A COMPARATIVE-ANALYSIS OF CYTOKINE PRODUCTION AND TOLERANCE INDUCTIONBY BACTERIAL LIPOPEPTIDES, LIPOPOLYSACCHARIDES AND STAPHYLOCOCCUS-AUREUS IN HUMAN MONOCYTES

Monocytes (MO) and macrophages (MAC) are important producers of cytoki nes involved in the pathophysiology of bacterial sepsis. Most studies concentrate on the effects of bacterial lipopolysaccharides (LPS) rega rding the induction of cytokine gene expression and secretion in MO/MA C. Here we report that besides LPS, the synthetic lipoprotein analogue lipopeptide mitoyl)-(2RS)-propyl)-(R)-cysteinyl-alanyl-glycine (Pam3- Cys-Ala-Gly), another component of the outer membrane of Gram-negative bacteria, as well as heat-killed Staphyloccocus aureus (S. aureus/SAC ) are potent stimuli for cytokines in human MO. For all three investig ated stimuli we found an individual pattern of cytokine induction: LPS was most potent in inducing interleukin-6 (IL-6) synthesis, whereas f or tumour necrosis factor-alpha (TNF-alpha) secretion SAC was the best stimulus. Comparable amounts of IL-8 were induced by either LPS or Pa m3-Cys-Ala-Gly, with SAC being less effective even at higher concentra tions. The addition of serum led to an increase in LPS-, SAC- and Pam3 -Cys-Ala-Gly-stimulated TNF-alpha secretion, indicating that the prese nce of serum is critical not just for LPS stimulation. Furthermore, as is known for LPS, Pam3-Cys-Ala-Gly and SAC rendered MO refractory to a second bacterial stimulus. Pam3-Cys-Ala-Gly and SAC induced toleranc e for itself, but LPS could partially overcome this effect. As the CD1 4 molecule is discussed as a common receptor for different bacterial c omponents, we investigated whether the TNF-alpha response of MO could be blocked by anti-CD14 antibodies. MY4, a CD14 antibody, selectively blocked the TNF-alpha secretion induced by LPS but not by Pam3-Cys-Ala -Gly or SAG. In summary, we conclude that besides LPS, lipopeptide Pam 3-Cys-Ala-Gly and SAC are potent stimuli for human MO, while the mecha nisms of activation seem to be partially different from LPS.