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Background: The innate immune system is suppressed after major orthopaedic surgery, implicating a risk of septic complications. Whole-blood ex vivo testing with lipopolysaccharide (LPS) has shown a depression of the tumour necrosis factor alpha (TNF-α) production until 12 days postoperatively. As part of the innate immune system, the Toll-like receptors TLR2 and TLR4 recognize antigens from Gram-positive and Gram-negative bacteria, respectively. The receptors CD14 and CD11b are involved in the LPS receptor complex, whereas human lymphocyte antigen (HLA)-DR binds endotoxin peptides. It is still uncertain whether the expression of all these receptors changes after major surgery. Methods: In 6 patients undergoing hip arthroplasty, we investigated three times the display of TLR4, TLR2, CD14, CD11b, and HLA-DR on monocytes by fluorescence-activated cell sorting and white blood cell counts during 12 days postoperatively. At the same time, the plasma levels of interleukin (IL)-1β, IL-4, IL-6, IL-10, IL-13, and TNF-α were measured. Results: There was no significant change in the expression of TLR4, CD14, CD11b, HLA-DR, and TLR2. Monocyte count and cytokine analysis did not differ from the ones pre-operatively taken. Conclusions: After aseptic orthopaedic surgery, there is no change in the display of the LPS receptor complex on monocytes. Other mechanisms have to be investigated to gain insight into the decrease of the TNF-α production capacity postoperatively. Copyright © 2008 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]