Critical role for the chemokine receptor CXCR6 in NK cell-mediated antigen-specific memory of haptens and viruses.

Hepatic natural killer (NK) cells mediate antigen-specific contact hypersensitivity (CHS) in mice deficient in T cells and B cells. We report here that hepatic NK cells, but not splenic or naive NK cells, also developed specific memory of vaccines containing antigens from influenza, vesicular stomatitis virus (VSV) or human immunodeficiency virus type 1 (HIV-1). Adoptive transfer of virus-sensitized NK cells into naive recipient mice enhanced the survival of the mice after lethal challenge with the sensitizing virus but not after lethal challenge with a different virus. NK cell memory of haptens and viruses depended on CXCR6, a chemokine receptor on hepatic NK cells that was required for the persistence of memory NK cells but not for antigen recognition. Thus, hepatic NK cells can develop adaptive immunity to structurally diverse antigens, an activity that requires NK cell-expressed CXCR6.

Antigen availability determines CD8⁺ T cell-dendritic cell interaction kinetics and memory fate decisions.

T cells are activated by antigen (Ag)-bearing dendritic cells (DCs) in lymph nodes in three phases. The duration of the initial phase of transient, serial DC-T cell interactions is inversely correlated with Ag dose. The second phase, characterized by stable DC-T cell contacts, is believed to be necessary for full-fledged T cell activation. Here we have shown that this is not the case. CD8⁺ T cells interacting with DCs presenting low-dose, short-lived Ag did not transition to phase 2, whereas higher Ag dose yielded phase 2 transition. Both antigenic constellations promoted T cell proliferation and effector differentiation but yielded different transcriptome signatures at 12 hr and 24 hr. T cells that experienced phase 2 developed long-lived memory, whereas conditions without stable contacts yielded immunological amnesia. Thus, T cells make fate decisions within hours after Ag exposure, resulting in long-term memory or abortive effector responses, correlating with T cell-DCs interaction kinetics.

T cell sensing of antigen dose governs interactive behavior with dendritic cells and sets a threshold for T cell activation.

After homing to lymph nodes, CD8+ T cells are primed by dendritic cells (DCs) in three phases. During phase one, T cells undergo brief serial contacts with DCs for several hours, whereas phase two is characterized by stable T cell-DC interactions. We show here that the duration of phase one and T cell activation kinetics correlated inversely with the number of complexes of cognate peptide and major histocompatibility complex (pMHC) per DC and with the density of antigen-presenting DCs per lymph node. Very few pMHC complexes were necessary for the induction of full-fledged T cell activation and effector differentiation. However, neither T cell activation nor transition to phase two occurred below a threshold antigen dose determined in part by pMHC stability. Thus, phase one permits T cells to make integrated 'measurements' of antigen dose that determine subsequent T cell participation in immune responses.

Adaptive immune responses mediated by natural killer cells.

Adaptive immunity has traditionally been considered a unique feature of vertebrate physiology. Unlike innate immune responses, which remain essentially unchanged upon exposure to a recurrent challenge with the same stimulus, adaptive immune cells possess the ability to learn and remember. Thus, secondary adaptive responses to a previously encountered challenge are qualitatively and/or quantitatively distinct from those elicited by a primary encounter. Besides this capacity to acquire long-lived memory, the second cardinal feature of adaptive immunity is antigen specificity. It has been generally believed that only T and B cells can develop antigen-specific immunologic memory, because these lymphocytes uniquely express recombination-activating gene (RAG) proteins, which are necessary for somatic rearrangement of V(D)J gene segments to assemble diverse antigen-specific receptors. However, recent work has uncovered discrete subsets of murine natural killer (NK) cells capable of mediating long-lived, antigen-specific recall responses to a variety of hapten-based contact sensitizers. These NK cells appear to use distinct, RAG-independent mechanisms to generate antigen specificity. Murine NK cells have also recently been shown to develop memory upon viral infection. Here, we review recent evidence indicating that at least some NK cells are capable of mediating what appears to be adaptive immunity and discuss potential mechanisms that may contribute to RAG-independent generation of antigenic diversity and longevity.

