These antibodies were able to neutralize all the IL-10 producedin vitroby the APCs (Figure 3), and this blockage resulted in a similar increase in the production of pro-inflammatory cytokines after Bb co-culture as seen in the IL-10-/-APCs (compareFigures 2and3). little-to-no upregulation of several critical surface co-stimulatory markers by Ms and DCs, however eliminating Bb-elicited IL-10 OGN allowed a significant upregulation in CH5138303 many of these co-stimulatory receptors. These data indicate that IL-10 elicited from Bb-stimulated Ms and DCs results in decreased production of proinflammatory mediators and co-stimulatory molecules, and suppress phagocytosis-associated events that are important for mediating both innate and adaptive immune responses by APCs. == Introduction == Lyme disease is caused by the tick-borne spirochetal bacterium Borrelia burgdorferi (Bb)[1]. After deposition into the skin of susceptible hosts, this pathogen can rapidly migrate through skin tissues to infect and persist within many different tissues [2]. If diagnosed and treated with appropriate antibiotics in a timely manner, these bacteria are usually cleared from most patients without lasting symptoms. However, in the absence of antibiotic treatment, these pathogens can persist for months to years in a wide range of host tissues. Persistent bacteria can periodically re-emerge in those tissues to elicit inflammatory responses that cause the widely varying sequellae associated with Lyme disease; this is most commonly observed as inflammation in large joints, nervous and neurologic abnormalities, and cardiac-associated disorders. Notably, immunocompetent hosts are able to produce potent innate and adaptive immune responses against Bb during the course of infection. In vitrostudies have shown that macrophages and neutrophils can phagocytose and kill Bb quite efficiently, particularly if Bb-specific antibodies are present [3-5]. While the adaptive immune response to Bb is somewhat delayed, the antibodies produced during this response are able to bind Bb and mediate killingin vitroand passive transfer of these antisera into nave mice are able to prevent subsequent infection by similar Bb strains [6,7]. However, even though Bb appears to disseminate and persist largely within the extracellular tissues, where they should be readily accessible to both cellular and soluble immune mediators, these innate and adaptive immune effectors are unable to effectively clear these pathogens. Thus there is great interest in identifying the mechanisms that allow Bb to evade these immune responses. Appropriate innate immune responses appear to be particularly critical in controlling the development of Lyme disease [1,8]. The Bb genome encodes 127 different lipoproteins (e.g. ~8% of all open reading frames), many of which are believed to be important for their ability to rapidly adapt and persist within tick and vertebrate hosts [2,9-13]. CH5138303 While these numerous lipoproteins likely provide different biological functions, all appear to possess similar triacyl modifications at the amino terminal that promote their trafficking and insertion into the Bb outer membrane [14,15]. Murine studies have shown that innate receptors, most notably CD14 and toll-like receptor 2 (TLR2), can recognize the common triacyl motif on these lipoproteins and initiate inflammatory responses via MyD88-dependent pathways [16-20]. These TLR2-mediated signaling pathways are critical for macrophage (M) activation by Bb lipoproteins, leading to more efficient intracellular trafficking of Bb, and the production of a wide range of inflammatory mediators believed important for promoting Bb CH5138303 clearance [21,22]. It is likely that these pathways are also used in a number of other immune and non-immune cell types that are also directly activated by Bb lipoproteins, including dendritic cells (DCs) [23,24], neutrophils [25], mast cells [26], B cells [27], and endothelial cells [28,29]. Importantly, TLR2-deficient (TLR2-/-) mice infected with Bb possess up to 100-fold higher bacterial loads than wild-type mice in different tissues at both early and late times post-infection, even though these TLR2-/-mice CH5138303 produced Bb-specific antibodies at similar levels and of similar Bb-antigen specificity as infected wild-type mice [21,30]. These findings highlight the ability of these spirochetes to efficiently evade the adaptive immune responses and the importance of innate responses in controlling Bb levels during all stages of infection..