Mucous membranes and their microbiomes play a role in the genesis of rheumatoid arthritis (RA). However, this assertion is mainly based on animal experiments. The aim of this thesis was to analyze human samples.

We collected 380 stool and serum samples from the SCREEN-RA cohort (individuals at risk of RA). Participants were then classified as controls, high genetic-risk controls, asymptomatic individuals but with RA-specific auto-antibodies, and individuals with clinically suspect arthralgia or new-onset RA.

We were unable to identify any notable intestinal inflammation in early RA patients, nor in individuals at high risk of RA. In our data, the presence of intestinal bacteria known to worsen arthritis in mice was not associated with autoimmunity or the onset of RA.

The technical limitations and future research directions are also extensively discussed.