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Departments of
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Internal Medicine and
Microbiology and the
Cell and Molecular Biology Graduate Program, University of Texas Southwestern Medical Center, Dallas, TX 75235; and
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Maxwell Finland Laboratory for Infectious Diseases, Boston University School of Medicine/Boston Medical Center, Boston, MA 02118
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The well characterized LPS receptor, CD14, has been described as a pattern recognition molecule for diverse bacterial components that trigger innate immune responses (16, 17, 18). CD14 exists as a 55-kDa glycosylphosphatidylinositol-linked protein (membrane CD14 (mCD14)4) on the surface of macrophages and neutrophils (19, 20, 21) and as a soluble protein (sCD14) in serum (22). The soluble form of CD14 facilitates the activation of cells, such as endothelial cells, which lack mCD14 (23, 24). Recent in vitro studies implicate both forms of CD14 in the inflammatory response to spirochetal lipoproteins, although there appear to be distinctions between the CD14-dependent pathways used by LPS and spirochetal lipoproteins (25, 26, 27). The lipid moiety of lipoproteins is crucial for binding to CD14 as well as for cell activation (12, 27). However, an apparent paradox arises from the fact that these lipid components are sequestered within the spirochetal membrane (28), where they should be inaccessible for binding to CD14. Topological concerns are even more pertinent with T. pallidum, as evidence to date indicates that it has a paucity of lipoproteins on its surface (29, 30). Nevertheless, motile B. burgdorferi and T. pallidum do activate innate immune effector cells (31, 32, 33), although it remains to be proven that these effects are lipoprotein-mediated.
As an initial step toward addressing this issue, and to employ in vitro conditions that more closely resemble the in vivo situation, we examined monocyte activation by motile B. burgdorferi and T. pallidum. The findings reported here indicate that CD14 does indeed facilitate monocyte activation by spirochetes, and they also support the hypothesis that lipoproteins are the principle component of intact organisms in this process. Also of considerable interest was the observation that surface exposure of lipoproteins is an important determinant of a spirochetal pathogen’s stimulatory capacity. With this information, we are better positioned to understand how pathogenic spirochetes engage host immune defenses during infection.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Salmonella minnesota R5 LPS (Sigma, St. Louis, MO) was suspended in 0.1% triethylamine adjusted to pH 8.0 with 100 mM Tris-HCl. Dilutions of LPS were made with HNEB buffer (20 mM HEPES, pH 7.4, 150 mM NaCl, 0.1 mM EDTA, and 0.03% BSA). 1,25-dihydroxyvitamin D3 was obtained from Biomol Research Laboratories (Plymouth Meeting, PA). G-418 sulfate was purchased from Mediatech (Herndon, VA). Great care was taken during the preparation of all buffers and reagents to minimize contamination with environmental LPS by using baked glassware, disposable plasticware, and pyrogen-free H2O.
Bacterial strains
Low-passage B. burgdorferi 297 (34) was obtained from Russell Johnson (University of Minnesota). The B31-type strain of B. burgdorferi MedImmune clone (4) was provided by Raju Lathigra (MedImmune, Gaithersburg, MD). Spirochetes were cultivated in vitro at 23°C, 34°C, or 37°C after temperature shift from 23°C as described previously (35). All experiments were performed with spirochetes that had been passaged no more than five times in Barbour-Stoenner-Kelly (BSK)-H medium (Sigma). With both strains, infectivity was periodically assessed by low-dose (1 x 103 borreliae) intradermal needle inoculation of 3-wk-old C3H/HeJ mice (The Jackson Laboratory, Bar Harbour, ME) and culture of ear punch biopsies 2 wk later. T. pallidum (Nichols) was propagated by intratesticular inoculation of adult New Zealand White rabbits as previously described (36). Treponemes were extracted from infected testes in RPMI 1640 medium (Mediatech) supplemented with 10% heat-inactivated FBS (heated for 30 min at 56°C) (Mediatech) and separated from testicular tissue debris by low-speed centrifugation (350 x g for 10 min). In all experiments, spirochetes were enumerated by dark-field microscopy using a Petroff Hausser counting chamber (Hausser Scientific Company, Horsham, PA).
