Date: Monday, November 9, 2015
Session Type: ACR Poster Session B
Session Time: 9:00AM-11:00AM
Background/Purpose: IgG antibodies expressing the idiotope for the 9G4 idiotype, the framework-1 hydrophobic patch (HP) of VH4-34, are expanded in SLE and provide a unique model to understand the participation of different autoantigens in the regulation of this disease. In particular the antibodies to single stranded RNA (ssRNA) have been implicated in viral infections in SLE. Here, we sought to understand the contribution of VH4-34 antibodies that bind to ssRNA in the pathogenesis of SLE.
A panel of 9G4 + monoclonal antibodies (mabs) was generated from IgD+ CD27- naïve B cells and IgD-CD27+ memory B cells of SLE patients. A total of 30 monoclonal antibodies, (20 native antibodies and corresponding HP altered mutants) were tested for anti-ssRNA binding by ELISA. Two representative antibodies with strong ssRNA reactivity were also tested against a proteome auantigen microarray and by immunofluorescence.
Out of the 30 mabs with diverse antigenic binding patterns, 2 derived from SLE memory B cells (22%) had strong autoreactivity with ssRNA. These antibodies also bound other Ags including: apoptotic and B cell binding, dsDNA, chromatin, Ribosomal P, and were also positive for ssRNA. These two antibodies were of the IgG3 subclass and were clonally related with a single amino acid difference within the CDR2, and identical CDR3 regions of the heavy chain. Further, the corresponding 9G4- HP mutant of these two abs showed binding to ssRNA albeit with decreased intensity.
Our preliminary results suggest that the anti-RNA response may be abundant in SLE memory B cells and mediated by expanded clones with a predominance of IgG3 antibodies. 9G4 mutagenesis experiments indicate that, while the HP may influence binding is not determinant of this type of autoreactivity. These findings are consistent with the lack of ssRNA binding of naïve antibodies and suggests that such autoreactivity is dependent on the conventional antigen binding site and may require somatic hypermutation. Larger studies will be required to understand the structural basis, generation and selection of ssRNA antibodies in SLE. Such studies will shed light into the role of exogenous and endogenous RNA antibodies to SLE autoreactivity.
This work was supported in part by the following grants from National Institute of Health (NIH): NIH-NIAID: 5R37AI049660-12; NIH-NIAID ACE U19: 1U19AI110483-02; NIH-NIAID P01: 5P01AI078907-05 and Georgia Research Alliance.
To cite this abstract in AMA style:Chida A, Cashman K, Jenks S, Hartson L, Wang Y, Li QZL, Mohan C, Sanz I. Binding of a Novel IgG3 VH4-34 Monoclonal Antibody to ssRNA in SLE [abstract]. Arthritis Rheumatol. 2015; 67 (suppl 10). https://acrabstracts.org/abstract/binding-of-a-novel-igg3-vh4-34-monoclonal-antibody-to-ssrna-in-sle/. Accessed December 11, 2019.
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