Steven L. Raymond

Microbial recognition and danger signals in sepsis and trauma

Early host recognition of microbial invasion or damaged host tissues provides an effective warning system by which protective immune and inflammatory processes are initiated. Host tissues responsible for continuous sampling of their local environment employ cell surface and cytosolic pattern recognition receptors (PRRs) that provide redundant and overlapping identification of both microbial and host alarmins. Microbial products containing pathogen-associated molecular patterns (PAMPs), as well as damage-associated molecular patterns (DAMPs) serve as principle ligands for recognition by these PRRs. It is this interaction which plays both an essential survival role in response to infection and injury, as well as the pathologic role in tissue and organ injury associated with severe sepsis and trauma. Elucidating the interaction between ligands and their respective PRRs can provide both a better understanding of the host response, as well as a rational basis for therapeutic intervention. This article is part of a Special Issue entitled: Immune and Metabolic Alterations in Trauma and Sepsis edited by Dr. Raghavan Raju.

Murine Models of Sepsis and Trauma: Can We Bridge the Gap?

Sepsis and trauma are both leading causes of death in the United States and represent major public health challenges. Murine models have largely been used in sepsis and trauma research to better understand the pathophysiological changes that occur after an insult and to develop potential life-saving therapeutic agents. Mice are favorable subjects for this type of research given the variety of readily available strains including inbred, outbred, and transgenic strains. In addition, they are relatively easy to maintain and have a high fecundity. However, pharmacological therapies demonstrating promise in preclinical mouse models of sepsis and trauma often fail to demonstrate similar efficacy in human clinical trials, prompting considerable criticism surrounding the capacity of murine models to recapitulate complex human diseases like sepsis and traumatic injury. Fundamental differences between the two species include, but are not limited to, the divergence of the transcriptomic response, the mismatch of temporal response patterns, differences in both innate and adaptive immunity, and heterogeneity within the human population in comparison to the homogeneity of highly inbred mouse strains. Given the ongoing controversy, this narrative review aims to not only highlight the historical importance of the mouse as an animal research model but also highlight the current benefits and limitations of the model as it pertains to sepsis and trauma. Lastly, this review will propose future directions that may promote further use of the model.

Immunological Defects in Neonatal Sepsis and Potential Therapeutic Approaches

Despite advances in critical care medicine, neonatal sepsis remains a major cause of morbidity and mortality worldwide, with the greatest risk affecting very low birth weight, preterm neonates. The presentation of neonatal sepsis varies markedly from its presentation in adults, and there is no clear consensus definition of neonatal sepsis. Previous work has demonstrated that when neonates become septic, death can occur rapidly over a matter of hours or days and is generally associated with inflammation, organ injury, and respiratory failure. Studies of the transcriptomic response by neonates to infection and sepsis have led to unique insights into the early proinflammatory and host protective responses to sepsis. Paradoxically, this early inflammatory response in neonates, although lethal, is clearly less robust relative to children and adults. Similarly, the expression of genes involved in host protective immunity, particularly neutrophil function, is also markedly deficient. As a result, neonates have both a diminished inflammatory and protective immune response to infection which may explain their increased risk to infection, and their reduced ability to clear infections. Such studies imply that novel approaches unique to the neonate will be required for the development of both diagnostics and therapeutics in this high at-risk population.

Neutrophil chemotaxis and transcriptomics in term and preterm neonates

&NA; Neutrophils play a crucial role in combating life‐threatening bacterial infections in neonates. Previous studies investigating neonatal cell function have been limited because of restricted volume sampling. Here, using novel microfluidic approaches, we provide the first description of neutrophil chemotaxis and transcriptomics from whole blood of human term and preterm neonates, as well as young adults. Ex vivo percent cell migration, neutrophil velocity, and directionality to N‐formylmethionyl‐leucyl‐phenylalanine were measured from whole blood using time‐lapse imaging of microfluidic chemotaxis. Genome‐wide expression was also evaluated in CD66b+ cells using microfluidic capture devices. Neutrophils from preterm neonates migrated in fewer numbers compared to term neonates (preterm 12.3%, term 30.5%, P = 0.008) and at a reduced velocity compared to young adults (preterm 10.1 &mgr;m/min, adult 12.7 &mgr;m/min, P = 0.003). Despite fewer neutrophils migrating at slower velocities, neutrophil directionality from preterm neonates was comparable to adults and term neonates. 3607 genes were differentially expressed among the 3 groups (P < 0.001). Differences in gene expression between neutrophils from preterm and term neonates were consistent with reduced pathogen recognition and antimicrobial activity but not neutrophil migration, by preterm neonates. In summary, preterm neonates have significant disturbances in neutrophil chemotaxis compared to term neonates and adults, and these differences in phenotype appear at the transcriptional level to target inflammatory pathways in general, rather than in neutrophil migration and chemotaxis.

