CX3CR1 defines functionally distinct intestinal mononuclear phagocyte subsets which maintain their respective functions during homeostatic and inflammatory conditions

Intestinal mononuclear phagocytes (iMNP) are critically involved in mucosal immunity and tissue homeostasis. Two major non-overlapping populations of iMNP have been identified in mice. CD103(+) iMNP represent a migratory population capable of inducing tolerogenic responses, whereas CX3CR1(+) iMNP are resident cells with disease-promoting potential. CX3CR1(+) iMNP can further be subdivided based on differential expression of CX3CR1. Using CX3CR1(GFP/+) ×RAG2(-/-) mice, we demonstrate that CX3CR1(hi) and CX3CR1(lo) iMNP clearly differ with respect to their morphological and functional properties. Compared with CX3CR1(hi) iMNP, CX3CR1(lo) iMNP are polarised towards pro-inflammatory responses already under homeostatic conditions. During a CD4(+) T-cell-induced colitis, CX3CR1(lo) cells accumulate in the inflamed mucosa and upregulate the expression of pro-inflammatory cytokines and triggering receptor expressed on myeloid cells-1 (TREM-1). In contrast, CX3CR1(hi) iMNP retain their non-inflammatory profile even during intestinal inflammation. These findings identify two functionally distinct iMNP subsets based on differential expression of CX3CR1 and indicate an unanticipated stability of iMNP

The liver may act as a firewall mediating mutualism between the host and its gut commensal microbiota.

A prerequisite for establishment of mutualism between the host and the microbial community that inhabits the large intestine is the stringent mucosal compartmentalization of microorganisms. Microbe-loaded dendritic cells trafficking through lymphatics are arrested at the mesenteric lymph nodes, which constitute the firewall of the intestinal lymphatic circulation. We show in different mouse models that the liver, which receives the intestinal venous blood circulation, forms a vascular firewall that captures gut commensal bacteria entering the bloodstream during intestinal pathology. Phagocytic Kupffer cells in the liver of mice clear commensals from the systemic vasculature independently of the spleen through the liver's own arterial supply. Damage to the liver firewall in mice impairs functional clearance of commensals from blood, despite heightened innate immunity, resulting in spontaneous priming of nonmucosal immune responses through increased systemic exposure to gut commensals. Systemic immune responses consistent with increased extraintestinal commensal exposure were found in humans with liver disease (nonalcoholic steatohepatitis). The liver may act as a functional vascular firewall that clears commensals that have penetrated either intestinal or systemic vascular circuits

TREM-1 deficiency can attenuate disease severity without affecting pathogen clearance.

Triggering receptor expressed on myeloid cells-1 (TREM-1) is a potent amplifier of pro-inflammatory innate immune reactions. While TREM-1-amplified responses likely aid an improved detection and elimination of pathogens, excessive production of cytokines and oxygen radicals can also severely harm the host. Studies addressing the pathogenic role of TREM-1 during endotoxin-induced shock or microbial sepsis have so far mostly relied on the administration of TREM-1 fusion proteins or peptides representing part of the extracellular domain of TREM-1. However, binding of these agents to the yet unidentified TREM-1 ligand could also impact signaling through alternative receptors. More importantly, controversial results have been obtained regarding the requirement of TREM-1 for microbial control. To unambiguously investigate the role of TREM-1 in homeostasis and disease, we have generated mice deficient in Trem1. Trem1(-/-) mice are viable, fertile and show no altered hematopoietic compartment. In CD4(+) T cell- and dextran sodium sulfate-induced models of colitis, Trem1(-/-) mice displayed significantly attenuated disease that was associated with reduced inflammatory infiltrates and diminished expression of pro-inflammatory cytokines. Trem1(-/-) mice also exhibited reduced neutrophilic infiltration and decreased lesion size upon infection with Leishmania major. Furthermore, reduced morbidity was observed for influenza virus-infected Trem1(-/-) mice. Importantly, while immune-associated pathologies were significantly reduced, Trem1(-/-) mice were equally capable of controlling infections with L. major, influenza virus, but also Legionella pneumophila as Trem1(+/+) controls. Our results not only demonstrate an unanticipated pathogenic impact of TREM-1 during a viral and parasitic infection, but also indicate that therapeutic blocking of TREM-1 in distinct inflammatory disorders holds considerable promise by blunting excessive inflammation while preserving the capacity for microbial control

Prävention, Diagnostik, Therapie und Nachsorge des Lungenkarzinoms: Interdisziplinäre S3-Leitlinie der Deutschen Gesellschaft für Pneumologie und Beatmungsmedizin und der Deutschen Krebsgesellschaft – Kurzfassung

