Deep Sternal Wound Infection Caused by Rhizopus Species After Coronary Artery Bypass Graft.

Deep sternal wound infection is a rare complication of cardiac surgery that is typically caused by skin resident flora, such as species of Staphylococcus and Streptococcus. Infections caused by fungi are less common and are generally caused by Candida species. Regardless of etiology, these infections are associated with significant morbidity and mortality. We present a case of postoperative mediastinitis that occurred following a 5-vessel coronary artery bypass graft and was caused by a filamentous fungus of the Rhizopus genus. The patient was treated with serial debridement, liposomal amphotericin B, and isavuconazonium and was discharged from the hospital in stable condition. Fungal mediastinitis is a rare entity, and clinicians must maintain a high level of suspicion to make the diagnosis. A fungal cause of postoperative mediastinitis should be considered in patients with negative bacterial cultures, uncontrolled diabetes, or current immunosuppression or those who present weeks after surgery with a subacute onset of symptoms.

The immunology of the post-cardiac arrest syndrome.

Patients successfully resuscitated from cardiac arrest often have brain injury, myocardial dysfunction, and systemic ischemia-reperfusion injury, collectively termed the post-cardiac arrest syndrome (PCAS). To improve outcomes, potential therapies must be able to be administered early in the post-arrest course and provide broad cytoprotection, as ischemia-reperfusion injury affects all organ systems. Our understanding of the immune system contributions to the PCAS has expanded, with animal models detailing biologically plausible mechanisms of secondary injury, the protective effects of available immunomodulatory drugs, and how immune dysregulation underlies infection susceptibility after arrest. In this narrative review, we discuss the dysregulated immune response in PCAS, human trials of targeted immunomodulation therapies, and future directions for immunomodulation following cardiac arrest.

Hydroxocobalamin in Refractory Septic Shock: A Retrospective Case Series.

Refractory septic shock is associated with high morbidity and mortality. Hydroxocobalamin is used to treat postoperative vasoplegia; however, data supporting its use in the setting of refractory septic shock is limited and restricted to case reports. This study evaluates the effect of hydroxocobalamin on mean arterial pressure and vasopressor requirements in a series of patients with refractory septic shock. DESIGN: Single-center, retrospective analysis. SETTING: Urban, tertiary-care ICU. PATIENTS: Adult ICU patients with refractory septic shock treated with hydroxocobalamin between August 2018 and January 2020. INTERVENTIONS: Hydroxocobalamin 5 g IV infusion. MEASUREMENTS AND MAIN RESULTS: Twenty-six patients were included for the analysis. Administration of hydroxocobalamin was associated with an increase in mean arterial pressure at 1, 6, and 24 hours postdose (+16.3, +14.3, and +16.3 mm Hg, respectively; p < 0.001). Increase in mean arterial pressure from baseline remained statistically significant when controlling for sex, age, and comorbid conditions. There was no change in the norepinephrine equivalents patients required 1 hour following hydroxocobalamin administration, but a statistically significant decrease in norepinephrine equivalent was observed at 6 and 24 hours postdose (p < 0.001). CONCLUSIONS: Hydroxocobalamin provides sustained hemodynamic benefit at 24 hours in patients with refractory septic shock.

Cutting Edge: Glycolytic Metabolism and Mitochondrial Metabolism Are Uncoupled in Antigen-Activated CD8+ Recent Thymic Emigrants.

Recent thymic emigrants (RTEs) are peripheral T cells that have most recently completed selection and thymic egress and constitute a population that is phenotypically and functionally distinct from its more mature counterpart. Ag-activated RTEs are less potent effectors than are activated mature T cells, due in part to reduced aerobic glycolysis (correctable by exogenous IL-2), which in turn impacts IFN-γ production. Mitochondria serve as nodal regulators of cell function, but their contribution to the unique biology of RTEs is unknown. In this study, we show that activated mouse RTEs have impaired oxidative phosphorylation, even in the presence of exogenous IL-2. This altered respiratory phenotype is the result of decreased CD28 signaling, reduced glutaminase induction, and diminished mitochondrial mass in RTEs relative to mature T cells. These results suggest an uncoupling whereby IL-2 tunes the rate of RTE glycolytic metabolism, whereas the unique profile of RTE mitochondrial metabolism is "hard wired."

Reinterpreting recent thymic emigrant function: defective or adaptive?

Recent thymic emigrants (RTEs) are those peripheral T cells that have most recently completed thymic development and egress. Over the past decade, significant advances have been made in understanding the cell-extrinsic and cell-intrinsic requirements for RTE maturation to mature naïve (MN) T cells and in detailing the functional differences that characterize these two T cell populations. Much of this work has suggested that RTEs are hypo-functional versions of more mature T cells. However, recent evidence has indicated that rather than being defective T cells, RTEs are exquisitely adapted to their cellular niche. In this review, we argue that RTEs are not flawed mature T cells but are adapted to fill an underpopulated T cell compartment, while maintaining self tolerance and possessing the capacity to mount robust immune responses.

Cutting Edge: Defective Aerobic Glycolysis Defines the Distinct Effector Function in Antigen-Activated CD8+ Recent Thymic Emigrants.

