UPEC kidney infection triggers neuro-immune communication leading to modulation of local renal inflammation by splenic IFNγ.

Bacterial infection results in a veritable cascade of host responses, both local and systemic. To study the initial stages of host-pathogen interaction in living tissue we use spatially-temporally controlled in vivo models. Using this approach, we show here that within 4 h of a uropathogenic Escherichia coli (UPEC) infection in the kidney, an IFNγ response is triggered in the spleen. This rapid infection-mediated inter-organ communication was found to be transmitted via nerve signalling. Bacterial expression of the toxin α-hemolysin directly and indirectly activated sensory neurons, which were identified in the basement membrane of renal tubules. Nerve activation was transmitted via the splenic nerve, inducing upregulation of IFNγ in the marginal zones of the spleen that led to increasing concentrations of IFNγ in the circulation. We found that IFNγ modulated the inflammatory signalling generated by renal epithelia cells in response to UPEC infection. This demonstrates a new concept in the host response to kidney infection; the role of nerves in sensing infection and rapidly triggering a systemic response which can modulate inflammation at the site of infection. The interplay between the nervous and immune systems is an exciting, developing field with the appealing prospect of non-pharmaceutical interventions. Our study identifies an important role for systemic neuro-immune communication in modulating inflammation during the very first hours of a local bacterial infection in vivo

Spinal actions of lipoxin A4 and 17(R)-resolvin D1 attenuate inflammation-induced mechanical hypersensitivity and spinal TNF release.

Lipoxins and resolvins have anti-inflammatory and pro-resolving actions and accumulating evidence indicates that these lipid mediators also attenuate pain-like behavior in a number of experimental models of inflammation and tissue injury-induced pain. The present study was undertaken to assess if spinal administration of lipoxin A4 (LXA4) or 17 (R)-resolvin D1 (17(R)-RvD1) attenuates mechanical hypersensitivity in the carrageenan model of peripheral inflammation in the rat. Given the emerging role of spinal cytokines in the generation and maintenance of inflammatory pain we measured cytokine levels in the cerebrospinal fluid (CSF) after LXA4 or 17(R)-RvD1 administration, and the ability of these lipid metabolites to prevent stimuli-induced release of cytokines from cultured primary spinal astrocytes. We found that intrathecal bolus injection of LXA4 and17(R)-RvD1 attenuated inflammation-induced mechanical hypersensitivity without reducing the local inflammation. Furthermore, both LXA4 and 17(R)-RvD1 reduced carrageenan-induced tumor necrosis factor (TNF) release in the CSF, while only 17(R)-RvD1attenuated LPS and IFN-γ-induced TNF release in astrocyte cell culture. In conclusion, this study demonstrates that lipoxins and resolvins potently suppress inflammation-induced mechanical hypersensitivity, possibly by attenuating cytokine release from spinal astrocytes. The inhibitory effect of lipoxins and resolvins on spinal nociceptive processing puts them in an intriguing position in the search for novel pain therapeutics

17 (R)-RvD1 attenuate IFN-γ and LPS induced TNF induction in rat primary astrocytes.

<p>Bar graphs showing levels of TNF in media from primary rat astrocyte cultures (A) following stimulation with IFN-γ (1000 U/ml, 24 h), LPS (2 µg/ml, 24 h) or the combined effect of IFN-γ (1000 U/ml, 4 h) followed by LPS (2 µg/ml, 20 h). Pretreatment with 17(R)-RvD1 (500 nM, 30 min) significantly reduced IFN-γ (B) and LPS-induced (C)-TNF release. No significant effect was seen after pretreatment with LXA4 (500 nM, 30 min). Each bar represents mean ± S.E.M, * represents a significant difference at p<0.05 as compared to PBS (A) or indicated in the figure (B-D).</p

FPR2/ALX mRNA is present in the rat spinal cord and cultured spinal astrocytes.

<p>Bar graphs showing the expression of (A) FPR2/ALX mRNA in the rat ipsilateral spinal cord plotted versus time following carrageenan injection to the hind paw, presented as a percent of mRNA levels in control (naïve) rat spinal cord. Each bar represents the mean ± S.E.M, n= 6-10. * represents a significant difference at p<0.05 as compared with naïve spinal cord. FPR2/ALX mRNA is expressed in the rat (B) and human astrocytes (C). GPR32 mRNA is expressed in human astrocytes (C). mRNA levels are expressed as relative units and each bar represents the mean ± S.E.M for three repeats. The immunohistochemical images show the expression of FPR2/ALX (D), the astrocyte marker GFAP (E) and the colocalization of FPR2/ALX and GFAP (F) in naïve rat lumbar spinal cord.</p

17(R)-RvD1 reduced TNF-induced ERK activation in human primary astrocytes.

<p>Bar graphs and representative western blots showing MAPK phosphorylation levels in control and TNF (50 ng/ml) stimulated cells. In astrocytes, 17(R)-RvD1 (265 nM) inhibited TNF-induced ERK (A), but not p38 (B) or JNK (C) phosphorylation. Each bar represents the mean ± S.E.M for three repeats. * represents p<0.05 for comparisons indicated in the figure.</p

Intrathecal injection of LXA4 and 17(R)-RvD1 reduces carrageenan-induced mechanical hypersensitivity.

<p>Paw withdrawal thresholds plotted versus time are shown for the ipsilateral (A, D) and contralateral (C, F) hind paw following carrageenan administration. Intrathecal pretreatment with LXA4 (A) or 17(R)-RvD1 (D) reduced mechanical hypersensitivity as compared to vehicle, while i.t. injection of LXA4 (C) or 17(R)-RvD1 (F) had no effect on mechanical thresholds in the contralateral (non-inflamed) hind paw. The hyperalgesic index (see material and methods) calculated for 0–6 h was significantly reduced by LXA4 (B) and 17(R)-RvD1 (E) pretreatment. All data are presented as mean ± S.E.M, * represents a significant difference at p<0.05 as compared with i.t. vehicle.</p

Intrathecal injection of LXA4 and 17(R)-RvD1 does not change carrageenan-induced inflammation.

<p>Bar graphs show that the increased paw size measured 4 h following carrageenan injection was not altered by pretreatment with LXA4 (A) or 17(R)-RvD1 (B) as compared to pretreatment with vehicle. All data are presented as mean ± S.E.M, * represents a significant difference at p<0.05 as compared with i.t. vehicle.</p

Cartilage-binding antibodies induce pain through immune complex-mediated activation of neurons

Rheumatoid arthritis-associated joint pain is frequently observed independent of disease activity, suggesting unidentified pain mechanisms. We demonstrate that antibodies binding to cartilage, specific for collagen type II (CII) or cartilage oligomeric matrix protein (COMP), elicit mechanical hypersensitivity in mice, uncoupled from visual, histological and molecular indications of inflammation. Cartilage antibody-induced pain-like behavior does not depend on complement activation or joint inflammation, but instead on tissue antigen recognition and local immune complex (IC) formation. smFISH and IHC suggest that neuronal Fcgr1 and Fcgr2b mRNA are transported to peripheral ends of primary afferents. CII-ICs directly activate cultured WT but not FcR gamma chain-deficient DRG neurons. In line with this observation, CII-IC does not induce mechanical hypersensitivity in FcR gamma chain-deficient mice. Furthermore, injection of CII antibodies does not generate pain-like behavior in FcR gamma chain-deficient mice or mice lacking activating Fc gamma Rs in neurons. In summary, this study defines functional coupling between autoantibodies and pain transmission that may facilitate the development of new disease-relevant pain therapeutics