IL-10 differentially controls the infiltration of inflammatory macrophages and antigen-presenting cells during inflammation

The inflammatory activation and recruitment of defined myeloid populations is essential for controlling the bridge between innate and adaptive immunity and shaping the immune response to microbial challenge. However, these cells exhibit significant functional heterogeneity and the inflammatory signals that differentially influence their effector characteristics are poorly characterized. In this study, we defined the phenotype of discrete subsets of effective antigen-presenting cells (APCs) in the peritoneal cavity during peritonitis. When the functional properties of these cells were compared to inflammatory monocyte-derived macrophages we noted differential responses to the immune-modulatory cytokine IL-10. In contrast to the suppressive actions of IL-10 on inflammatory macrophages, the recruitment of APCs was relatively refractory and we found no evidence for selective inhibition of APC differentiation. This differential response of myeloid cell subsets to IL-10 may thus have limited impact on development of potentially tissue-damaging adaptive immune responses, whilst restricting the magnitude of the inflammatory response. These findings may have clinical relevance in the context of peritoneal dialysis patients, where recurrent infections are associated with immune-mediated membrane dysfunction, treatment failure and increased morbidity

Human neutrophil clearance of bacterial pathogens triggers anti-microbial gamma delta T cell responses in early infection

Human blood Vc9/Vd2 T cells, monocytes and neutrophils share a responsiveness toward inflammatory chemokines and are rapidly recruited to sites of infection. Studying their interaction in vitro and relating these findings to in vivo observations in patients may therefore provide crucial insight into inflammatory events. Our present data demonstrate that Vc9/Vd2 T cells provide potent survival signals resulting in neutrophil activation and the release of the neutrophil chemoattractant CXCL8 (IL-8). In turn, Vc9/Vd2 T cells readily respond to neutrophils harboring phagocytosed bacteria, as evidenced by expression of CD69, interferon (IFN)-c and tumor necrosis factor (TNF)-a. This response is dependent on the ability of these bacteria to produce the microbial metabolite (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMB-PP), requires cell-cell contact of Vc9/Vd2 T cells with accessory monocytes through lymphocyte function-associated antigen-1 (LFA-1), and results in a TNF-a dependent proliferation of Vc9/Vd2 T cells. The antibiotic fosmidomycin, which targets the HMB-PP biosynthesis pathway, not only has a direct antibacterial effect on most HMB-PP producing bacteria but also possesses rapid anti-inflammatory properties by inhibiting cd T cell responses in vitro. Patients with acute peritoneal-dialysis (PD)-associated bacterial peritonitis – characterized by an excessive influx of neutrophils and monocytes into the peritoneal cavity – show a selective activation of local Vc9/Vd2 T cells by HMB-PP producing but not by HMB-PP deficient bacterial pathogens. The cd T celldriven perpetuation of inflammatory responses during acute peritonitis is associated with elevated peritoneal levels of cd T cells and TNF-a and detrimental clinical outcomes in infections caused by HMB-PP positive microorganisms. Taken together, our findings indicate a direct link between invading pathogens, neutrophils, monocytes and microbe-responsive cd T cells in early infection and suggest novel diagnostic and therapeutic approaches.Martin S. Davey, Chan-Yu Lin, Gareth W. Roberts, Sinéad Heuston, Amanda C. Brown, James A. Chess, Mark A. Toleman, Cormac G.M. Gahan, Colin Hill, Tanya Parish, John D. Williams, Simon J. Davies, David W. Johnson, Nicholas Topley, Bernhard Moser and Matthias Eber

Unconventional human T cells accumulate at the site of infection in response to microbial ligands and induce local tissue remodeling

