Exploratory Evaluation of the Relationship Between iNKT Cells and Systemic Cytokine Profiles of Critically Ill Patients with Neurological Injury.

BACKGROUND: Neurological injury can alter the systemic immune system, modifying the functional capacity of immune cells and causing a dysfunctional balance of cytokines, although mechanisms remain incompletely understood. The objective of this study was to assess the temporal relationship between changes in the activation status of circulating invariant natural killer T (iNKT) cells and the balance of plasma cytokines among critically ill patients with neurological injury. METHODS: We conducted an exploratory prospective observational study of adult (18 years or older) intensive care unit (ICU) patients with acute neurological injury (n = 20) compared with ICU patients without neurological injury (n = 22) and healthy controls (n = 10). Blood samples were collected on days 1, 2, 4, 7, 14, and 28 following ICU admission to analyze the activation status of circulating iNKT cells by flow cytometry and the plasma concentration of inflammation-relevant immune mediators, including T helper 1 (TH1) and T helper 2 (TH2) cytokines, by multiplex bead-based assay. RESULTS: Invariant natural killer T cells were activated in both ICU patient groups compared with healthy controls. Neurological patients had decreased levels of multiple immune mediators, including TH1 cytokines (interferon-γ, tumor necrosis factor-α, and interleukin-12p70), indicative of immunosuppression. This led to a greater than twofold increase in the ratio of TH2/TH1 cytokines early after injury (days 1 - 2) compared with healthy controls, a shift that was also observed for ICU controls. Systemic TH2/TH1 cytokine ratios were positively associated with iNKT cell activation in the neurological patients and negatively associated in ICU controls. These relationships were strongest for the CD4+ iNKT cell subset compared with the CD4- iNKT cell subset. The relationships to individual cytokines similarly differed between patient groups. Forty percent of the neurological patients developed an infection; however, differences for the infection subgroup were not identified. CONCLUSIONS: Critically ill patients with neurological injury demonstrated altered systemic immune profiles early after injury, with an association between activated peripheral iNKT cells and elevated systemic TH2/TH1 cytokine ratios. This work provides further support for a brain-immune axis and the ability of neurological injury to have far-reaching effects on the body's immune system.

Unraveling the host's immune response to infection: Seeing is believing.

It has long been appreciated that understanding the interactions between the host and the pathogens that make us sick is critical for the prevention and treatment of disease. As antibiotics become increasingly ineffective, targeting the host and specific bacterial evasion mechanisms are becoming novel therapeutic approaches. The technology used to understand host-pathogen interactions has dramatically advanced over the last century. We have moved away from using simple in vitro assays focused on single-cell events to technologies that allow us to observe complex multicellular interactions in real time in live animals. Specifically, intravital microscopy (IVM) has improved our understanding of infection, from viral to bacterial to parasitic, and how the host immune system responds to these infections. Yet, at the same time it has allowed us to appreciate just how complex these interactions are and that current experimental models still have a number of limitations. In this review, we will discuss the advances in vivo IVM has brought to the study of host-pathogen interactions, focusing primarily on bacterial infections and innate immunity.

Incidence, prevalence, and occurrence rate of infection among adults hospitalized after traumatic brain injury: study protocol for a systematic review and meta-analysis.

BACKGROUND: Infection occurs commonly among patients hospitalized after traumatic brain injury (TBI) and has been associated with increased intensive care unit and hospital lengths of stay and an elevated risk of poor neurological outcome and mortality. However, as many relevant published studies to date have varied in the type and severity of TBI among included patients as well as in their design (randomized versus non-randomized), risk of bias, and setting (hospital ward versus intensive care unit), their reported estimates of infection occurrence vary considerably. Thus, the purpose of this systematic review and meta-analysis is to estimate the incidence, prevalence, and occurrence rate of infection among patients hospitalized after TBI. METHODS/DESIGN: We will search electronic bibliographic databases (MEDLINE, EMBASE, PubMed, Cumulative Index to Nursing and Allied Health Literature (CINAHL), Scopus, Web of Science, the Cochrane Central Register of Controlled Trials (CENTRAL), and the Cochrane Database of Systematic Reviews) from their first available date as well as personal files, reference lists of included articles, and conference proceedings. Two investigators will independently screen titles and abstracts and select cohort studies, cross-sectional studies, and randomized controlled trials involving adults hospitalized after TBI that reported estimates of cumulative incidence, incidence rate, prevalence, or occurrence rate of infection for inclusion in the systematic review. These investigators will also independently extract data and assess risk of bias. We will exclude studies with fewer than ten patients; experimental groups allocated to treatment with antibiotics, glucocorticoids, immunosuppressants, barbiturates, or hypothermia; and studies focused on military/combat-related TBI. Pooled estimates of cumulative incidence, incidence rate, prevalence, and occurrence rate will be calculated using random effects models. We will also calculate I2 and Cochran Q statistics to assess for inter-study heterogeneity and conduct stratified analyses and univariate meta-regression to determine the influence of pre-defined study-level covariates on our pooled estimates. DISCUSSION: This study will compile the world literature regarding the epidemiology of infection among adults hospitalized after TBI. A better understanding of the role of infection will be helpful in the development of guidelines for patient management. This protocol has been registered in the PROSPERO International Prospective Register of Systematic Reviews (ID: CRD42013005146).

Infection-induced NETosis is a dynamic process involving neutrophil multitasking in vivo.

Neutrophil extracellular traps (NETs) are released as neutrophils die in vitro in a process requiring hours, leaving a temporal gap that invasive microbes may exploit. Neutrophils capable of migration and phagocytosis while undergoing NETosis have not been documented. During Gram-positive skin infections, we directly visualized live polymorphonuclear cells (PMNs) in vivo rapidly releasing NETs, which prevented systemic bacterial dissemination. NETosis occurred during crawling, thereby casting large areas of NETs. NET-releasing PMNs developed diffuse decondensed nuclei, ultimately becoming devoid of DNA. Cells with abnormal nuclei showed unusual crawling behavior highlighted by erratic pseudopods and hyperpolarization consistent with the nucleus being a fulcrum for crawling. A requirement for both Toll-like receptor 2 and complement-mediated opsonization tightly regulated NET release. Additionally, live human PMNs injected into mouse skin developed decondensed nuclei and formed NETS in vivo, and intact anuclear neutrophils were abundant in Gram-positive human abscesses. Therefore early in infection NETosis involves neutrophils that do not undergo lysis and retain the ability to multitask.