CD64 is a high-affinity Fc(gamma)RI receptor expressed by activated neutrophils that has been recently evaluated as a potential sepsis parameter. In the present study, the kinetics of neutrophil membrane CD64 expression were examined during a standardized inflammatory response, using a human endotoxemia model, and compared with hematological indices, CRP, cytokines and interleukins. Ten healthy subjects received 2 ng/kg intravenous Escherichia coli lipopolysaccharide (LPS). After administration of LPS, neutrophil CD64 showed a biphasic response, characterized by a first increase from 108.5 +/- 7.5 to 133 +/- 6 AFU after 1 h (P = 0.047) and a second increase that started at 6 h and reached its maximum of 167 +/- 13 AFU at 22 h (P < 0.0001). CRP concentrations increased to 40 +/- 5 mg/dl 22 h after the administration of LPS. The cytokines and interleukins reached their maximum response within 1-2 h. The maximum values of pro-inflammatory cytokines (TNF-alpha, IFN-gamma and IL-6) correlated with the CD64 expression at 22 h after LPS administration (r(2) = 0.76, r(2) = 0.78, r(2) = 0.81, respectively, all P < 0.05), whereas this correlation was not found for the anti-inflammatory IL-10 (r(2) = 0.058, P = 0.54), suggesting that neutrophil CD64 expression might be a quantitative marker for innate immunity that could easily be used in the clinical setting.