Christopher C. M. Waterhouse

Intravascular Danger Signals Guide Neutrophils to Sites of Sterile Inflammation

Inflammation Response in Living Color Besides responding to microbial infection, our immune system also plays an important role in responding to sterile injury, for example, during trauma or organ necrosis. In a mouse model of sterile liver inflammation, McDonald et al. (p. 362) used dynamic in vivo imaging to visualize the innate immune response, which is dominated by neutrophils. Neutrophils were rapidly recruited to the site of inflammation through intravascular channels. Adenosine triphosphate generated from necrotic cells at the injury site and the Nlrp3 inflammasome were required for neutrophils to exit the circulation into the vascular endothelium, where they used integrins to adhere. A luminal chemokine gradient guided integrin-dependent, intravascular migration toward the site of injury. Finally, formyl peptides provided a signal to override the chemokine gradient and draw neutrophils into the site of injury. In vivo dynamic imaging reveals the underlying mechanisms of recruitment of neutrophils into injured tissue. Neutrophils are recruited from the blood to sites of sterile inflammation, where they contribute to wound healing but may also cause tissue damage. By using spinning disk confocal intravital microscopy, we examined the kinetics and molecular mechanisms of neutrophil recruitment to sites of focal hepatic necrosis in vivo. Adenosine triphosphate released from necrotic cells activated the Nlrp3 inflammasome to generate an inflammatory microenvironment that alerted circulating neutrophils to adhere within liver sinusoids. Subsequently, generation of an intravascular chemokine gradient directed neutrophil migration through healthy tissue toward foci of damage. Lastly, formyl-peptide signals released from necrotic cells guided neutrophils through nonperfused sinusoids into the injury. Thus, dynamic in vivo imaging revealed a multistep hierarchy of directional cues that guide neutrophil localization to sites of sterile inflammation.

A new genetic subgroup of chronic granulomatous disease with autosomal recessive mutations in p40phox and selective defects in neutrophil NADPH oxidase activity

Chronic granulomatous disease (CGD), an immunodeficiency with recurrent pyogenic infections and granulomatous inflammation, results from loss of phagocyte superoxide production by recessive mutations in any 1 of 4 genes encoding subunits of the phagocyte NADPH oxidase. These include gp91(phox) and p22(phox), which form the membrane-integrated flavocytochrome b, and cytosolic subunits p47(phox) and p67(phox). A fifth subunit, p40(phox), plays an important role in phagocytosis-induced superoxide production via a phox homology (PX) domain that binds to phosphatidylinositol 3-phosphate (PtdIns(3)P). We report the first case of autosomal recessive mutations in NCF4, the gene encoding p40(phox), in a boy who presented with granulomatous colitis. His neutrophils showed a substantial defect in intracellular superoxide production during phagocytosis, whereas extracellular release of superoxide elicited by phorbol ester or formyl-methionyl-leucyl-phenylalanine (fMLF) was unaffected. Genetic analysis of NCF4 showed compound heterozygosity for a frameshift mutation with premature stop codon and a missense mutation predicting a R105Q substitution in the PX domain. Parents and a sibling were healthy heterozygous carriers. p40(phox)R105Q lacked binding to PtdIns(3)P and failed to reconstitute phagocytosis-induced oxidase activity in p40(phox)-deficient granulocytes, with premature loss of p40(phox)R105Q from phagosomes. Thus, p40(phox) binding to PtdIns(3)P is essential for phagocytosis-induced oxidant production in human neutrophils and its absence can be associated with disease.

Granulocyte-macrophage colony-stimulating factor (GM-CSF): a chemoattractive agent for murine leukocytes in vivo.