Cultivation of B. burgdorferi B31 within dialysis membrane chambers (DMCs) implanted into rabbits
To generate increased quantities of host-adapted spirochetes, we modified the procedure of Akins et al. (37). Briefly, Spectra/Por 6 dialysis membranes (Fisher Scientific, Pittsburgh, PA) with a molecular mass cut-off of 8000 Da were prewashed with Milli-Q water and sterilized by boiling in 1 mM EDTA and then in Milli-Q water for 20 min each. Dialysis bags were submersed in BSK-H medium overnight at 4°C. After tying one end, each bag was filled with 25 ml of BSK-H medium containing 2.5 x 104 organisms from a mid-log phase culture grown at 23°C. Tubing was then tied and excess membrane was removed from both ends. New Zealand White rabbits were anesthetized with 3.5% isoflurane, and three DMCs per rabbit were implanted into the peritoneal cavities using strict aseptic technique. Eight to 10 days postimplantation, the chambers were harvested. The outside of each chamber was washed extensively with BSK-H medium and the contents were removed via syringe aspiration.
Purification of native outer surface protein A (nOspA) from B. burgdorferi
NOspA was affinity purified from B. burgdorferi
strain TI1-EV as previously described (38) and stored in
33 mM Tris, pH 7.4, 1.6 mM NaCl, and 20 mM
n-octyl-ß-glucoside at -70°C. Preparations of nOspA
contained 
12 pg LPS/µg protein as measured by the QCL-1000
quantitative, chromogenic Limulus amebocyte lysate assay
(BioWhittaker, Walkersville, MD).
SDS-PAGE and two-dimensional nonequilibrium pH gel electrophoresis (2D-NEPHGE)
For SDS-PAGE, samples were boiled for 5 min in final sample buffer (62.5 mM Tris-HCl, 2% SDS, 10% glycerol, 5% 2-ME, 0.001% bromophenol blue) and electrophoresed through 4.5% stacking and 12.5% resolving gels before staining with silver. 2D-NEPHGE was performed as described by O’Farrell et al. (39). Briefly, whole-cell lysates were subjected to first dimension NEPHGE for 5 h at 400 V in 11-cm tube gels consisting of 4% pH 5–7 and 1% pH 3.5–10 ampholines (Bio-Rad, Hercules, CA). For the second dimension, tube gels were overlaid on top of 2.4% stacking and 12.5% separating SDS-polyacrylamide slab gels. Apparent isoelectric point (pI) values were determined by adding pI standards (Bio-Rad) to one tube gel and subjecting it to first- and second-dimension electrophoresis under the same conditions.
Cell lines
The human promyelomonocytic cell line THP-1 (40)
was maintained in RPMI 1640 medium (Mediatech) containing 2 mM
L-glutamine and supplemented with 10% heat-inactivated
FBS, 100 U of penicillin per ml, and 100 µg of streptomycin per ml.
Cells were differentiated by preincubation with 100 nM vitamin
D3 for 72–96 h before stimulation by LPS, nOspA,
B. burgdorferi, and T. pallidum. CD14- and Rous
sarcoma virus vector-transfected THP-1 cells (26, 41),
kindly provided by Richard Ulevitch (Scripps, La Jolla, CA), were
cultured in the continuous presence of 0.5 mg/ml (active drug) of the
aminoglycoside G-418 sulfate to ensure the maintenance of stably
transfected DNA conferring neomycin resistance. G-418 sulfate was
removed 24 h before experimentation. Chinese hamster ovary (CHO)
K1 cells stably cotransfected with pCEP4 (Invitrogen, San Diego, CA),
which constitutively expressed the gene for human CD14 from a CMV
promoter, and pUMS(ELAM)-Tac, which contains the gene for CD25 under
the control of an NF-
B-inducible E-selectin promoter (3E10 cells)
(42), were grown in Ham’s F12 medium containing 10%
heat-inactivated FBS and 400 U of hygromycin B per ml.
