Tacrolimus Impairs Kupffer Cell Capacity to Control Bacteremia: Why Transplant Recipients Are Susceptible to Infection

Kupffer cell reverse migration into the liver sinusoids mitigates neonatal sepsis and meningitis

In adults, liver-resident macrophages, or Kupffer cells (KCs), reside in the sinusoids and sterilize circulating blood by capturing rapidly flowing microbes. We developed quantitative intravital imaging of 1-day-old mice combined with transcriptomics, genetic manipulation, and in vivo infection assays to interrogate increased susceptibility of newborns to bloodstream infections. Whereas 1-day-old KCs were better at catching Escherichia coli in vitro, we uncovered a critical 1-week window postpartum when KCs have limited access to blood and must translocate from liver parenchyma into the sinusoids. KC migration was independent of the microbiome but depended on macrophage migration inhibitory factor, its receptor CD74, and the adhesion molecule CD44. On the basis of our findings, we propose a model of progenitor macrophage seeding of the liver sinusoids via a reverse transmigration process from liver parenchyma. These results also illustrate the importance of developing newborn mouse models to understand newborn immunity and disease.

Infective endocarditis with metastatic infections in a renal transplant recipient: a case report

BACKGROUND

Infective endocarditis is an uncommon but well-known post-transplant complication with significant morbidity and mortality. It has been observed to be about 171 times more common in solid organ transplant patients than in the general population. With the increasing rate of end-stage kidney disease, the higher demand for kidney transplantation with better graft survival, and life expectancy rates, more transplant recipients may develop infective endocarditis as a late post-transplant complication. Prompt diagnosis of infective endocarditis is therefore necessary to avert graft loss and other life-threatening outcomes.

CASE PRESENTATION

We present a case of a 52-year-old African patient who had a live donor kidney transplant 18 months prior to presentation and had been on oral tacrolimus 5 mg every morning/4.5 mg every evening, mycophenolic acid (MPA) 720 mg twice daily, and oral prednisolone 10 mg daily as maintenance immunosuppressive medications. Regarding the above immunosuppressive medications, he had been in good health and had a functioning transplant graft. He presented with a resolving right thigh swelling, recurrence of fever, new onset left hemiplegia, and seizures. Enterococcus faecalis infective endocarditis was diagnosed with metastatic brain abscesses, which was treated with intravenous vancomycin and gentamycin for 5 weeks. There are very few reported cases of infective endocarditis due to Enterococcus faecalis, and this case is unique because the initial presentation was pyomyositis.

CONCLUSION

Infective endocarditis with septic embolization to the brain should be considered in kidney transplant recipients with pyomyositis and multiple rim-enhancing lesions, especially in the late post-transplant period with Enterococcal spp. as an emerging cause of infective endocarditis in kidney transplant recipients. Clinicians will need to have a high index of suspicion to aid early diagnosis with appropriate treatment to prevent adverse outcomes.

Efficacy and safety of calcineurin inhibitors (CNIs) for septic patients in ICU: a cohort study from MIMIC database

Background

Sepsis is marked by a dysregulated immune response to infection. Calcineurin inhibitors (CNIs), commonly used as immunosuppressants, have unique properties that may help mitigate the overactive immune response in sepsis, potentially leading to better patient outcomes. This study aims to assess whether CNIs improve prognosis in septic patients and to evaluate any associated adverse reactions.

Methods

We utilized the Medical Information Mart for Intensive Care IV 2.2 (MIMIC-IV 2.2) database to identify septic patients who were treated with CNIs and those who were not. Propensity score matching (PSM) was employed to balance baseline characteristics between the CNI user group and the non-user group. The primary outcome was 28-day mortality, analyzed using the Kaplan-Meier method and Cox proportional hazard regression models to examine the relationship between CNI use and patient survival.

Results

From the MIMIC-IV database, 22,517 septic patients were identified. After propensity score matching, a sample of 874 patients was analyzed. The CNI group exhibited a significantly lower 28-day mortality risk compared to the non-user group (HR: 0.26; 95% CI: 0.17, 0.41) in the univariate Cox hazard analysis. Kaplan-Meier survival curves also demonstrated a significantly higher 28- and 365-day survival rate for CNI users compared to non-users (log-rank test p-value = 0.001). No significant association was found between CNI use and an increased risk of new-onset infection (p = 0.144), but an association with mild hypertension (P < 0.001) and liver injury (P < 0.001) was observed.

Conclusion

The use of calcineurin inhibitors was associated with reduced short- and long-term mortality in septic patients without an increased incidence of new-onset infections, hyperkalemia, severe hypertension, or acute kidney injury (AKI). However, CNI use may lead to adverse effects, such as liver injury and mild hypertension.

