other diseases are reported to be associated with PR3-ANCA (6)(7)(8).…”