TLR9 and bacterial infectious disease: This finding provides insight into the potential explanation for the observed lower expression of TLR9 on the surface of red blood cells in patients with bacterial infection compared to healthy individuals: perhaps due to the increased binding of mtDNA to the surface of red blood cells in infected patients, which may obscure the detection sites of TLR9, resulting in reduced TLR9 expression on the surface of red blood cells in patients with bacterial infection.