Recent thymic emigrants (RTEs) are the youngest peripheral T cells that have completed thymic selection and egress to the lymphoid periphery. RTEs are functionally distinct from their more mature but still naive T cell counterparts, because they exhibit dampened proliferation and reduced cytokine production upon activation. In this article, we show that, compared with more mature but still naive T cells, RTEs are impaired in their ability to perform aerobic glycolysis following activation. Impaired metabolism underlies the reduced IFN-γ production observed in activated RTEs. This failure to undergo Ag-induced aerobic glycolysis is caused by reduced mTORC1 activity and diminished Myc induction in RTEs. Critically, exogenous IL-2 restores Myc expression in RTEs, driving aerobic glycolysis and IFN-γ production to the level of mature T cells. These results reveal a previously unknown metabolic component to postthymic T cell maturation.

POSH Regulates CD4+ T Cell Differentiation and Survival.

The scaffold molecule POSH is crucial for the regulation of proliferation and effector function in CD8(+) T cells. However, its role in CD4(+) T cells is not known. In this study, we found that disruption of the POSH scaffold complex established a transcriptional profile that strongly skewed differentiation toward Th2, led to decreased survival, and had no effect on cell cycle entry. This is in stark contrast to CD8(+) T cells in which POSH regulates cell cycle and does not affect survival. Disruption of POSH in CD4(+) T cells resulted in the loss of Tak1-dependent activation of JNK1/2 and Tak1-mediated survival. However, in CD8(+) T cells, POSH regulates only JNK1. Remarkably, each type of T cell had a unique composition of the POSH scaffold complex and distinct posttranslational modifications of POSH. These data indicate that the mechanism that regulates POSH function in CD4(+) T cells is different from CD8(+) T cells. All together, these data strongly suggest that POSH is essential for the integration of cell-type-specific signals that regulate the differentiation, survival, and function of T cells.

FTOC-Based Analysis of Negative Selection.

Potentially harmful T cell precursors are removed from the conventional T cell pool by negative selection. This process can involve the induction of apoptosis, anergy, receptor editing or deviation into a regulatory T cell lineage. As such this process is essential for the health of an organism through its contribution to central and peripheral tolerance. While a great deal is known about the process, the precise mechanisms that regulate negative selection are not clear. Furthermore, the signals that distinguish the different forms of negative selection are not fully understood. Numerous models exist with the potential to address these questions in vitro and in vivo. This chapter describes methods of fetal thymic organ culture designed to analyze the signals that determine these unique cell fates.

In Vitro Analysis of Thymocyte Signaling.

From the moment a developing thymocyte expresses a TCR, it is subjected to numerous interactions with self-peptide/MHC complexes that determine its ultimate fate. These include death by neglect, negative selection (apoptosis and lineage deviation), positive selection, and lineage commitment. The identification of signals that govern these unique cell fates requires the ability to assess the activity, level of expression, subcellular location, and the molecular associations of numerous proteins within the developing T cell. Thus, this chapter describes methods designed to analyze thymocyte signaling under various types of peptide-based stimulation in vitro.

The POSH/JIP-1 scaffold network regulates TCR-mediated JNK1 signals and effector function in CD8(+) T cells.

Signals from the T-cell recognition of antigen program effector functions are necessary to clear infections and tumors. The JNK pathway is critically important in regulating this process. In T lymphocytes, JNK1 and JNK2 have distinct functions depending on their maturation state and cell-type. However, the mechanisms that regulate their isoform-specific activity and function are still unclear. Here, we identify plenty of SH3 (POSH) and JNK-interacting protein 1 (JIP-1) as a multiprotein scaffold network for TCR-mediated JNK1 activation in CD8(+) T cells. Disruption of the POSH/JIP-1 complex led to profound defects in the activation of JNK1, as well as deficient activation or induction of the transcription factors c-Jun, T-bet, and Eomesodermin. Furthermore, disruption of the POSH/JIP complex in CD8(+) T cells resulted in impaired proliferation, decreased cytokine expression, and the inability to control tumors. Collectively, these data identify a mechanism for the specific regulation of TCR-dependent JNK1 activation and function that is key for CD8(+) T-cell responses.

Low-affinity T cells are programmed to maintain normal primary responses but are impaired in their recall to low-affinity ligands.

T cell responses to low-affinity T cell receptor (TCR) ligands occur in the context of infection, tumors, and autoimmunity despite diminished TCR signal strength. The processes that enable such responses remain unclear. We show that distinct mechanisms drive effector/memory development in high- and low-affinity T cells. Low-affinity cells preferentially differentiate into memory precursors of a central memory phenotype that are interleukin (IL)-12R(lo), IL-7R(hi), and Eomes(hi). Strikingly, in contrast to naive cells, low-affinity memory cells were impaired in the response to low- but not high-affinity ligands, indicating that low-affinity cells are programmed to generate diverse immune responses while avoiding autoreactivity. Affinity and antigen dose directly correlated with IL-12R signal input and T-bet but not with Eomes expression because low- affinity signals were more potent inducers of Eomes at a high antigen dose. Our studies explain how weak antigenic signals induce complete primary immune responses and provide a framework for therapeutic intervention.