However, certain bacteria enriched in RA, such as Lachnospiraceae and S. didolesgii, exacerbate RA by overproducing primary indole and stimulating IL-6, IL-1β, and IL-17 signaling (124), underscoring a dual role of tryptophan metabolism that depends on the specific microbial and host context. Here, IL1B is linked to rheumatoid arthritis.