The antimicrobial responsiveness and function of unconventional human T cells are poorly understood, with only limited access to relevant specimens from sites of infection. Peritonitis is a common and serious complication in individuals with end-stage kidney disease receiving peritoneal dialysis. By analyzing local and systemic immune responses in peritoneal dialysis patients presenting with acute bacterial peritonitis and monitoring individuals before and during defined infectious episodes, our data show that Vg9/ Vd2+ gd T cells and mucosal-associated invariant T cells accumulate at the site of infection with organisms producing (E)-4- hydroxy-3-methyl-but-2-enyl pyrophosphate and vitamin B2, respectively. Such unconventional human T cells are major producers of IFN-g and TNF-a in response to these ligands that are shared by many microbial pathogens and affect the cells lining the peritoneal cavity by triggering local inflammation and inducing tissue remodeling with consequences for peritoneal membrane integrity. Our data uncover a crucial role for Vg9/Vd2 T cells and mucosal-associated invariant T cells in bacterial infection and suggest that they represent a useful predictive marker for important clinical outcomes, which may inform future stratification and patient management. These findings are likely to be applicable to other acute infections where local activation of unconventional T cells contributes to the antimicrobial inflammatory response

Barriers and facilitators to physical activity: a comparative analysis of transplant athletes competing in high intensity sporting events with other transplant recipients

Background: There is widespread recognition that many transplant recipients struggle to become and remain physically active. However, some transplant recipients do undertake strenuous training and significant physical activity (PA) and participate in intensive sports.Aim: This study sought to understand facilitators and barriers to be physically active for Transplant Athletes (TXA) compared to a group of Dutch transplantees. This explorative mixed methods study analysed race performance and interview data from TxA who participated in cycling and/or the sprint triathlon at the World Transplant Games 2023, and compared their lived experiences in terms of barriers and facilitators of PA with those of 16 transplantees in a study from the Netherlands previously published in this journal.Methods: Using Patient and Public Involvement and engagement (PPI), race data from World Transplant Games 2023 and subsequent in-depth interviews were used from 27 TxA. A visual artefact of barriers and facilitators from the previous Dutch study was used to prompt identification and discussion of barriers and facilitators of PA. Interview data were coded by three coders.Results: Many of the barriers to PA previously reported by Dutch transplant recipients were not shared by the majority of TxA in this study. The TxA in this study reported significantly lower physical limitations, lower fear to undertake exercise, and no comorbidity issues for TxA. Furthermore, TxA perceived they received substantial social support, had the strength to do PA, and were in control of their weight.Conclusion: Several TxA reported a lack of understanding from medical and other professionals about the appropriate intensity of PA. An evidence-based framework of PA for transplant recipients and transplant athletes is needed for safe and appropriate PA

Peritoneal macrophage heterogeneity is associated with different peritoneal dialysis outcomes

Peritonitis remains the major obstacle for the maintenance of long-term peritoneal dialysis and dysregulated host peritoneal immune responses may compromise local anti-infectious defense, leading to treatment failure. Whilst, tissue mononuclear phagocytes, comprising macrophages and dendritic cells, are central to a host response to pathogens and the development of adaptive immune responses, they are poorly characterized in the human peritoneum. Combining flow cytometry with global transcriptome analysis, the phenotypic features and lineage identity of the major CD14+ macrophage and CD1c+ dendritic cell subsets in dialysis effluent were defined. Their functional specialization was reflected in cytokine generation, phagocytosis, and antigen processing/presentation. By analyzing acute bacterial peritonitis, stable (infection-free) and new-starter patients receiving peritoneal dialysis, we identified a skewed distribution of macrophage to dendritic cell subsets (increasing ratio) that associated with adverse peritonitis outcomes, history of multiple peritonitis episodes, and early catheter failure, respectively. Intriguingly, we also noted significant alterations of macrophage heterogeneity, indicative of different maturation and activation states that were associated with different peritoneal dialysis outcomes. Thus, our studies delineate peritoneal dendritic cells from macrophages within dialysate, and define cellular characteristics associated with peritoneal dialysis treatment failure. These are the first steps to unravelling the detrimental adaptive immune responses occurring as a consequence of peritonitis

Interferon-γ inhibits interleukin-1β-induced matrix metalloproteinase production by synovial fibroblasts and protects articular cartilage in early arthritis

