Signaling through CD14 Attenuates the Inflammatory Response toBorrelia burgdorferi, the Agent of Lyme Disease

Abstract

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.

NKT cells prevent chronic joint inflammation after infection withBorrelia burgdorferi

“…), as previously described (29). In 2 independent experiments, shown separately as A and B, little increase in joint thickness above baseline was observed in either J␣18 ϩ/ϩ or J␣18 Ϫ/Ϫ mice for the first 14 (Fig.…”

“…In some studies (2,5,29), severe and prolonged inflammation correlated with decreased clearance of B. burgdorferi. Therefore, we compared spirochete burden in the tissues of wild-type and J␣18 Ϫ/Ϫ mice by quantitative (q)PCR, by using the spirochetal flaB gene as a target.…”

“…The amount of polymorphonuclear and mononuclear cell infiltration was graded in a blinded manner as 0 (none), 1 (light), 2 (moderate), or 3 (heavy). Hearts from the same time points also were evaluated for histopathological alterations as previously described (29).…”

“…Joint inflammation was evaluated (i) grossly by digital caliper measurement of tibiotarsal joint thickness, and (ii) histologically by examination of decalcified, paraffin-embedded specimens stained with hematoxylin and eosin. Disease severity was assessed on the basis of edema, inflammatory cell infiltration, and thickening of the tendon sheath as previously described (29). The amount of polymorphonuclear and mononuclear cell infiltration was graded in a blinded manner as 0 (none), 1 (light), 2 (moderate), or 3 (heavy).…”

“…Quantification of B. burgdorferi DNA was performed by qPCR by using TaqMan Universal PCR Master Mix and the iQ5 real-time PCR Detection System (BIO-RAD Laboratories). Genomic DNA was extracted and qPCR was performed in triplicate by using 40 ng of target DNA, along with B. burgdorferi-specific flaB primers (200 nM) and probe (320 nM) or primers (400 nM) and probe (320 nM) directed against the single-copy mouse nidogen gene and quantification of target DNA was accomplished as described previously (29).…”