Cell activation experiments
THP-1 cells were seeded in 24-well flat-bottom tissue culture
plates (Becton Dickinson Labware, Lincoln Park, NJ) at a density of
2.5 x 105 cells/ml and were maintained at
37°C in a humidified atmosphere of 5% CO2 and
air. Cells were then stimulated for 3 h with LPS, nOspA, B.
burgdorferi, or T. pallidum, and culture supernatants
were assayed for IL-8 using the Duoset ELISA development system from
R&D Systems (Minneapolis, MN). For Ab blocking experiments, vitamin
D3-matured THP-1 cells (2.5 x
105 cells in 0.1 ml) were preincubated at room
temperature for 15 min with 10 µg/ml of murine mAbs directed against
CD14 (60bca and 63D3; both IgG1) before the addition of agonists. For
sonication experiments, T. pallidum were washed twice in
PBS, pH 7.2, and ruptured with a sonic dismembrator (Fisher
Scientific); the efficiency of sonication was verified by dark-field
microscopy. For analyzing cell activation by B. burgdorferi
and T. pallidum based upon total protein content, equivalent
numbers of organisms were sonicated as described above and protein
concentrations were determined using the Bio-Rad protein assay
(Bio-Rad). 3E10 cells were seeded at a density of 2 x
105 cells per well in 24-well plates; the
following day cells were washed twice with medium and stimulated for
8 h with 100 ng/ml of LPS, 1 µg/ml of nOspA, or graded ratios of
B. burgdorferi B31. The cells were then washed and incubated
with PE-conjugated mAb directed against human CD25 (Becton Dickinson
Immunocytometry Systems, San Jose, CA) for FACS analysis. In all
activation and blocking experiments, spirochetes were 
90% viable
(i.e., motile) at the end of the experiment, as assessed by dark-field
microscopy.
Statistics
The two-tailed Student’s t test or a one-way ANOVA
with a Tukey-Kramer multiple comparisons post test was performed using
GraphPad InStat version 3.00 for Windows 95 (GraphPad Software, San
Diego, CA). A value of p < 0.05 was used as the 
value to determine statistical significance for all analyses.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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In a previous study (26), functional blockade of CD14
by polyclonal anti-CD14 Abs was one of several strategies used to
demonstrate that monocytic cell activation by spirochetal lipoproteins
is facilitated by CD14. To correlate lipoprotein- and
spirochete-mediated activation, we reasoned that it would be useful to
determine whether both interact with the same domain on CD14. Recently,
two groups have independently shown that anti-CD14 mAb 60bca, which
is known to block LPS-mediated monocytic and endothelial cell
activation, also blocks cellular activation by borrelial lipoproteins
(25, 27). In preliminary studies, we also observed that
this Ab blocked secretion of the neutrophil chemoattractant IL-8 by
vitamin D3-matured THP-1 cells over a range of
nOspA concentrations, whereas 63D3, a known LPS-nonblocking mAb
(43), was without effect (data not shown). We next
examined the ability of virulent B. burgdorferi to stimulate
vitamin D3-matured cells. As shown in Fig. 1
A, B. burgdorferi
induced the secretion of IL-8 in a dose-dependent fashion; significant
cellular activation occurred with a single spirochete per cell.
Interestingly, activation of undifferentiated cells was observed at
spirochete-to-cell ratios of 100:1 and 1000:1, although the IL-8 levels
were significantly less than those produced by vitamin
D3-matured cells under the same conditions. Thus,
cellular activation by B. burgdorferi also may have a
CD14-independent component, a phenomenon previously observed at
relatively high concentrations of spirochetal lipoprotein/lipopeptide
agonists (26). Activation of vitamin
D3-matured cells by B. burgdorferi was
substantially blocked by 60bca, whereas 63D3 was noninhbitory (Fig. 1B), thereby demonstrating that the cellular response at
this spirochete-to-cell ratio (10:1) was largely CD14 dependent. The
inability of the Ab to completely block IL-8 production also was
consistent with the notion of the existence of a minor CD14-independent
component. We previously demonstrated that transfection of
undifferentiated THP-1 cells with CD14 confers enhanced responsiveness
to spirochetal lipoproteins as well as to LPS (26). To
confirm the Ab blocking results, we investigated whether CD14
transfected THP-1 cells also manifest enhanced responsiveness to live
spirochetes. Fig. 2 shows that at
spirochete-to-cell ratios above 1:1, the CD14-transfected cells
produced significantly greater amounts of IL-8 than did cells
transfected with the empty vector. As before, a lesser degree of
stimulation was observed in the absence of CD14 expression.