Introduction: The first few months after symptom onset represents a pathologically distinct phase in rheumatoid arthritis (RA). We used relevant experimental models to define the pathological role of interferon-γ (IFN-γ) during early inflammatory arthritis. Methods: We studied IFN-γ's capacity to modulate interleukin-1β (IL-1β) induced degenerative responses using RA fibroblast-like synoviocytes (FLS), a bovine articular cartilage explant (BACE)/RA-FLS co-culture model and an experimental inflammatory arthritis model (murine antigen-induced arthritis (AIA)). Results: IFN-γ modulated IL-1β driven matrix metalloproteinases (MMP) synthesis resulting in the down-regulation of MMP-1 and MMP-3 production in vitro. IFN-γ did not affect IL-1β induced tissue inhibitor of metalloproteinase-1 (TIMP-1) production by RA FLS but skewed the MMP/TIMP-1 balance sufficiently to attenuate glycosaminoglycan-depletion in our BACE model. IFN-γ reduced IL-1β expression in the arthritic joint and prevented cartilage degeneration on Day 3 of AIA. Conclusions: Early therapeutic intervention with IFN-γ may be critical to orchestrate tissue-protective responses during inflammatory arthritis

Human peritoneal mesothelial cells respond to bacterial ligands through a specific subset of Toll-like receptors

Background. Bacterial infection remains a major cause of morbidity and mortality in peritoneal dialysis (PD) patients worldwide. Previous studies have identified a key role for mesothelial cells, lining the peritoneal cavity, in coordinating inflammation and host defense. Toll-like receptor (TLR) involvement in early activation events within the mesothelium, however, remains poorly defined. To investigate the initiation of bacterial peritonitis, we characterized TLR activation by bacterial ligands in human peritoneal mesothelial cells (HPMC)

Type-1 fimbriate escherichia-coli stimulates a unique pattern of de-granulation by human polymorphonuclear leukocytes

Uropathogenic strains of Escherichia coli bearing mannose-sensitive (type 1) fimbriae promote a unique pattern of degranulation from human polymorphonuclear leukocytes (PMN). Significant quantities of the primary (1 degree) and tertiary (3 degree) granule markers, neutral protease-myeloperoxidase and N-acetyl-beta-D-glucosaminidase, respectively, were released by PMN in a dose- and time-dependent manner when stimulated by these defined bacterial strains. Organisms bearing mannose-resistant (P) fimbriae promoted release of only the secondary (2 degree) granule marker, vitamin B12-binding protein. When this pattern of degranulation was compared to that produced by PMN in response to a variety of soluble and particulate stimuli, only the calcium ionophore A23187 similarly triggered 1 degree and 3 degree granule marker release. All the other stimuli tested--zymosan, serum-treated and unopsonized; n-formylmethionyl-leucyl-phenylalanine; and phorbol myristate acetate--promoted release of only the 2 degree granule marker. These results demonstrate selectivity of PMN degranulation in response to a number of transmembrane signals. In addition, the capacity of E. coli to promote PMN degranulation is dependent on its phenotypic fimbrial expression, a surface characteristic which correlates significantly with its relative surface hydrophobicity as measured by binding to octyl Sepharose. Those bacteria demonstrating the greatest hydrophobicity were capable of triggering discharge of all three granule marker proteins. Thus, the mannose-sensitive fimbriae of uropathogenic E. coli may contribute significantly to their potential pathophysiologic role in renal scarring

Peritonitis in Peritoneal Dialysis patients: the case for rapid diagnosis, targeted treatment and monitoring to improve outcomes

Peritoneal dialysis (PD) is a cost-effective, home-based treatment option for patients with end-stage renal disease; however, PD is declining in many countries. A major reason for this is peritonitis, which commonly leads to technique failure and has led to negative perceptions of PD by clinicians and patients. To restore confidence in PD, better diagnostics are required to enable appropriate treatment to be started earlier; this needs to be coupled with improved understanding of the biology of peritonitis. Advances in culture-independent microbiological methods, in particular the use of bacterial flow cytometry and immune fingerprinting techniques, can enable organism detection and antimicrobial susceptibility testing to be performed in as little as 3 hours after samples are received. At the same time, improved understanding of peritoneal mesothelial cell responses to infection is providing insights into pathways that may be targeted to dampen deleterious elementsof the host immune response, promote healing, and preserve membrane function