GM‐CSF is well recognized as a proliferative agent for hematopoietic cells and exerts a priming function on neutrophils. The aim of this study was to determine if GM‐CSF has a role as a neutrophil chemoattractant in vivo and if it can contribute to recruitment during intestinal inflammation. Initial studies in vitro, using the under‐agarose gel assay, determined that GM‐CSF can induce neutrophil migration at a much lower molar concentration than the fMLP‐like peptide WKYMVm (33.5–134 nM vs. 1–10 μM). GM‐CSF‐induced neutrophil migration was ablated (<95%) using neutrophils derived from GMCSFRβ−/− mice and significantly attenuated by 42% in PI3Kγ−/−neutrophils. In vivo, a significant increase in leukocyte recruitment was observed using intravital microscopy 4 h post‐GM‐CSF (10 μg/kg) injection, which was comparable with leukocyte recruitment induced by KC (40 μg/kg). GM‐CSF‐induced recruitment was abolished, and KC‐induced recruitment was maintained in GMCSFRβ−/− mice. Furthermore, in vivo migration of extravascular leukocytes was observed toward a gel containing GM‐CSF in WT but not GMCSFRβ−/− mice. Finally, in a model of intestinal inflammation (TNBS‐induced colitis), colonic neutrophil recruitment, assessed using the MPO assay, was attenuated significantly in anti‐GM‐CSF‐treated mice or GMCSFRβ−/− mice. These data demonstrate that GM‐CSF is a potent chemoattractant in vitro and can recruit neutrophils from the microvasculature and induce extravascular migration in vivo in a β subunit‐dependent manner. This property of GM‐CSF may contribute significantly to recruitment during intestinal inflammation.

Selective Down-Regulation of Neutrophil Mac-1 in Endotoxemic Hepatic Microcirculation via IL-10

Hepatic neutrophil adhesion during endotoxemia is an integrin-independent, CD44-dependent process. Because integrins function in other endotoxemic vasculatures, we used spinning disk confocal intravital microscopy to assess whether LPS down-modulated integrin functions in sinusoids. First, we applied fMLP onto the liver surface, and compared it with systemic LPS administration. Local fMLP caused neutrophil adhesion, crawling, and emigration for at least 2 h. Surprisingly, the number of adherent and crawling neutrophils was markedly reduced in Mac-1−/− and ICAM-1−/− mice, but not in mice treated with anti-CD44 mAb. By contrast, systemic LPS injection induced a robust accumulation of neutrophils in sinusoids, which was dependent on CD44, but not on integrins. Strikingly, local fMLP could not induce any integrin-dependent adhesion in endotoxemic mice treated with anti-CD44 mAb, indicating that Mac-1-dependent neutrophil adhesion was inhibited by LPS. This response was localized to the hepatic microvasculature because neutrophils still adhered via integrins in brain microvasculature. ICAM-1/ICAM-2 levels were not decreased, but following LPS treatment, Mac-1 was down-regulated in neutrophils localized to liver, but not in the circulation. Mac-1 down-regulation in neutrophils was not observed in IL-10−/− mice. In vitro neutrophil incubation with IL-10 induced direct decrease of Mac-1 expression and adhesivity in LPS-stimulated neutrophils. Therefore, our data suggest that Mac-1 is necessary for neutrophil adhesion and crawling during local inflammatory stimuli in sinusoids, but during systemic inflammation, neutrophils are exposed to high concentrations of IL-10, leading to a CD44-dependent, integrin-independent adhesion. This may be a mechanism to keep neutrophils in sinusoids for intravascular trapping.

Infection with an intestinal helminth parasite reduces Freund's complete adjuvant-induced monoarthritis in mice.

OBJECTIVE Assessment of infection with helminth parasites in murine models of disease could identify antiinflammatory mechanisms that translate into treatments for arthritic disease. The aim of this study was to test the ability of infection with the tapeworm Hymenolepis diminuta to ameliorate Freunds complete adjuvant (CFA)-induced monoarthritis in mice. METHODS Mice received CFA with or without H diminuta, and knee swelling, pain, and measures of inflammation were assessed. RESULTS Injection of CFA resulted in rapid (within 24 hours) and sustained (lasting 20 days) knee swelling, a decreased pain threshold, increased blood flow to the knee, and increased production of tumor necrosis factor α and interleukin-12p40 (IL-12p40). In mice that were infected with H diminuta 8 days prior to receiving CFA, the severity of arthritis was reduced as assessed by these indices of inflammation and infection 2 days after CFA injection and resulted in more rapid resolution of knee swelling. This antiarthritic effect required a viable infection and was dependent on adaptive immunity, because infection with H diminuta did not protect mice lacking T cells and B cells or the IL-4 receptor α chain from CFA-induced inflammation. Interleukin-10 was of prime importance in the antiarthritic effect, because IL-10-knockout mice were not protected by infection, the antiarthritic effect was ablated by use of neutralizing IL-10 antibodies, and transfer of CD4+ cells from infected wild-type mice but not IL-10-knockout mice significantly reduced CFA-induced knee swelling. CONCLUSION In mice, the adaptive immune response to infection with H diminuta involves mobilization of IL-10, which has the concomitant advantage of dampening the innate immune responses that drive CFA-induced joint inflammation.

