Background/Purpose: Autoantibody production precedes SLE or SS by years, including anti-Ro. Anti-Ro⁺ mothers of children with congenital heart block (CHB) are a unique population at risk for pathologic autoimmunity, as many are asymptomatic (Asym/UAS) and become aware of autoantibodies due to fetal disease and yet have a 10-year progression rate to SS/SLE of 20%-30%. We hypothesized that variation in the oral microbiome correlates with transition to SLE or SS and pathogenicity involves sequence homology between Ro60 and bacterial von Willebrand factor type A domain protein (vWFA).

Methods: The oral microbiome of 25 anti-Ro⁺ mothers of CHB children (Asym/UAS, N=9; SS/SLE, N=16) and 7 healthy controls (HC) were processed using 16S ribosomal RNA sequencing. Analysis of variance methods compared the centered log ratio transformed relative abundances for 1) HC vs. anti-Ro⁺ mothers, and 2) assuming an ordering of severity from HC < Asym/UAS < SS/SLE. To adjust for multiple comparisons, a taxonomic stepdown method coupled with false discovery rate (FDR) was used. The Basic Local Alignment Search Tool evaluated homology of Ro60 at aa 371-381 and peptides of vWFA.

Results: Sequencing 16S rRNA identified microorganisms from 2 kingdoms, 16 phyla, 25 classes, 41 orders, 70 families, 164 genera, and 166 species. The Shannon Index (H) revealed that for each taxonomic level except species, there were significant reductions in diversity in the anti-Ro⁺ mothers relative to HC (P ≤ 0.05). There were global differences in the microbiota of these mothers relative to HC (perMANOVA P=0.00049). The phylum Actinobacteria was more abundant in the anti-Ro⁺ mothers vs HC (P_FDR=0.0231).  Within Actinobacteria, the class Coriobacteriia and subsequent lower taxonomic levels down to Atopobium parvulum, all exhibited increases in relative abundance in the anti-Ro⁺ mothers compared to HC. There was a significant reduction in the relative abundance as clinical severity increased within one of the most frequent phyla, Proteobacteria (P_FDR=0.030; mean±SD; HC 0.24±0.07; Asym/UAS 0.19±0.12; SS/SLE 0.11±0.08). The difference in the relative abundances between Asym/UAS and SS/SLE within Proteobacteria was significant (P=0.042). Within Proteobacteria, the common class Betaproteobacteria also showed reduced relative abundance with increasing clinical severity (P_FDR=0.0037; HC 0.11±0.04; Asym/UAS 0.072±0.07; SS/SLE 0.031±0.04). These ordered differences were maintained down the taxonomic hierarchy to the genus (Lautropia, P_FDR=0.0072) and species within this genus (L. mirabilis, P_FDR=0.012). Next, sequences of vWFA secreted by these taxa were evaluated.  For a comparison of Ro60 T cell epitope, FLLAVDVSASMNQ, the vWFA, VLVVFDNSSSMTA vWFA of A. parvulum was not a fit due to the aromatic and polar aa at positions 5 and 9, respectively. In contrast, the vWFA of L. mirabilis, LLLLLDVSGSMAG, was identical at 7 of the first 11 aa.

Conclusion: These data provide evidence that the microbiome differs along a clinical spectrum of autoimmunity.  In part, the data reflect a path involving depletion of L. mirabilis, which is secondary to a pathologic role of anti-Ro along with an expansion of A. parvulum, an opportunistic taxon.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-oral-microbiome-as-a-risk-factor-for-benign-or-pathologic-autoimmunity-associated-with-anti-ssa-ro-positivity-and-mimicry-for-von-willebrand-factor-type-a-domain-protein-vwfa-of-l-mirabilis/