Expression and function of Toll‐like receptor 9 in severely injured patients prone to sepsis

Summary The purpose of this prospective study was to enumerate Toll‐like receptor 9 (TLR9) + cells and measure their function using synthetic oligonucleotides enriched in CG dinucleotide motifs (CpG)‐induced proliferation within 48 h after trauma in severely injured patients prone to sepsis. Sixteen consecutive trauma patients with an injury severity score (ISS) > 21 and 16 blood donors (controls) were included in this study. Using two‐colour flow cytometry, TLR9 expression was detectable intracellularly and also on the surface of B lymphocytes. The surface expression of TLR9 of B lymphocytes from whole blood and peripheral blood mononuclear cells (PBMC) stimulated with CpG was significantly increased in B cells of severely injured patients prone to sepsis compared to controls. No significant differences could be observed between CpG‐induced proliferation of PBMC of severely injured patients prone to sepsis and controls. As a measure of immunosuppression, human leucocyte antigen (HLA)‐DR expression of monocytes of the trauma patients was significantly diminished compared with controls in PBMC and in whole blood. Immunosuppression in the early phase after trauma seems not to be associated with a disturbed sensing of bacterial DNA.