Die aktuelle Fassung der Leitlinie Lungenkarzinom trägt der Dynamik der Informationen in diesem Fachbereich Rechnung. Insbesondere gelten folgenden Empfehlungen: Die Vorstellung aller neu diagnostizierten Patienten im interdisziplinären pneumoonkologischen Tumorboard ist verpflichtend, das CT-Screening für asymptomatische Risikopersonen (nach Zulassung durch die Behörden), Vorgehen beim inzidentellen Lungenrundherd (außerhalb von Screeningprogrammen), molekulare Testung aller NSCLC unabhängig vom Subtyp, in frühen Stadien auf EGFR-Mutationen und in der Rezidivsituation, adjuvante TKI-Therapie bei Vorliegen einer EGFR-Mutation, adjuvante Konsolidierung mit Checkpointinhibitor bei PD-L1 ≥ 50%, Erhebung des PD-L1-Status, nach Radiochemotherapie bei PD-L1-pos. Tumoren Konsolidierung mit Checkpointinhibitor, adjuvante Konsolidierung mit Checkpointinhibitor bei PD-L1 ≥ 50% im Stadium IIIA, Erweiterung des therapeutischen Spektrums bei PD-L1 ≥ 50%, unabhängig von PD-L1Status, neue zielgerichtete Therapieoptionen sowie die Einführung der Immunchemotherapie in der SCLC Erstlinie. Um eine zeitnahe Umsetzung künftiger Neuerungen zu gewährleisten, wurde die Umstellung auf eine „living guideline“ für das Lungenkarzinom befürwortet. // The current S3 Lung Cancer Guidelines are edited with fundamental changes to the previous edition based on the dynamic influx of information to this field:The recommendations include de novo a mandatory case presentation for all patients with lung cancer in a multidisciplinary tumor board before initiation of treatment, furthermore CT-Screening for asymptomatic patients at risk (after federal approval), recommendations for incidental lung nodule management , molecular testing of all NSCLC independent of subtypes, EGFR-mutations in resectable early stage lung cancer in relapsed or recurrent disease, adjuvant TKI-therapy in the presence of common EGFR-mutations, adjuvant consolidation treatment with checkpoint inhibitors in resected lung cancer with PD-L1 ≥ 50%, obligatory evaluation of PD-L1-status, consolidation treatment with checkpoint inhibition after radiochemotherapy in patients with PD-L1-pos. tumor, adjuvant consolidation treatment with checkpoint inhibition in patients withPD-L1 ≥ 50% stage IIIA and treatment options in PD-L1 ≥ 50% tumors independent of PD-L1status and targeted therapy and treatment option immune chemotherapy in first line SCLC patients.Based on the current dynamic status of information in this field and the turnaround time required to implement new options, a transformation to a "living guideline" was proposed

Upon colitis induction, <i>Trem1^−/− x Rag2^−/−</i> mice exhibit substantially reduced inflammatory infiltrates and diminished expression of pro-inflammatory mediators.

<p>(A–C) Lamina propria cells were isolated from the colon of <i>Trem1^+/+ x Rag2^−/−</i> and <i>Trem1^−/− x Rag2^−/−</i> mice 12–13 days post adoptive transfer of colitogenic CD4 T cells or from untransferred mice (healthy colons) and analysed by FACS. (A) After exclusion of doublets and dead cells, CD11b⁺ cells were discriminated from CD4⁺ T cells and further subgated into MHCII^lo Gr1⁺ (gate 1) and MHCII^hi Gr1⁻ (gate 2) cells. In gate 1, monocytes and neutrophils were identified according to their Ly6C^hi Gr1^int and Ly6C^int Gr1^hi phenotype, respectively. In gate 2, MHCII⁺ cells were further subdivided into two populations of MHCII^int Ly6C^hi and MHCII^hi Ly6C^lo cells. (B, C) Absolute numbers of total cells recovered from individual mice (symbols; lines indicate mean values per group) and mean values ± SEM for CD45⁺ cells, CD4⁺ T cells, CD11b⁺ cells and subsets defined within the CD11b⁺ gate as illustrated in (A). Per group, n = 9 mice adoptively transferred with CD4 T cells (B) and n = 4 untransferred (C) mice were analysed. (D) TREM-1 surface expression by neutrophils (Ly6C^int Gr1^hi), monocytes (Ly6C^hi Gr1^int) and CD11b⁺ Gr1⁻ Ly6C⁺ versus Ly6C⁻ subsets identified in the lamina propria (according to the gating strategy depicted in D) of colitic (n = 9) versus healthy (n = 4) <i>Trem1^+/+ x Rag2^−/−</i> mice. (E) Colonic tissues were assessed for the expression of pro-inflammatory mediators by qRT-PCR. Bars show mean values ± SEM for n = 9 mice. ***, p<0.001; **, p<0.01; *, p<0.05. N.D. = not determined due to insufficient cell numbers.</p

<i>Trem1^−/−</i> mice are equally capable of clearing <i>L. pneumophila</i> as <i>Trem1^+/+</i> controls.

