TLR9 and HIV infectious disease: Some researchers (15) have compared the ECs with other HIV infection groups and found that the pDCs of the ECs had a greater ability to reduce the production of HIV and induce T cell apoptosis in vitro, while the pDCs from patients with viral disease had almost no response without previous toll-like receptor 9 (TLR-9) stimulation, suggesting that pDCs in ECs may be involved in the control of HIV; however, the specific mechanism is still unclear.