CD4 and rheumatoid arthritis: Synovial inflammation and hyperplasia with pannus formation, as well as bone and cartilage destruction, are the fundamental pathological features of RA.1,4 Fibroblast-like synoviocytes (FLSs) are a key component of the synovial pannus, displaying a uniquely aggressive phenotype and actively contributing to the pathological progression of RA.41 In the RA synovium, FLSs can function as antigen-presenting cells, internalize NET products, upregulate MHC class II molecules, and present NET-derived peptides to CD4 + T cells,42 establishing an association with the adaptive immune response in RA.