Altered Bacterial Profiles at Genus Level in the Gut of Ankylosing Spondylitis Patients with Different ASDAS Scores

Ankylosing spondylitis (AS) is a chronic inflammatory autoimmune disease that is characterized by sacroiliitis and spondylitis, which may lead to extreme bony ankylosis.1,2 The current prevalence in the Chinese Han population ranges from 0.20% to 0.54%.3 As many as 60% of patients with spondyloarthritis (SpA) have subclinical intestinal inflammation,4 wherein up to 10% of these have more significant clinically apparent Crohn's disease. Microbial disorders and changes in innate immune response have been confirmed in the gut of AS patients.5 Therefore, it is logical to consider that gut microbiota may play an important role in the pathogenesis of AS. AS Disease Activity Score (ASDAS) is a new comprehensive index to evaluate the degree of AS disease activity.6 The 3 cutoff values chosen to distinguish these states are: <2.1 low disease activity, between 2.1 and 3.5 high disease activity, and >3.5 very high disease activity.7,8 We investigated the bacterial profiles of fecal specimens of AS cases with different ASDAS scores by using 16S ribosomal RNA gene sequencing technology. All participants who had used any antiinflammatory drugs in the 4 months prior to sampling were excluded from our study. Microbial DNA was extracted, amplified and followed by highthroughout sequencing. The population of AS cases with a male predominance,9 our study consisted of 82.83% males, and the average age was 33.72 years. AS cases with low score of ASDAS (<2.1, n = 9, LSAS), medium score of ASDAS (2.1 to 3.5, n = 21, MSAS), and high score of ASDAS (>3.5, n = 10, HSAS) and health controls (n = 20, HC) were investigated, respectively (Table 1, Figure 1A). We analyzed the profiles of diversityin gut microbiota by bioinformatics analysis to reveal the signatures at the genus level of AS cases with different ASDAS scores. A representative result was shown in Fig S1. Discriminant analysis was conducted using linear discriminant analysis coupled with effect size (LEfSe) to identify significant altered bacterial profiles at the genus level (Figure 1B,C). When compared with group HC, 19 genera, 14 genera and 13 genera was altered notably in groups HSAS, MSAS and LSAS, respectively. 9 genera with different abundance were found between group LSAS and group MSAS. In additional, compared with the HSAS group, 5 and 3 altered genera were found in the LSAS group and MSAS group, respectively. Importantly, a strong hint was found between the presence of pathogenic microbiota and ASDAS. The relative abundances of opportunistic pathogens Ruminococcus_2, Ruminococcaceae_ UCG_014, especially, Clostridium_sensu_stricto_1 increased notably in the high score ASDAS group. Although hydrogenproducing genus Clostridium_sensu_stricto_1 has been reported to be significantly