METHODS: Adult SSc patients, stratified according to 1) on immunosuppressive (On-IS) drugs or 2) no immunosuppressive drugs (No-IS), and age-and-sex-matched healthy controls (HC) were recruited. Metagenomic sequencing of stool DNA was compared between SSc patients and HC, and between SSc (On-IS) and (No-IS) patients. Alpha and beta-diversity, taxonomic and functional profiling were evaluated.

RESULTS: Twenty-three female SSc patients (12 On-IS; 11 No-IS; 5 diffuse and 18 limited SSc subtype) and 19 female HC, with median age of 54 years and 56 years, respectively, were recruited. Median SSc disease duration was 3.3 years. Alpha diversity was significantly higher in SSc versus HC (p=0.014) and in SSc (No-IS) versus HC (p=0.006). There was no significant difference in beta diversity between SSc and HC (p=0.307). At the phyla level, there were significantly increased abundance of Firmicutes and Actinobacteria in SSc versus HC, and reduced abundance of Bacteroidetes (all p<0.001). At the species level, there were significantly increased abundance of several Lactobacillus, Bifidobacterium, and Coprococcus species in SSc, and increased abundance of Odoribacter, Bacteroides and Prevotella species in HC. KEGG pathway analysis demonstrated distinct differences between SSc versus HC, and between SSc (No-IS) and SSc (On-IS).