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Because the antigenic composition of B. burgdorferi
during mammalian infection differs from that of in vitro-cultivated
organisms (35, 44), experiments performed with in
vitro-cultivated spirochetes may not accurately reproduce pathogen-host
cell interactions occurring in vivo. Recently, we showed that
cultivation of spirochetes within DMCs implanted into the peritoneal
cavities of rats generates spirochetes that more closely resemble the
host-adapted phenotype (37). Therefore, it was of
considerable interest to compare monocytic cell activation by chamber-
and in vitro-grown organisms. To obtain the numbers of host-adapted
spirochetes required for these studies, we modified our original system
by cultivating borreliae within DMCs implanted into rabbits. Fig. 3 demonstrates that rabbit DMC-cultivated
B. burgdorferi B31 expressed greatly diminished amounts of
OspA and OspB and greatly increased amounts of OspC when compared with
organisms grown in BSK-H at 34°C or following temperature shift from
23°C to 37°C (a control for the higher ambient temperature within
the rabbit peritoneal cavity). Furthermore, as previously described for
B. burgdorferi 297 (37), other differences in
polypeptide composition were readily discernible by both SDS-PAGE (Fig. 3) and 2D-NEPHGE analysis (data not shown). Spirochetes cultivated at
34°C or following temperature shift induced similar levels of IL-8
secretion by vitamin D3-matured THP-1 cells, and
these levels were roughly equivalent to those observed in earlier
experiments with in vitro-cultivated B. burgdorferi 297
(compare Fig. 1
A and Fig. 4A). In contrast,
DMC-cultivated organisms stimulated significantly greater IL-8
secretion than either population of in vitro-cultivated organisms (Fig. 4A). To assess the contribution of CD14 to this response,
blocking experiments were performed with mAbs 60bca and 63D3. Fig. 4B shows that 60bca reduced IL-8 secretion to the levels
typically observed with undifferentiated cells, whereas 63D3 was
noninhibitory.
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Unlike THP-1 cells, tranfection of CHO cells with CD14 does not
confer responsiveness to spirochetal lipoproteins as it does to LPS
(26). This important observation was one of several lines
of evidence suggesting that spirochetal lipoproteins and LPS use
disparate transmembrane signaling elements immediately downstream from
CD14 (11, 12, 38). In light of the above findings with
CD14-transfected THP-1 cells, we next sought to determine the effect of
CD14 transfection on the responsiveness of CHO cells to live
spirochetes. For these experiments, we used a CHO cell line
cotransfected with CD14 (expressed constitutively) and the Tac Ag
(CD25) under the control of the NF-B-inducible E-selectin promoter
(3E10 cells) (42). In contrast to LPS, both B.
burgdorferi and nOspA failed to induce the expression of CD25 in
3E10 cells (Fig. 5).
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T. pallidum is similar to B. burgdorferi in
that it contains abundant lipoproteins capable of activating monocytic
cells in a CD14-enhanced fashion (11, 12, 26, 38).
However, unlike B. burgdorferi, T. pallidum
lipoproteins are predominantly subsurface (29, 30) and
thus may not be as accessible to CD14 as their borrelial counterparts.
To address this issue, we examined the ability of motile T.
pallidum to stimulate THP-1 cells. Activation of vitamin
D3-matured cells was observed only at 1000
treponemes per cell (Fig. 6A);
blocking with mAb 60bca confirmed that this response was facilitated by
CD14 (Fig. 6B). Comparison of Figs. 1A and
6A highlights the much lower stimulatory capacity of
T. pallidum as compared with B. burgdorferi. We
next considered the possibility that the difference in IL-8 secretion
induced by the two spirochetes was due to the larger size of B.
burgdorferi rather than to their different molecular
architectures. To evaluate this, experiments were conducted in which
the input spirochete-to-cell ratios were plotted by protein content. As
shown in Fig. 7A, B.
burgdorferi was more stimulatory than T. pallidum over
the entire range of protein concentrations evaluated. If the relatively
poor stimulatory activity of T. pallidum were due to its
paucity of surface-exposed lipoproteins, one would predict that
T. pallidum sonicates would be more stimulatory than intact
organisms. As shown in Fig. 7B, this was indeed the case
when IL-8 secretion induced by intact treponemes and equivalent cell
lysates was directly compared. It is noteworthy that the cellular
response to treponemal sonicate plateaus at ratios above 10
organisms/cell; a plateau in responsiveness also was observed when
purified lipoproteins or synthetic/lipopeptides were used in
stimulation assays (26).
