Background/Purpose: SLE is characterized by the dysregulation of humoral immunity including high levels of autoreactive IgG VH4.34 antibodies recognized by the rat anti-human idiotypic antibody 9G4 (9G4+). VH4.34 antibodies have a germ line encoded anti-self specificity for blood antigen glycolipids and glycolipid epitopes of the B220 isoform of CD45 expressed on naïve B cells. As a consequence, naïve B cells from SLE patients can have high levels of 9G4 staining ex vivodue to surface bound VH4.34 antibodies. Serum 9G4+ IgG is correlated with high disease activity, lupus nephritis and anti-dsDNA. The role of B cell binding (BCB) 9G4+ in lupus pathogenesis and its potential clinical correlates is unclear.

Methods: 161 SLE (4 or more ACR criteria) patients were analyzed, including 24 patients with active nephritis. SLE patients were compared to 30 healthy controls or 15 RA, 15 Dermatomyositis, 26 scleroderma, and 7 pSS patients analyzed as autoimmune controls. 9G4+ BCB was measured ex vivo by flow cytometry and BCB was quantified as the ratio of the median fluorescence intensity of naïve B cells to that of switched memory. The resulting B cell binding ratio (BR) ranged from 1 (no binding) to 20 (very high binding) patients with a BR higher than 2.5 were considered positive. 9G4+ IgG, IgM, and IgA were measured by ELISA, capturing with the rat monoclonal 9G4 and detecting with goat anti-human IgG, IgM, or IgA.

Results:

BCB binding was highly specific for SLE as 33% of SLE patients were BCB positive compared to only 1.6% of autoimmune control patients and none of the HCD. Lupus patients with high disease activity or active nephritis were significantly more likely to have BCB than patients with low disease activity (47% and 54% as compared to 24% for low disease activity). When we compared BR to serum 9G4+ IgG concentration we found only a weak correlation (p=0.04, r=0.26). However, SLE patients had elevated 9G4+ IgM and IgA and the concentration of these isotypes was more strongly correlated with BCB (IgM p >0.001, r= 0.586) (IgA p>0.001, r=0.4602 ). IgA BCB was demonstrated directly by the detection of both surface 9G4 and IgA staining of healthy control donor naïve B cells after incubation with serum from an SLE patient. Patients with high BR had higher disease activity (p=0.021) and were more likely to have a history lupus nephritis (p=0.002) but this was not true for serum 9G4+ isotypes measure in either isolation or combination.

Conclusion:

The degree of B cell bound 9G4+ in some SLE patients is striking. Here we show that this auto-reactivity is specific to lupus and is more common in patients with active disease and active lupus nephritis. Interestingly, this association between B cell bound 9G4+ and disease activity is stronger than the association between serum 9G4+ IgG. As suggested by our data, this may be consequence of BCB measuring 9G4+ antibodies of multiple isotypes. The combination of IgA and IgG anti-dsDNA is more predictive of disease activity than either isotype alone and the same may be true for BCB 9G4+. In this light our finding that 9G4+ IgA is elevated in SLE patients and can bind B cells is intriguing. BCB 9G4+ may be a useful assay for stratifying SLE patients into clinically and immunologically distinct groups in future clinical and mechanistic studies.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/b-cell-binding-autoreactive-vh4-34-antibodies-are-specific-to-lupus-consist-of-diverse-isotypes-and-are-associated-with-high-disease-activity-and-lupus-nephritis/