Role of the immune system in liver transplantation and its implications for therapeutic interventions

Liver transplantation (LT) stands as the gold standard for treating end-stage liver disease and hepatocellular carcinoma, yet postoperative complications continue to impact survival rates. The liver's unique immune system, governed by a microenvironment of diverse immune cells, is disrupted during processes like ischemia-reperfusion injury posttransplantation, leading to immune imbalance, inflammation, and subsequent complications. In the posttransplantation period, immune cells within the liver collaboratively foster a tolerant environment, crucial for immune tolerance and liver regeneration. While clinical trials exploring cell therapy for LT complications exist, a comprehensive summary is lacking. This review provides an insight into the intricacies of the liver's immune microenvironment, with a specific focus on macrophages and T cells as primary immune players. Delving into the immunological dynamics at different stages of LT, we explore the disruptions after LT and subsequent immune responses. Focusing on immune cell targeting for treating liver transplant complications, we provide a comprehensive summary of ongoing clinical trials in this domain, especially cell therapies. Furthermore, we offer innovative treatment strategies that leverage the opportunities and prospects identified in the therapeutic landscape. This review seeks to advance our understanding of LT immunology and steer the development of precise therapies for postoperative complications.

Kupffer cell-like syncytia replenish resident macrophage function in the fibrotic liver

Kupffer cells (KCs) are localized in liver sinusoids but extend pseudopods to parenchymal cells to maintain their identity and serve as the body's central bacterial filter. Liver cirrhosis drastically alters vascular architecture, but how KCs adapt is unclear. We used a mouse model of liver fibrosis and human tissue to examine immune adaptation. Fibrosis forced KCs to lose contact with parenchymal cells, down-regulating "KC identity," which rendered them incapable of clearing bacteria. Commensals stimulated the recruitment of monocytes through CD44 to a spatially distinct vascular compartment. There, recruited monocytes formed large aggregates of multinucleated cells (syncytia) that expressed phenotypical KC markers and displayed enhanced bacterial capture ability. Syncytia formed via CD36 and were observed in human cirrhosis as a possible antimicrobial defense that evolved with fibrosis.

Ontogeny, functions and reprogramming of Kupffer cells upon infectious disease

The liver is a vital metabolic organ that also performs important immune-regulatory functions. In the context of infections, the liver represents a target site for various pathogens, while also having an outstanding capacity to filter the blood from pathogens and to contain infections. Pathogen scavenging by the liver is primarily performed by its large and heterogeneous macrophage population. The major liver-resident macrophage population is located within the hepatic microcirculation and is known as Kupffer cells (KCs). Although other minor macrophages reside in the liver as well, KCs remain the best characterized and are the best well-known hepatic macrophage population to be functionally involved in the clearance of infections. The response of KCs to pathogenic insults often governs the overall severity and outcome of infections on the host. Moreover, infections also impart long-lasting, and rarely studied changes to the KC pool. In this review, we discuss current knowledge on the biology and the various roles of liver macrophages during infections. In addition, we reflect on the potential of infection history to imprint long-lasting effects on macrophages, in particular liver macrophages.

Breaking the Gingival Barrier in Periodontitis

The break of the epithelial barrier of gingiva has been a subject of minor interest, albeit playing a key role in periodontal pathology, transitory bacteraemia, and subsequent systemic low-grade inflammation (LGI). The significance of mechanically induced bacterial translocation in gingiva (e.g., via mastication and teeth brushing) has been disregarded despite the accumulated knowledge of mechanical force effects on tight junctions (TJs) and subsequent pathology in other epithelial tissues. Transitory bacteraemia is observed as a rule in gingival inflammation, but is rarely observed in clinically healthy gingiva. This implies that TJs of inflamed gingiva deteriorate, e.g., via a surplus of lipopolysaccharide (LPS), bacterial proteases, toxins, Oncostatin M (OSM), and neutrophil proteases. The inflammation-deteriorated gingival TJs rupture when exposed to physiological mechanical forces. This rupture is characterised by bacteraemia during and briefly after mastication and teeth brushing, i.e., it appears to be a dynamic process of short duration, endowed with quick repair mechanisms. In this review, we consider the bacterial, immune, and mechanical factors responsible for the increased permeability and break of the epithelial barrier of inflamed gingiva and the subsequent translocation of both viable bacteria and bacterial LPS during physiological mechanical forces, such as mastication and teeth brushing.

Crosstalk between liver macrophages and gut microbiota: An important component of inflammation-associated liver diseases

Hepatic macrophages have been recognized as primary sensors and responders in liver inflammation. By processing host or exogenous biochemical signals, including microbial components and metabolites, through the gut-liver axis, hepatic macrophages can both trigger or regulate inflammatory responses. Crosstalk between hepatic macrophages and gut microbiota is an important component of liver inflammation and related liver diseases, such as acute liver injury (ALI), alcoholic liver disease (ALD), and nonalcoholic fatty liver disease (NAFLD). This review summarizes recent advances in knowledge related to the crosstalk between hepatic macrophages and gut microbiota, including the therapeutic potential of targeting hepatic macrophages as a component of gut microecology in inflammation-associated liver diseases.

