A comparative analysis of cytokine production and tolerance induction by bacterial lipopeptides, lipopolysaccharides and <em>Staphyloccocus aureus</em> in human monocytes.

Monocytes (MO) and macrophages (MAC) are important producers of cytokines involved in the pathophysiology of bacterial sepsis. Most studies concentrate on the effects of bacterial lipopoly-saccharides (LPS) regarding the induction of cytokine gene expression and secretion in MO/MAC. Here we report that besides LPS, the synthetic lipoprotein analogue lipopeptide N-palmitoyl-S-( 2,3-bis (palmitoyl)-(2RS)-propyl)-(R)cysteinyl-alanyl-glycine (Pam 3-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 investigated stimuli we found an individual pattern of cytokine induction: LPS was most potent in inducing interleukin-6 (IL-6) synthesis, whereas for tumour necrosis factor-α (TNF-α) secretion SAC was the best stimulus. Comparable amounts of IL-8 were induced by either LPS or Pam3-Cys-AlaGly, with SAC being less effective even at higher concentrations. The addition of serum led to an increase in LPS-, SAC- and Pam3-Cys-Ala-Gly-stimulated TNT-α secretion, indicating that the presence 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 tolerance for itself, but LPS could partially overcome this effect. As the CD14 molecule is discussed as a common receptor for different bacterial components, we investigated whether the TNF-α response of MO could be blocked by anti-CD 14 antibodies. MY4, a CD14 antibody, selectively blocked the TNF-α secretion induced by LPS but not by Pam3-Cys-AIa-Gly or SAC. In summary, we conclude that besides LPS, lipopeptide Pam3-Cys- Ala-Gly and SAC are potent stimuli for human MO, while the mechanisms of activation seem to be partially different from LPS. [ABSTRACT FROM AUTHOR]