IL6 and rheumatoid arthritis: In a randomized, double-blind and placebo-controlled clinical trial, the levels of pro-inflammatory cytokines (such as TNF-α and IL-6) were significantly reduced in patients with Lactobacillus casei supplementation, and the clinical symptoms (such as joint swelling and pain) of patients also improved compared with those in the control group, indicating that probiotics may improve the symptoms of RA by adjusting the composition of the intestinal flora, enhancing the immune function, and reducing systemic inflammatory response [69,133].