Machine perfusion combined with antibiotics prevents donor-derived infections caused by multidrug-resistant bacteria

Donor infection affects organ utilization, especially the infections by multidrug-resistant bacteria, which may have disastrous outcomes. We established a rat model, inoculated with Escherichia coli or carbapenem-resistant Klebsiella pneumoniae (CRKP), to investigate whether hypothermic machine perfusion (HMP), normothermic machine perfusion (NMP), or static cold storage (SCS) combined with antibiotic (AB) could eliminate the bacteria. E. coli or CRKP-infected kidneys were treated with cefoperazone-sulbactam and tigecycline, respectively. The HMP+AB and NMP+AB treatments had significant therapeutic effects on E. coli or CRKP infection compared with the SCS+AB treatment. The bacterial load of CRKP-infected kidneys in the HMP+AB (22 050 ± 2884 CFU/g vs. 1900 ± 400 CFU/g, p = .007) and NMP+AB groups (25 433 ± 2059 CFU/g vs. 500 ± 458 CFU/g, p = .002) were significantly reduced, with no statistically significant difference between both groups. Subsequently, the CRKP-infected kidneys of the HMP+AB and SCS+AB groups were transplanted. The rats in the SCS+AB group were severe infected and euthanized on day 4 post-transplant. By contrast, the rats in the HMP+AB group were in good condition. In conclusion, HMP and NMP combined with AB seems to be efficient approaches to decrease bacterial load of infected kidneys. This might lead to higher utilization rates of donors with active infection.

Does immunosuppression use increase perioperative wound morbidity in patients undergoing transversus abdominis release?

BACKGROUND

Transversus abdominis release is an effective procedure for complex ventral hernias. As wound complications contribute to hernia recurrences, mitigating risk factors is vitally important for hernia surgeons. Although immunosuppression can impair wound healing, it has inconsistently predicted wound occurrences, and its effect on wound morbidity after a transversus abdominis release is unknown.

METHODS

Patients undergoing either an elective open or robotic bilateral transversus abdominis release with permanent synthetic mesh were retrospectively stratified by perioperative immunosuppression and secondarily by procedure type (open versus robotic) and immunosuppression.

RESULTS

A total of 321 patients were included for analysis. Overall, 63 (19.6%) patients were on chronic immunosuppression, with history of solid-organ transplant being the most common indication (43 patients). Patients stratified by perioperative immunosuppression were well-matched with similar defect size (P = .97), body mass index ≥30 (P = .32), diabetes (P = .09), history of surgical site infection (P = .53), surgical approach (P = .53), and tobacco use history (P = .33). No differences between cohorts were elicited for any wound event when stratified by immunosuppression use. Similarly, no differences were elicited when cohorts were further stratified also by procedure type.

CONCLUSION

Chronic immunosuppression is often viewed as a notable risk factor for wound occurrences after surgery. However, our data suggest immunosuppression may not significantly increase the risk of perioperative wound morbidity follow transversus abdominis release as previously predicted.

Intravital Imaging Allows Organ-Specific Insights Into Immune Functions

Leukocytes are among the most mobile and versatile cells that have many essential functions in homeostasis and survival. Especially cells from the innate immune system, i.e., neutrophils and macrophages, play an important role as rapid first responders against invading microorganisms. With the advent of novel imaging techniques, new ways of visualizing innate immune cells have become available in recent years, thereby enabling more and more detailed discoveries about their nature, function and interaction partners. Besides intravital spinning-disc and 2-photon microscopy, clearing and 3D-imaging techniques provide new insights into the mechanism of innate immune cell behavior in their natural environment. This mini review focuses on the contributions of novel-imaging techniques to provide insight into the functions of neutrophils and macrophages under homeostasis and in infections. Imaging setups for different organs like the liver, kidney, heart, lung, and the peritoneal cavity are discussed as well as the current limitations of these imaging techniques.

Staphylococcus aureus Host Tropism and Its Implications for Murine Infection Models

Staphylococcus aureus (S. aureus) is a pathobiont of humans as well as a multitude of animal species. The high prevalence of multi-resistant and more virulent strains of S. aureus necessitates the development of new prevention and treatment strategies for S. aureus infection. Major advances towards understanding the pathogenesis of S. aureus diseases have been made using conventional mouse models, i.e., by infecting naïve laboratory mice with human-adapted S.aureus strains. However, the failure to transfer certain results obtained in these murine systems to humans highlights the limitations of such models. Indeed, numerous S. aureus vaccine candidates showed promising results in conventional mouse models but failed to offer protection in human clinical trials. These limitations arise not only from the widely discussed physiological differences between mice and humans, but also from the lack of attention that is paid to the specific interactions of S. aureus with its respective host. For instance, animal-derived S. aureus lineages show a high degree of host tropism and carry a repertoire of host-specific virulence and immune evasion factors. Mouse-adapted S.aureus strains, humanized mice, and microbiome-optimized mice are promising approaches to overcome these limitations and could improve transferability of animal experiments to human trials in the future.