Stimulation of toll-like receptor 2 by Coxiella burnetii is required for macrophage production of pro-inflammatory cytokines and resistance to infection.
Innate and adaptive immune responses are initiated upon recognition of microbial molecules by Toll-like receptors (TLRs). We have investigated the importance of these receptors in the induction of pro-inflammatory cytokines and macrophage resistance to infection with Coxiella burnetii, an obligate intracellular bacterium and the etiological agent of Q fever. By using a Chinese hamster ovary/CD14 cell line expressing either functional TLR2 or TLR4, we determined that C. burnetii phase II activates TLR2 but not TLR4. Macrophages deficient for TLR2, but not TLR4, produced less tumor necrosis factor-alpha and interleukin-12 upon C. burnetii infection. Furthermore, it was found that TLR2 activation interfered with C. burnetii intracellular replication, as macrophages from TLR2-deficient mice were highly permissive for C. burnetii growth compared with macrophages from wild type mice or TLR4-deficient mice. Although LPS modifications distinguish virulent C. burnetii phase I bacteria from avirulent phase II organisms, electrospray ionization-mass spectrometry analysis showed that the lipid A moieties isolated from these two phase variants are identical. Purified lipid A derived from either phase I or phase II LPS failed to activate TLR2 and TLR4. Indeed, the lipid A molecules were able to interfere with TLR4 signaling in response to purified Escherichia coli LPS. These studies indicate that TLR2 is an important host determinant that mediates recognition of C. burnetii and a response that limits growth of this intracellular pathogen.
Section of Microbial Pathogenesis, Yale University School of Medicine, New Haven, Connecticut 06536, USA. dario.zamboni@yale.edu
Dario S
DS
Zamboni
Marco A
MA
Campos
Ana C T
AC
Torrecilhas
Kati
K
Kiss
James E
JE
Samuel
Douglas T
DT
Golenbock
Fanny N
FN
Lauw
Craig R
CR
Roy
Igor C
IC
Almeida
Ricardo T
RT
Gazzinelli
D000818:Animals; D001424:Bacterial Infections / Q000276:immunology*; D016466:CHO Cells; D016997:Coxiella burnetii / Q000737:chemistry / Q000254:growth & development / Q000276:immunology*; D006224:Cricetinae; D016207:Cytokines / Q000096:biosynthesis*; D004926:Escherichia coli; D005434:Flow Cytometry; D015870:Gene Expression; D007249:Inflammation / Q000276:immunology*; D018664:Interleukin-12 / Q000096:biosynthesis; D008050:Lipid A / Q000032:analysis; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000276:immunology* / Q000382:microbiology; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D009154:Mutation; D011956:Receptors, Cell Surface / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D015375:Receptors, Interleukin-2 / Q000032:analysis; D015398:Signal Transduction; D021241:Spectrometry, Mass, Electrospray Ionization; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis
D016207:Cytokines; D008050:Lipid A; D008070:Lipopolysaccharides; D011956:Receptors, Cell Surface; D015375:Receptors, Interleukin-2; C493486:Tlr2 protein, mouse; C493487:Tlr4 protein, mouse; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha; D018664:Interleukin-12