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Here we used two different approaches to demonstrate that induction of IL-8 secretion by monocytic cells during incubation with viable spirochetes is facilitated by CD14. The first used vitamin D3-matured THP-1 cells. Previous studies have shown that vitamin D3 maturation induces expression of surface-bound CD14 and that this results in enhanced cellular responsiveness to both LPS and spirochetal lipoproteins (26, 38, 46, 47). Because the effects of vitamin D3 are pleiotropic (48, 49), we confirmed the CD14 dependence of the response with a LPS-blocking anti-CD14 mAb, which also antagonized cellular activation by the prototypical spirochetal lipoprotein OspA (25, 27). Although the epitope on CD14 recognized by 60bca has not been mapped to a specific region of CD14 required for LPS-mediated signaling (50, 51, 52), this result is consistent with the finding that LPS and nOspA appear to bind to similar domains on CD14 (27). To confirm the blocking studies, we also examined THP-1 cells transfected with CD14; as previously observed with lipoproteins/lipopeptides (26), responsiveness was significantly enhanced in the transfected cells. Lastly, we noted that CHO cells transfected with CD14, while sensitive to LPS, failed to respond to either spirochetes or nOspA, indicating that both spirochetes and nOspA use a CD14-dependent signaling pathway(s) different from that used by LPS. Although these results do not constitute definitive evidence that lipoproteins are the principal stimulatory component of live spirochetes, they are entirely consistent with this notion.
Lipid modification is essential for CD14-dependent lipoprotein activation and probably reflects binding of the agonist to an amphipathic pocket within the receptor. However, because the lipid moieties of lipoproteins are stably embedded within the spirochetal membrane (28), it is not immediately clear how this binding interaction occurs. At least three testable scenarios, which are not mutually exclusive, can be envisioned to explain this apparent paradox. The first is that lipoproteins shed from the surface of the bacterium or released from dying organisms bind to CD14 and activate the cell. If this is correct, then binding of the spirochete to the monocytic cell surface should not be necessary for activation. Second, lipoproteins may be directly removed from the spirochetal membrane, thereby overcoming a thermodynamically stable configuration within the lipid bilayer. This process also might not require direct spirochete-cell interactions; alternatively, outer membrane perturbations caused when organisms bind to the monocytic cell surface could facilitate transfer of lipoproteins to CD14. Lastly, degradation of lipoproteins following uptake of spirochetes into phagolysosomes could liberate biologically active lipopeptides, which then interact with CD14. Consistent with this notion are the observations that synthetic lipopeptides and lipopeptides generated by extensive proteolysis of native proteins retain proinflammatory activity (11, 12, 27) and that CD14 is found within endocytic structures (53). Interestingly, a similar topologic problem pertains to LPS given that its biologically active component, lipid A, also is stably inserted into Gram-negative bacterial outer membranes (54). Although the mechanism by which outer membrane-associated LPS engages CD14 has not been elucidated, studies suggest that it may be more potent for signaling than free LPS (55, 56). Ongoing efforts to distinguish among these mechanisms with respect to spirochetal lipoproteins could have broader implications for other disorders, including Gram-negative bacterial sepsis and septic shock (57).
The topological considerations for T. pallidum are even more complex given its paucity of surface-exposed lipoproteins (29, 30). In head-to-head comparisons, purified T. pallidum cell lysates, lipoproteins, and synthetic lipopeptides are similar in potency to each other and to their borrelial counterparts (11, 12, 26). On the other hand, the in vitro experiments reported here clearly demonstrate that intact treponemes are markedly less stimulatory than either treponemal sonicates or intact B. burgdorferi and that differences in cell activation between T. pallidum and B. burgdorferi could not be attributed to the larger size of the latter. We believe that the disparate outer membrane architectures of the two organisms is the most straightforward explanation for their inherently different stimulatory capacities. It should be noted that these findings also lend additional, albeit indirect, support to the conjecture that lipoproteins are responsible for monocyte activation by intact spirochetes. Two additional implications of the disparity between T. pallidum and B. burgdorferi need to be mentioned. First, compared with B. burgdorferi, cellular activation by T. pallidum should be relatively dependent upon uptake and processing by professional phagocytes. Second, although constitutional manifestations occur with both syphilis and Lyme disease (1, 2), there is a general impression that they are more common and severe in Lyme disease despite its paucibacillary nature (2, 34, 58). A greater ability of intact borreliae to induce cytokine production by innate immune effector cells could underlie, at least in part, this clinical observation. T. pallidum’s ability to evade phagocytosis by macrophages, even in the presence of opsonizing Abs (30, 59, 60), would further serve to diminish cytokine production during syphilitic infection.
