Induction of pro- and anti-inflammatory cytokines by Borrelia burgdorferi lipoproteins in monocytes is mediated by CD14

We previously showed that heat-killed Borrelia burgdorferi spirochetes and lipidated outer surface protein A (L-OspA) stimulated the in vitro producti on of interleukin-10 (IL-10) in peripheral blood mononuclear cells (PBMC) f rom uninfected humans and rhesus monkeys (G. Giambartolomei et al,, Infect. Immun, 66:2691-2697. 1998), Here we demonstrate that uninfected human peri pheral blood monocytes, but not B or T cells, are the cells that transcribe the IL-10 cytokine gene in response to heat-killed B, burgdorferi. B, burg dorferi similarly induced an upregulation of the IL-1 beta and IL-6 cytokin e genes in monocytes and the production of IL-10 and IL-6 in culture supern atants of the human monocytic cell line THP-1, Purified L-OspA (but not unl ipidated OspA [U-OspA] or U-OspC) also stimulated the production of both cy tokines in THP-1 cells in a dose-dependent fashion, suggesting that acylati on of the OspA protein molecule is required for the production of both anti - and pro-inflammatory cytokines in naive monocytes. A lipohexapeptide that contained the tripalmitoyl-modified cysteine motif (Pam(3)Cys-Hex) of B. b urgdorferi lipoproteins but with an arbitrary peptide sequence had the same effect. Monoclonal antibodies (MAbs) MY4 and 60bca, both of which bind to CD14 and are known to block lipopolysaccharide (LPS)-mediated cytokine prod uction, were able to block L-OspA-mediated LL-IO and IL-6 cytokine producti on. In contrast, MAb 26ic, which also binds to CD14 but does not block LPS function, failed to inhibit L-OspA-mediated cytokine production These data suggest that activation of monocytes and production of both anti- and pro-i nflammatory cytokines induced by lipoproteins proceeds via the CD14 recepto r. LPS binding protein was not required for OspA-induced cytokine productio n. Our results demonstrate that pro- and anti-inflammatory cytokines induce d by B. burgdorferi lipoproteins in PBMC are produced by monocytes and that lipoprotein and LPS signaling pathways share at least the initial signalin g event that involves the CD14 receptor.