<p><i>Trem1^+/+</i> and <i>Trem1^−/−</i> mice were infected intranasally with 5×10⁶ CFU <i>L. pneumophila</i>. 3 days post infection CFU (A) and neutrophils (B) were quantified in the BALF. ns, no statistically significant difference. Pooled data from two independent experiments are shown.</p

<i>Trem1^−/− x Rag2^−/−</i> mice are protected from a CD4⁺ T cell-induced colitis.

<p>Colitis was induced in <i>Trem1^+/+ x Rag2^−/−</i> (filled circles) and <i>Trem1^−/− x Rag2^−/−</i> mice (white circles) by i.p. injection of 2×10⁵ CD4⁺ CD45RB^hi T cells. (A) Weight loss relative to the initial body weight. Mean values of n = 9 mice analysed per group are shown with error bars indicating the SEM. (B) Colon lengths were determined in individual mice (symbols). Lines show mean values for each group of mice. (C) Representative H&E-stained colonic tissue sections of a <i>Trem1^+/+ x Rag2^−/−</i> (histopathological score: 14) and <i>Trem1^−/− x Rag2^−/−</i> mouse (histopathological score: 2). (D) Total histopathological scores. Symbols show total scores for individual mice and lines indicate the mean value for each group of mice. Histopathological scores were determined for individual mice by a pathologist according to parameters defined in the <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003900#s4" target="_blank">Materials and Methods</a> section. (E) Individual parameters of histopathological scoring. Columns show mean values for n = 9 mice analysed per group and error bars indicate the SEM. ****, p<0.0001; ***, p<0.001; **, p<0.01. One representative experiment out of three independent experiments is shown.</p

Unimpaired hematopoiesis in <i>Trem1^−/−</i> mice.

<p>(A) Representative dot plots show the FACS-based identification of lineage-depleted (lin⁻) Sca1⁺ c-kit^hi (LSK) cells and lin⁻ Sca1⁻ c-Kit^hi myeloid progenitors in <i>Trem1^+/+</i> (top panels) and <i>Trem1^−/−</i> (bottom panels) bone marrow (BM) following lineage depletion and depletion of lymphoid progenitors by MACS. Common myeloid progenitors (CMP), granulocyte-macrophage progenitors (GMP) and megakaryocyte/erythrocyte progenitors (MEP) were further discriminated according to their expression of FcγR and CD34. Filled histograms show TREM-1 surface expression by LSK cells, CMP, GMP and MEP progenitors from <i>Trem1^−/−</i> mice in comparison to <i>Trem1^+/+</i> mice (lines). (B) Absolute cell numbers of total BM cells, lin⁻ BM cells, lin⁻ Sca1⁻ c-kit^hi myeloid progenitors, LSK cells, CMP, GMP and MEP and colony forming units (CFU) of hematopoietic precursors isolated from the BM of <i>Trem1^+/+</i> and <i>Trem1^−/−</i> mice were determined as described in the <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003900#s4" target="_blank">Materials and Methods</a> section. Mean values of n = 2 mice analysed are shown with error bars indicating the range. (C) Mixed BM chimeras were generated by i.v. transfer of 1∶1 mixed <i>Trem1^+/+ x GFP^+/+</i> and <i>Trem1^−/− x GFP^−/−</i> BM cells (white circles, dotted lines) into irradiated recipient mice. As control, and to account for potential interfering effects of the GFP expression, mixed BM from <i>Trem1^+/+ x GFP^+/+</i> and <i>Trem1^+/+ x GFP^−/−</i> mice (black circles and lines) was transferred into additional recipient mice. BM chimeras were analyzed after 10 and 31 weeks of chimerism. Neutrophils, Ly6C^hi and Ly6C^lo monocytes were identified in the peripheral blood according to the depicted gating strategy and the GFP⁻ : GFP⁺ cell ratio in the respective cell subsets was determined. Mean values of n = 4–5 mice analyzed per group are shown with error bars indicating the SEM. ns, no statistically significant difference. Data depicted in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003900#ppat-1003900-g002" target="_blank">Figure 2</a> are representative of two independent experiments.</p