T. pallidum exists only within a mammalian host and, therefore, is perpetually host adapted. Consequently, one can be highly certain that in vitro experiments with the syphilis spirochete are examining the bacterium in the antigenic state actually encountered by the host during infection. B. burgdorferi, on the other hand, undergoes major shifts in antigenic composition as it cycles between arthropod and mammal (35, 44). Based upon their expression of proteins such as OspA, OspB, and Lp6.6 and their decreased expression of OspC, in vitro-cultivated organisms appear to more closely resemble the phenotype within ticks. These considerations sound a cautionary note regarding tissue culture studies conducted with in vitro-cultivated organisms. To circumvent this problem, we also conducted studies with DMC-grown organisms; surprisingly, we found that spirochetes cultivated in this manner were actually more stimulatory than their in vitro-grown counterparts. Although these host-adapted organisms expressed much lower levels of OspA and OspB, the up-regulation of other lipoprotein Ags, most notably OspC, probably explains their greater stimulatory capacity. This finding also potentially relates to the prominence of constitutional symptoms in Lyme disease (2).
For many years it has been postulated that a transmembrane protein immediately downstream from CD14 transduces the signal from this glycosylphosphatidylinositol-linked polypeptide after binding of LPS or other agonists (18, 61). Recent findings implicate one or more members of the Toll-like receptor (TLR) protein family as the long-sought signaling element(s) (62, 63, 64, 65, 66). Our current working hypothesis is that the use of different TLR proteins explains the previously observed dichotomy between LPS- and lipoprotein-mediated CD14-dependent signaling (26). The use of different TLRs as downstream signaling elements provides a potential explanation for other observations made by us here and in a prior communication (26). For example, it predicts that CHO cells constitutively express the LPS-specific TLR but not that used by spirochetal lipoproteins, thereby accounting for the lack of responsiveness of CD14-transfected CHO cells to lipoproteins and spirochetes. Furthermore, the consistently greater responsiveness of vitamin D3-matured THP-1 cells, as compared with CD14-transfected THP-1 cells, could reflect vitamin D3-induced expression of TLRs as well as CD14. Lastly, the CD14-independent activation observed with either higher dosages of lipoproteins/lipopeptides (26) or higher spirochete-to-cell ratios could reflect the bypassing of CD14 in favor of a direct interaction with one or more TLRs. On the other hand, the possibility also exists that activation of undifferentiated THP-1 cells reflects a distinct signaling pathway. Examination of the role of TLRs in these signaling events will enable us to address the above issues while further exploring the relationship(s) between lipoprotein- and spirochete-mediated cellular activation.
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Acknowledgments |
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Footnotes |
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2 T.J.S. and D.A.B. contributed equally to this work.
3 Address correspondence and reprint requests to Dr. Justin D. Radolf, Center for Microbial Pathogenesis, University of Connecticut Health Center, Farmington, CT 06030. E-mail address:
4 Abbreviations used in this paper: mCD14, membrane CD14; nOspA, native outer surface protein A; CHO, Chinese hamster ovary; BSK, Barbour-Stoenner-Kelly; DMCs, dialysis membrane chambers; sCD14, soluble CD14; 3E10, CHO-CD14-Tac reporter cell line; 2D-NEPHGE, two-dimensional nonequilibrium pH gel electrophoresis; TLRs, Toll-like receptors.
Received for publication March 12, 1999. Accepted for publication May 27, 1999.
