Autoantibodies associated with RNA are more enriched than anti-dsDNA antibodies in circulating immune complexes in SLE

Abstract

To what extent different autoantibodies accumulate in systemic lupus erythematosus (SLE) immune complexes (ICs), and whether such accumulation is associated with disease activity has been investigated. ICs were isolated from SLE sera by both polyethylene glycol (PEG) precipitation and C1q-binding. Autoantibody specificities were determined using a lineblot assay quantified by densitometry. To compare the relative levels of autoantibodies, levels were normalized to the total levels of IgG measured by ELISA in sera and parallel ICs. Samples were investigated both in a cross-sectional design as well as in a paired design with samples obtained during both active and inactive SLE. All investigated autoantibody specificities except anti-dsDNA were enriched in circulating ICs as compared with parallel sera. The group of antibodies against RNA-associated antigens (anti-RNP/Sm, anti-Sm, anti-SSA/Ro60, anti-SSA/Ro52, anti-SSB/La) all exhibited higher median enrichment than the DNA-associated (anti-dsDNA, anti-histones, anti-nucleosomes) or cytoplasmic (anti-ribosomal P) antigens. In particular autoantibodies against RNP/Sm and SSA/Ro52 had the highest degree of enrichment in SLE PEG precipitates. These findings were corroborated by analysis of autoantibody content in C1q-bound ICs. There was no difference in degree of IC accumulation of the investigated autoantibodies during active and inactive SLE. Our findings demonstrate a difference in enrichment between autoantibodies against RNA- and DNA-associated autoantigens in isolated SLE IC, suggesting that the RNA-associated autoantibodies are more prone to form circulating ICs in SLE, in contrast to antibodies against DNA-associated autoantigens such as dsDNA. These finding have implications in understanding mechanisms of differential autoantibody accumulation in target organs in SLE.

Toll‐Like Receptor 9 Deficiency Breaks Tolerance to RNA‐Associated Antigens and Up‐Regulates Toll‐Like Receptor 7 Protein in Sle1 Mice

“…This is supported by clinical data that shows a preferentially higher TLR-7 expression in SLE patients with an anti-RNA-associated antibody profile (47). Additionally, it has recently been shown that RNAassociated antibodies are more prone to form circulating ICs compared to antibodies to dsDNA (48). U1 RNA, which forms the U1 snRNP complex together with Sm and RNP proteins (49), is elevated in the circulation of SLE patients and correlates with disease activity (50).…”

Estrogen modulation of endosome-associated toll-like receptor 8: An IFNα-independent mechanism of sex-bias in systemic lupus erythematosus

“…Since endosomal TLRs have a much more controlled mechanism of antigen exposure and are not free to sample the environment in an unregulated manner, this may explain why positive agonist-induced regulation of receptor expression may only exist in TLRs localized to endosomes. Endosome-associated TLRs exclusively bind to nucleic acids and SLE patients often secrete high levels of anti-nuclear antibodies (ANA), which results in circulating immune complexes consisting of antibodies to self nucleic acids [53]. Our data suggest that processing of these complexes could cause a ligand-induced up-regulation of receptor expression, which would be more robust in an environment containing estrogen and therefore contribute to autoimmune development.…”

Discovery of biomarkers for systemic lupus erythematosus using a library of synthetic autoantigen surrogates

“…Soluble immune complexes in lupus sera have been analyzed by precipitation in polyethylene glycol (PEG) or by their binding to C1q (Skinner and Maddison, 1990; Ahlin et al, 2012). The two methods are not completely identical, as lupus patients also produce autoantibodies to the collagen like domain of C1q that bind independent of immune complexes (Uwatoko and Mannik, 1988; Mannik and Wener, 1997).…”

“…The two methods are not completely identical, as lupus patients also produce autoantibodies to the collagen like domain of C1q that bind independent of immune complexes (Uwatoko and Mannik, 1988; Mannik and Wener, 1997). Detailed analysis of PEG precipitated immune complexes from lupus patients suggests that the circulating complexes are enriched in antibodies binding RNA but not anti-double stranded DNA (Ahlin et al, 2012). This is consistent with the frequent finding of antibodies to Ro52 and RNP in the SLE15 purified IgG from both lupus and control sera.…”