Search

Lyme disease is a chronic inflammatory disorder caused by the spirochetal bacterium, Borrelia burgdorferi. In vitro evidence suggests that binding of spirochetal lipoproteins to CD14, a pattern recognition receptor expressed on monocytes/macrophages and polymorphonuclear cells, is a critical requirement for cellular activation and the subsequent release of proinflammatory cytokines that most likely contribute to symptomatology and clinical manifestations. To test the validity of this notion, we assessed the impact of CD14 deficiency on Lyme disease in C3H/HeN mice. Contrary to an anticipated diminution in pathology, CD14(-/-) mice exhibited more severe and persistent inflammation than did CD14(+/+) mice. This disparity reflects altered gene regulation within immune cells that may engender the higher bacterial burden and serum cytokine levels observed in CD14(-/-) mice. Comparing their in vitro stimulatory activity, live spirochetes, but not lysed organisms, were a potent CD14-independent stimulus of cytokine production, triggering an exaggerated response by CD14(-/-) macrophages. Collectively, our in vivo and in vitro findings support the provocative notion that: 1) pattern recognition by CD14 is entirely dispensable for elaboration of an inflammatory response to B. burgdorferi, and 2) CD14-independent signaling pathways are inherently more destructive than CD14-dependent pathways. Continued study of CD14-independent signaling pathways may provide mechanistic insight into the inflammatory processes that underlie development of chronic inflammation.

We used multiparameter flow cytometry to characterize leukocyte immunophenotypes and cytokines in skin and peripheral blood of patients with erythema migrans (EM). Dermal leukocytes and cytokines were assessed in fluids aspirated from epidermal suction blisters raised over EM lesions and skin of uninfected controls. Compared with corresponding peripheral blood, EM infiltrates were enriched for T cells, monocytes/macrophages, and dendritic cells (DCs), contained lower proportions of neutrophils, and were virtually devoid of B cells. Enhanced expression of CD14 and HLA-DR by lesional neutrophils and macrophages indicated that these innate effector cells were highly activated. Staining for CD45RO and CD27 revealed that lesional T lymphocytes were predominantly Ag-experienced cells; furthermore, a subset of circulating T cells also appeared to be neosensitized. Lesional DC subsets, CD11c(+) (monocytoid) and CD11c(-) (plasmacytoid), expressed activation/maturation surface markers. Patients with multiple EM lesions had greater symptom scores and higher serum levels of IFN-alpha, TNF-alpha, and IL-2 than patients with solitary EM. IL-6 and IFN-gamma were the predominant cytokines in EM lesions; however, greater levels of both mediators were detected in blister fluids from patients with isolated EM. Circulating monocytes displayed significant increases in surface expression of Toll-like receptor (TLR)1 and TLR2, while CD11c(+) DCs showed increased expression of TLR2 and TLR4; lesional macrophages and CD11c(+) and CD11c(-) DCs exhibited increases in expression of all three TLRs. These results demonstrate that Borrelia burgdorferi triggers innate and adaptive responses during early Lyme disease and emphasize the interdependence of these two arms of the immune response in the efforts of the host to contain spirochetal infection.

Here we examined the involvement of CD14 in monocyte activation by motile Borrelia burgdorferi and Treponema pallidum. B. burgdorferi induced secretion of IL-8 by vitamin D3-matured THP-1 cells, which was inhibited by a CD14-specific mAb known to block cellular activation by LPS and the prototypic spirochetal lipoprotein, outer surface protein A. Enhanced responsiveness to B. burgdorferi also was observed when THP-1 cells were transfected with CD14. Because borreliae within the mammalian host and in vitro-cultivated organisms express different lipoproteins, experiments also were performed with "host-adapted" spirochetes grown within dialysis membrane chambers implanted into the peritoneal cavities of rabbits. Stimulation of THP-1 cells by host-adapted organisms was CD14 dependent and, interestingly, was actually greater than that observed with in vitro-cultivated organisms grown at either 34 degrees C or following temperature shift from 23 degrees C to 37 degrees C. Consistent with previous findings that transfection of Chinese hamster ovary cells with CD14 confers responsiveness to LPS but not to outer surface protein A, B. burgdorferi failed to stimulate CD14-transfected Chinese hamster ovary cells. T. pallidum also activated THP-1 cells in a CD14-dependent manner, although its stimulatory capacity was markedly less than that of B. burgdorferi. Moreover, cell activation by motile T. pallidum was considerably less than that induced by treponemal sonicates. Taken together, these findings support the notion that lipoproteins are the principle component of intact spirochetes responsible for monocyte activation, and they indicate that surface exposure of lipoproteins is an important determinant of a spirochetal pathogen's proinflammatory capacity.