Unique transcriptomic response to sepsis is observed among patients of different age groups

Sepsis is a major cause of morbidity and mortality, especially at the extremes of age. To understand the human age-specific transcriptomic response to sepsis, a multi-cohort, pooled analysis was conducted on adults, children, infants, and neonates with and without sepsis. Nine public whole-blood gene expression datasets (636 patients) were employed. Age impacted the transcriptomic host response to sepsis. Gene expression from septic neonates and adults was more dissimilar whereas infants and children were more similar. Neonates showed reductions in inflammatory recognition and signaling pathways compared to all other age groups. Likewise, adults demonstrated decreased pathogen sensing, inflammation, and myeloid cell function, as compared to children. This may help to explain the increased incidence of sepsis-related organ failure and death in adults. The number of dysregulated genes in septic patients was proportional to age and significantly differed among septic adults, children, infants, and neonates. Overall, children manifested a greater transcriptomic intensity to sepsis as compared to the other age groups. The transcriptomic magnitude for adults and neonates was dramatically reduced as compared to children and infants. These findings suggest that the transcriptomic response to sepsis is age-dependent, and diagnostic and therapeutic efforts to identify and treat sepsis will have to consider age as an important variable.

Impact of Early-Life Exposures to Infections, Antibiotics, and Vaccines on Perinatal and Long-term Health and Disease

Essentially, all neonates are exposed to infections, antibiotics, or vaccines early in their lives. This is especially true for those neonates born underweight or premature. In contrast to septic adults and children who are at an increased risk for subsequent infections, exposure to infection during the neonatal period is not associated with an increased risk of subsequent infection and may be paradoxically associated with reductions in late-onset sepsis (LOS) in the most premature infants. Perinatal inflammation is also associated with a decreased incidence of asthma and atopy later in life. Conversely, septic neonates are at increased risk of impaired long-term neurodevelopment. While the positive effects of antibiotics in the setting of infection are irrefutable, prolonged administration of broad-spectrum, empiric antibiotics in neonates without documented infection is associated with increased risk of LOS, necrotizing enterocolitis, or death. Vaccines provide a unique opportunity to prevent infection-associated disease; unfortunately, vaccinations have been largely unsuccessful when administered in the first month of life with the exception of vaccines against hepatitis B and tuberculosis. Future vaccines will require the use of novel adjuvants to overcome this challenge. This review describes the influence of infections, antibiotics, and vaccines during the first days of life, as well as the influence on future health and disease. We will also discuss potential immunomodulating therapies, which may serve to train the preterm immune system and reduce subsequent infectious burden without subjecting neonates to the risks accompanied by virulent pathogens.

Predicting appendiceal tumors among patients with appendicitis.

BACKGROUND As nonoperative management of appendicitis gains popularity, vigilance for appendiceal tumors becomes increasingly important. We hypothesized that, among patients presenting with acute appendicitis, those with advanced age, multiple comorbidities, atypical presentation, and complicated appendicitis would be more likely to have underlying appendiceal tumors. METHODS We performed a 4-year retrospective cohort analysis of 677 consecutive adult patients who underwent appendectomy for appendicitis at our tertiary care center. Patients with an appendiceal tumor on their final pathology report were compared to patients with no tumor. Conditions present on admission were used to create a multivariate logistic regression model to predict appendiceal tumor. Risk factors were reported as odds ratio (OR) [95% CI]. Model strength was assessed by area under the receiver operating characteristic curve. RESULTS Seventeen patients (2.5%) had an appendiceal tumor. Within this group. 14 underwent immediate appendectomy, two initially had nonoperative management but failed to improve on antibiotics and underwent appendectomy during the initial admission, and one had successful nonoperative management and elective appendectomy 19 days after discharge. Four variables contributed to the multivariate model to predict the presence appendiceal tumor: age ≥ 50 (OR 3.6 [1.1–11.4]), outpatient steroid/immunosuppressant use (OR 12.1 [2.0–72.5]), the absence of migratory right lower quadrant pain (OR 4.7 [1.2–18.1]), and the appearance of a phlegmon on CT scan (OR 7.0 [1.6–30.2]); model area under the receiver operating characteristic curve: 0.860 [0.705–0.969]. CONCLUSION For patients presenting with acute appendicitis, conditions present on admission may predict underlying appendiceal tumor. Patients with advanced age, multiple comorbidities, atypical presentation, and complicated appendicitis should be considered for appendectomy during the index admission or at earliest convenience if nonoperative management is necessary. LEVEL OF EVIDENCE Prognostic study, level III.

