The anti-inflammatory effect of combined complement and CD14 inhibition is preserved during escalating bacterial load

Summary Combined inhibition of complement and CD14 is known to attenuate bacterial-induced inflammation, but the dependency of the bacterial load on this effect is unknown. Thus, we investigated whether the effect of such combined inhibition on Escherichia coli- and Staphylococcus aureus-induced inflammation was preserved during increasing bacterial concentrations. Human whole blood was preincubated with anti-CD14, eculizumab (C5-inhibitor) or compstatin (C3-inhibitor), or combinations thereof. Then heat-inactivated bacteria were added at final concentrations of 5 × 104−1 × 108/ml (E. coli) or 5 × 107−4 × 108/ml (S. aureus). Inflammatory markers were measured using enzyme-linked immunosorbent assay (ELISA), multiplex technology and flow cytometry. Combined inhibition of complement and CD14 significantly (P < 0.05) reduced E. coli-induced interleukin (IL)-6 by 40–92% at all bacterial concentrations. IL-1β, IL-8 and macrophage inflammatory protein (MIP)-1α were significantly (P < 0.05) inhibited by 53–100%, and the effect was lost only at the highest bacterial concentration. Tumour necrosis factor (TNF) and MIP-1β were significantly (P < 0.05) reduced by 80–97% at the lowest bacterial concentration. Monocyte and granulocyte CD11b were significantly (P < 0.05) reduced by 63–91% at all bacterial doses. Lactoferrin was significantly (P < 0.05) attenuated to the level of background activity at the lowest bacterial concentration. Similar effects were observed for S. aureus, but the attenuation was, in general, less pronounced. Compared to E. coli, much higher concentrations of S. aureus were required to induce the same cytokine responses. This study demonstrates generally preserved effects of combined complement and CD14 inhibition on Gram-negative and Gram-positive bacterial-induced inflammation during escalating bacterial load. The implications of these findings for future therapy of sepsis are discussed.