Divergent roles of Toll‐like receptor 2 in response to lipoteichoic acid and Staphylococcus aureus in vivo

The response of leukocytes to lipoteichoic acid (LTA), a TLR2‐dependent major cell wall component of Staphylococcus aureus, is linked to the outcome of an infection. In this study we investigated the role of nonhematopoietic TLR2 in response to LTA and S. aureus by creating bone marrow chimeras. Significant leukocyte recruitment in response to LTA required IFN‐γ priming in WT C57BL/6 and TLR2−/−⇒WT mice, but was not observed in TLR2−/− or WT⇒TLR2−/− animals. LTA also induced a proinflammatory response in IFN‐γ primed primary human microvascular endothelial cells leading to leukocyte recruitment in vitro. When mice were infected with S. aureus, the most profound elevation of TNF‐α and IL‐6 was seen in TLR2−/− and TLR2−/−⇒WT mice. TLR2−/−, but not chimeric mice, demonstrated increased IL‐17, blood leukocytosis and pulmonary neutrophilia compared to WT mice. Collectively, the results suggest an essential role for IFN‐γ and nonhematopoietic TLR2 for leukocyte recruitment in response to LTA. In contrast, TLR2 on both hematopoietic and nonhematopoietic cells appears to orchestrate an inhibitory response to S. aureus such that in complete TLR2 deficiency, there is an exaggerated proinflammatory response and/or skewing of the immune response towards a Th17 phenotype that may contribute to the decreased survival of TLR2−/− mice.

Secretory Cell Hyperplasia and Defects in Notch Activity in a Mouse Model of Leukocyte Adhesion Deficiency Type II

BACKGROUND & AIMS Leukocyte adhesion deficiency II (LAD II) is a rare condition caused by defective protein fucosylation, causing decreased leukocyte rolling, psychomotor retardation, and poor growth. The ligand-binding activity of Notch, a gastrointestinal signaling protein, depends on O-fucosylation. We investigated Notch signaling and intestinal epithelial architecture in a mouse model of LAD II. METHODS Mice lacking 3,5-epimerase/4-reductase (FX) or FX(-/-) bone marrow chimeras (with either wild-type or FX(-/-) bone marrow) were maintained on a fucose-free diet. Intestinal secretory epithelial cells were quantified by histology and immunohistochemistry. Reverse transcription-polymerase chain reaction and immunoblot analyses were used to detect Notch-regulated genes in isolated crypt epithelium. Intestinal leukocyte-endothelial interaction was quantified by intravital microscopy. The intestinal epithelium of 2-week-old FX(-/-) mice was transfected with an adenoviral vector expressing a constitutively active form of Notch. RESULTS FX(-/-) mice rapidly exhibited secretory epithelial cell hyperplasia, reduced cell proliferation, and altered epithelial gene expression patterns consistent with reduced Notch signaling. These effects were reversed when mice were given dietary fucose or by adenoviral transfection of the intestinal epithelium with the Notch intracellular domain. CONCLUSIONS In a mouse model of LAD II, secretory cell hyperplasia occurs in the small intestine and colon; these effects depend on Notch signaling. Defects in Notch signaling might therefore be involved in the pathogenesis of this rare pediatric condition.

Interactions of Enteropathogenic Escherichia coli with Pediatric and Adult Intestinal Biopsy Specimens during Early Adherence