Laparoscopic sleeve gastrectomy in patients with heart failure and left ventricular assist devices as a bridge to transplant

BACKGROUND Obesity is an epidemic that is closely associated with heart failure. The ultimate treatment for end-stage heart failure is cardiac transplantation. Patients with morbid obesity are often excluded from receiving donor organs. Many transplant centers use body mass index (BMI) >35 kg/m2 as a contraindication to listing for heart transplant. Left ventricular assist devices (LVADs) were developed as a bridge to transplant for many heart failure patients, but bariatric surgery for LVAD patients has not been well described. OBJECTIVES The purpose of our study was to evaluate the safety and efficacy of laparoscopic sleeve gastrectomy (LSG) in LVAD patients and the impact on heart failure recovery as a bridge to cardiac transplantation. SETTING University hospital. METHODS A retrospective study was conducted to evaluate the outcomes of patients with morbid obesity and LVADs who underwent LSG at a large academic medical center between 2013 and 2017. Age, BMI, percent excess weight loss, cardiac ejection fraction, listing status for transplantation, and success of transplant were reviewed. RESULTS Eleven patients were identified with morbid obesity and heart failure with LVAD support who underwent LSG. There were no perioperative deaths. Four patients (37%) achieved BMI <35 and were successfully listed for and received cardiac transplantation. An additional 3 patients (27%) achieved BMI <35 kg/m2 and are listed for cardiac transplantation. CONCLUSIONS LSG can be safely used in patients with morbid obesity and end-stage heart failure requiring LVAD support to lower their BMI and become eligible for cardiac transplantation.

Innate Immunity in the Persistent Inflammation, Immunosuppression, and Catabolism Syndrome and Its Implications for Therapy

Clinical and technological advances promoting early hemorrhage control and physiologic resuscitation as well as early diagnosis and optimal treatment of sepsis have significantly decreased in-hospital mortality for many critically ill patient populations. However, a substantial proportion of severe trauma and sepsis survivors will develop protracted organ dysfunction termed chronic critical illness (CCI), defined as ≥14 days requiring intensive care unit (ICU) resources with ongoing organ dysfunction. A subset of CCI patients will develop the persistent inflammation, immunosuppression, and catabolism syndrome (PICS), and these individuals are predisposed to a poor quality of life and indolent death. We propose that CCI and PICS after trauma or sepsis are the result of an inappropriate bone marrow response characterized by the generation of dysfunctional myeloid populations at the expense of lympho- and erythropoiesis. This review describes similarities among CCI/PICS phenotypes in sepsis, cancer, and aging and reviews the role of aberrant myelopoiesis in the pathophysiology of CCI and PICS. In addition, we characterize pathogen recognition, the interface between innate and adaptive immune systems, and therapeutic approaches including immune modulators, gut microbiota support, and nutritional and exercise therapy. Finally, we discuss the future of diagnostic and prognostic approaches guided by machine and deep-learning models trained and validated on big data to identify patients for whom these approaches will yield the greatest benefits. A deeper understanding of the pathophysiology of CCI and PICS and continued investigation into novel therapies harbor the potential to improve the current dismal long-term outcomes for critically ill post-injury and post-infection patients.

Adjuvant pretreatment with alum protects neonatal mice in sepsis through myeloid cell activation

The high mortality in neonatal sepsis has been related to both quantitative and qualitative differences in host protective immunity. Pretreatment strategies to prevent sepsis have received inadequate consideration, especially in the premature neonate, where outcomes from sepsis are so dismal. Aluminium salts‐based adjuvants (alum) are used currently in many paediatric vaccines, but their use as an innate immune stimulant alone has not been well studied. We asked whether pretreatment with alum adjuvant alone could improve outcome and host innate immunity in neonatal mice given polymicrobial sepsis. Subcutaneous alum pretreatment improves survival to polymicrobial sepsis in both wild‐type and T and B cell‐deficient neonatal mice, but not in caspase‐1/11 null mice. Moreover, alum increases peritoneal macrophage and neutrophil phagocytosis, and decreases bacterial colonization in the peritoneum. Bone marrow‐derived neutrophils from alum‐pretreated neonates produce more neutrophil extracellular traps (NETs) and exhibit increased expression of neutrophil elastase (NE) after in‐vitro stimulation with phorbol esters. In addition, alum pretreatment increases bone marrow and splenic haematopoietic stem cell expansion following sepsis. Pretreatment of neonatal mice with an alum‐based adjuvant can stimulate multiple innate immune cell functions and improve survival. These novel findings suggest a therapeutic pathway for the use of existing alum‐based adjuvants for preventing sepsis in premature infants.