TLR9 and rheumatoid arthritis: TLR9 is an endosomal pattern recognition receptor (PRR) known to recognize CpG (cytosine-phosphodiester bond-guanine)-rich unmethylated DNA such as that of the nascent EBV genome (5).We further showed that EBV DNA has immune stimulatory capabilities in mice via enhancing the production of the pro-inflammatory interleukin 17A (IL-17A), a cytokine associated with autoimmune diseases such as rheumatoid arthritis (RA), multiple sclerosis (MS) and systemic lupus erythematosus (SLE).