Spondyloarthritis (SpA) and Rheumatoid arthritis (RA) are among the most common chronic inflammatory rheumatic diseases. Introduction of Tumor Necrosis Factor alpha inhibitors (TNFi) to the therapeutic strategy improved acute inflammation and pain, but a significant percentage of patients develop severe adverse events or are still non responders or incomplete responders to these expensive treatments. There is an urgent need to identify new predictors of biological therapy response. It has been described the role of microbiota in some rheumatic diseases, however, clinical trials are scarce. We hypothesized that microbiota or their metabolites may play a role in therapeutic response to TNFi.

Thus, this project aimed to evaluate the influence of oral and gut microbiota in the therapeutic response to biologic therapies, in 60 patients.

It is expected to enrolled 30 SpA and 30 RA patients and 30 controls, crossed by gender, age and diet profile. Oral and fecal microbiota will be characterized before TNFi therapeutic. Patients will have an additional microbiota and metabolic profile characterization 14 weeks late after.

This will allow to identify specific profiles of oral and gut microbiome and/or specific biochemical patterns in these patients. At week 14 it will be possible to identify changes induced by TNFi. In addition, it will be possible to identify microbiota pattern associated clinical therapeutic TNFi response vs non-response.

This will allow to predict isolate microbe or microbes patterns at baseline associated to clinical response obtained at week 14. These results may additionally contribute to clinical decision and a better evidenced-based treatment.

Inclusion Criteria:

1. Diagnosis of axSpA (according to ASAS classification criteria) or RA (according to 2010 ACR/EULAR classification criteria);
2. Indication for bDMARD therapy, according to the Portuguese recommendations for the use of biological therapies in patients with axSpA and RA;
3. Oral corticosteroids (equivalent to prednisolone ≤ 10mg/day) and/or nonsteroidal anti-inflammatory drugs allowed at stable dose ≥4 weeks before baseline;
4. Conventional DMARDs allowed at stable dose ≥12 weeks before baseline;
5. Ability to provide informed consent.

Exclusion Criteria:

1. History of rheumatic disorder other than axSpA or RA;
2. History of Inflammatory Bowel Disease;
3. Previous treatment with bDMARD;
4. Current pregnancy or breastfeeding;
5. Malignancy (except for completely treated squamous or basal cell carcinoma);
6. Any uncontrolled medical condition (e.g., uncontrolled diabetes mellitus, unstable ischemic heart disease);
7. History of any documented gastrointestinal disease or tract surgery leaving permanent residua (e.g., gastrectomy, bariatric surgery, or colectomy);
8. Intraarticular injections of extra-axial joints and tendons within 28 days before or at baseline;
9. Recent (<3 months prior) use of any antibiotic therapy, current extreme diet (e.g., parenteral nutrition or macrobiotic diet), current consumption of probiotics.

Control group will be healthy participants, and the same inclusion and exclusion criteria will be applied except for rheumatic disease diagnosis.

Patients with axSpA or RA according to ASAS and 2010 ACR/EULAR classification criteria, respectively, with indication to start bDMARD according to Portuguese Rheumatology Society.