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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T cells respond to Borrelial burgdorferi lipoproteins and lipidated hexapeptides. J. Immunol. 161:5762. by Borrelia burgdorferi. Infect. Immun. 60:1109.B. Infect. Immun. 64:3845.[Abstract]
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 M. Hashimoto, Y. Asai, and T. Ogawa Treponemal Phospholipids Inhibit Innate Immune Responses Induced by Pathogen-associated Molecular Patterns J. Biol. Chem., November 7, 2003; 278(45): 44205 - 44213. [Abstract] [Full Text] [PDF]
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J. L. Coleman and J. L. Benach The Urokinase Receptor Can Be Induced by Borrelia burgdorferi through Receptors of the Innate Immune System Infect. Immun., October 1, 2003; 71(10): 5556 - 5564. [Abstract] [Full Text] [PDF]
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 W. C. Van Voorhis, L. K. Barrett, S. A. Lukehart, B. Schmidt, M. Schriefer, and C. E. Cameron Serodiagnosis of Syphilis: Antibodies to Recombinant Tp0453, Tp92, and Gpd Proteins Are Sensitive and Specific Indicators of Infection by Treponema pallidum J. Clin. Microbiol., August 1, 2003; 41(8): 3668 - 3674. [Abstract] [Full Text] [PDF]
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J. Anguita, S. W. Barthold, R. Persinski, M. N. Hedrick, C. A. Huy, R. J. Davis, R. A. Flavell, and E. Fikrig Murine Lyme Arthritis Development Mediated by p38 Mitogen-Activated Protein Kinase Activity J. Immunol., June 15, 2002; 168(12): 6352 - 6357. [Abstract] [Full Text] [PDF]
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R. N. Fichorova, A. O. Cronin, E. Lien, D. J. Anderson, and R. R. Ingalls Response to Neisseria gonorrhoeae by Cervicovaginal Epithelial Cells Occurs in the Absence of Toll-Like Receptor 4-Mediated Signaling J. Immunol., March 1, 2002; 168(5): 2424 - 2432. [Abstract] [Full Text] [PDF]
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D. A. Bouis, T. G. Popova, A. Takashima, and M. V. Norgard Dendritic Cells Phagocytose and Are Activated by Treponema pallidum Infect. Immun., January 1, 2001; 69(1): 518 - 528. [Abstract] [Full Text] [PDF]
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P. K. Murthy, V. A. Dennis, B. L. Lasater, and M. T. Philipp Interleukin-10 Modulates Proinflammatory Cytokines in the Human Monocytic Cell Line THP-1 Stimulated with Borrelia burgdorferi Lipoproteins Infect. Immun., December 1, 2000; 68(12): 6663 - 6669. [Abstract] [Full Text] [PDF]
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K.-i. Shibata, A. Hasebe, T. Into, M. Yamada, and T. Watanabe The N-Terminal Lipopeptide of a 44-kDa Membrane-Bound Lipoprotein of Mycoplasma salivarium Is Responsible for the Expression of Intercellular Adhesion Molecule-1 on the Cell Surface of Normal Human Gingival Fibroblasts J. Immunol., December 1, 2000; 165(11): 6538 - 6544. [Abstract] [Full Text] [PDF]
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E. Lorenz, J. P. Mira, K. L. Cornish, N. C. Arbour, and D. A. Schwartz A Novel Polymorphism in the Toll-Like Receptor 2 Gene and Its Potential Association with Staphylococcal Infection Infect. Immun., November 1, 2000; 68(11): 6398 - 6401. [Abstract] [Full Text] [PDF]
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E. Lien, T. J. Sellati, A. Yoshimura, T. H. Flo, G. Rawadi, R. W. Finberg, J. D. Carroll, T. Espevik, R. R. Ingalls, J. D. Radolf, et al. Toll-like Receptor 2 Functions as a Pattern Recognition Receptor for Diverse Bacterial Products J. Biol. Chem., November 19, 1999; 274(47): 33419 - 33425. [Abstract] [Full Text] [PDF]
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B. Opitz, N. W. J. Schroder, I. Spreitzer, K. S. Michelsen, C. J. Kirschning, W. Hallatschek, U. Zahringer, T. Hartung, U. B. Gobel, and R. R. Schumann Toll-like Receptor-2 Mediates Treponema Glycolipid and Lipoteichoic Acid-induced NF-kappa B Translocation J. Biol. Chem., June 15, 2001; 276(25): 22041 - 22047. [Abstract] [Full Text] [PDF]
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