ABSTRACT Enteropathogenic Escherichia coli (EPEC) strains cause watery diarrhea almost exclusively in young children. The basis for this age discrimination has never been determined, but it may be related to host cell receptors. During infection, EPEC strains express type IV bundle-forming pili composed of repeating subunits of the protein called bundlin. The very first interaction between EPEC and in vitro-cultured epithelial cells is mediated by the binding of α-bundlin to a carbohydrate receptor that contains, at a minimum, the N-acetyllactosamine (LacNAc) glycan sequence. However, bundlins expressed from the β-bundlin allele do not bind LacNAc glycan sequences. Herein, we investigated whether EPEC strains use α-bundlin to mediate early adherence to human intestinal biopsy specimens cultured in vitro by assessing the ability of isogenic EPEC mutants expressing either the α1- or β1-bundlin allele or a bundlin-deficient EPEC strain to bind to these specimens. Furthermore, we directly compared the abilities of a wild-type EPEC strain to bind to the epithelial surfaces of both human adult and pediatric biopsy specimens. Our results demonstrate that β-bundlin does not act as an adhesin during early EPEC adherence to adult duodenal biopsy specimens. The results also indicate that EPEC binds equally well to adult and pediatric biopsy specimens in an early adherence assay. This result is supported by the finding that the early adherence of EPEC to both adult and pediatric biopsy specimens was inhibited by LacNAc neoglycoconjugates, suggesting that organisms expressing α-bundlin-type bundle-forming pili initially bind to related glycan receptors in both age groups.

The Src kinase Fyn is protective in acute chemical‐induced colitis and promotes recovery from disease

Despite progress in understanding enteric inflammation, current therapies, although effective in many patients with inflammatory bowel disease (IBD), have significant side‐effects, and, in many patients, it is refractory to treatment. The Src kinase Fyn mediated IFN‐γ‐induced increased permeability in model epithelia, and so we hypothesized that inhibition of Fyn kinase would be anti‐colitic. Mice [B6.129SF2/J wild‐type (WT), Fyn KO, or chimeras] received 2.5% dextran sodium sulfate (DSS) or normal water for 10 d and were necropsied immediately or 3 d later. Gut permeability was assessed by FITC‐dextran flux, colitis by macroscopic and histologic parameters, and immune cell status by cytokine production and CD4+ T cell Foxp3 expression. Fyn KO mice consistently displayed significantly worse DSS‐induced disease than WT, correlating with decreased IL‐10 and increased IL‐17 in splenocytes and the gut; Fyn KO mice failed to thrive after removal of the DSS water. Analysis of chimeric mice indicated that the increased sensitivity to DSS was due to the lack of Fyn kinase in hematopoietic, but not stromal, cells, in accordance with Fyn+ T cell increases in WT mice exposed to DSS and Fyn KO mice having a reduced number of CD4+Foxp3+ cells in baseline or colitic conditions and a reduced capacity to induce Foxp3 expression in vitro. Other experiments suggest that the colonic microbiota in Fyn KO mice is not preferentially colitogenic. Contrary to our expectation, the absence of Fyn kinase resulted in greater DSS‐induced disease, and analysis of chimeric mice indicated that leukocyte Fyn kinase is beneficial in limiting colitis.

Loss of phosphoinositide 3-kinase P110γ is protective in the acute phase but detrimental in the resolution phase of hapten-induced colitis.

Background:Pharmacologic inhibition or genetic ablation of phosphoinositide 3-kinase gamma (PI3K&ggr;) has been shown to be protective against experimental colitis. However, the role of PI3K&ggr; in the resolution phase of colitis remains unexplored. In this study, we assess the effects of genetic knockout of PI3K&ggr; on the induction and resolution of colitis induced by the hapten trinitrobenzene sulfonic acid (TNBS). Methods:Colitis was induced in wild-type C57/Bl6 or PI3K&ggr;−/− mice by intrarectal administration of 2.5 mg of TNBS in 50% ethanol. Body weights were monitored daily, and colon tissues were collected at days 3, 7, or 14 after treatment, and colitis was assessed using disease activity and histologic damage scores, measurement of tissue myeloperoxidase and neutrophil infiltration, and local cytokine production. Results:Mice lacking PI3K&ggr; were significantly protected from disease during the acute phase (day 3) of TNBS colitis. However, PI3K&ggr;−/− mice have difficulty resolving acute inflammation because they failed to restore lost weight and had significantly elevated histologic damage scores and tissue myeloperoxidase levels at days 7 and 14 after TNBS administration compared with wild-type controls. This phenomenon was dependent on presensitization with TNBS and seems to involve an inability to clear invading bacteria, resulting in the generation of a persistent inflammatory cytokine response. Conclusions:This study confirms that PI3K&ggr; plays a role in the induction of colitis. However, PI3K&ggr; is also required for the resolution of intestinal damage following acute inflammation. This must be taken into consideration before the inhibition of PI3K&ggr; can be used as a treatment for disorders such as inflammatory bowel disease.