Regulating immune cell functions: Dendritic cell-derived exosomes (DEX) carry MHC-II and co-stimulatory molecules, enhancing antigen presentation. Reducing autoimmune responses: Exosomes from tolerogenic dendritic cells suppress autoreactive T cells in diseases like rheumatoid arthritis and multiple sclerosis. Enhancing anti-inflammatory effects: Exosomes containing miR-150 and miR-21 inhibit NF-κB activation, reducing pro-inflammatory cytokine release. Acting as biomarkers: Circulating exosomal PD-L1 levels correlate with immune checkpoint activity in cancer and autoimmune diseases. This evidence concerns the gene NFKB1 and rheumatoid arthritis.