Targeted Proteomic Profiling of Cardiogenic Shock in the Cardiac Intensive Care Unit.

BACKGROUND: We sought to characterize circulating protein biomarkers associated with cardiogenic shock (CS) using highly multiplex proteomic profiling. METHODS: This analysis employed a cross-sectional case-control study design using a biorepository of patients admitted to a cardiac intensive care unit between 2017-2020. Cases were patients adjudicated to have CS and controls were those presenting for cardiac critical care without shock, including subsets of patients with isolated hypotension or heart failure (HF). The Olink platform was used to analyze 359 biomarkers with Bonferroni correction. RESULTS: The analysis included 239 patients presenting for cardiac critical care (69 cases with CS, 170 non-shock controls). A total of 63 biomarkers (17.7%) were significantly associated with CS after Bonferroni correction compared with all controls. Of these, nine biomarkers remained significantly associated with CS when separately cross-validated in subsets of controls presenting with isolated hypotension and HF: cathepsin D, fibroblast growth factor (FGF)-21 and -23, growth differentiation factor (GDF)-15, insulin-like growth factor binding protein-1, N-terminal pro-B-type natriuretic peptide, osteopontin, oncostatin-M-specific receptor subunit beta (OSMR), and soluble ST2 protein (sST2). Four biomarkers were identified as providing complementary information for CS diagnosis with development of a multi-marker model: sST2, FGF-23, CTSD, and GDF-15. CONCLUSION: In this pilot study of targeted proteomic profiling in CS, we identified nine biomarkers significantly associated with CS when cross-validated against non-shock controls including those with HF or isolated hypotension, illustrating the potential application of a targeted proteomic approach to identify novel candidates that may support the diagnosis of CS.

Need for a Cardiogenic Shock Team Collaborative-Promoting a Team-Based Model of Care to Improve Outcomes and Identify Best Practices.

Cardiogenic shock continues to carry a high mortality rate despite contemporary care, with no breakthrough therapies shown to improve survival over the past few decades. It is a time-sensitive condition that commonly results in cardiovascular complications and multisystem organ failure, necessitating multidisciplinary expertise. Managing patients with cardiogenic shock remains challenging even in well-resourced settings, and an important subgroup of patients may require cardiac replacement therapy. As a result, the idea of leveraging the collective cognitive and procedural proficiencies of multiple providers in a collaborative, team-based approach to care (the "shock team") has been advocated by professional societies and implemented at select high-volume clinical centers. A slowly maturing evidence base has suggested that cardiogenic shock teams may improve patient outcomes. Although several registries exist that are beginning to inform care, particularly around therapeutic strategies of pharmacologic and mechanical circulatory support, none of these are currently focused on the shock team approach, multispecialty partnership, education, or process improvement. We propose the creation of a Cardiogenic Shock Team Collaborative-akin to the successful Pulmonary Embolism Response Team Consortium-with a goal to promote sharing of care protocols, education of stakeholders, and discovery of how process and performance may influence patient outcomes, quality, resource consumption, and costs of care.

Epidemiology and Management of ST-Segment-Elevation Myocardial Infarction in Patients With COVID-19: A Report From the American Heart Association COVID-19 Cardiovascular Disease Registry.

Background Early reports from the COVID-19 pandemic identified coronary thrombosis leading to ST-segment-elevation myocardial infarction (STEMI) as a complication of COVID-19 infection. However, the epidemiology of STEMI in patients with COVID-19 is not well characterized. We sought to determine the incidence, diagnostic and therapeutic approaches, and outcomes in STEMI patients hospitalized for COVID-19. Methods and Results Patients with data on presentation ECG and in-hospital myocardial infarction were identified from January 14, 2020 to November 30, 2020, from 105 sites participating in the American Heart Association COVID-19 Cardiovascular Disease Registry. Patient characteristics, resource use, and clinical outcomes were summarized and compared based on the presence or absence of STEMI. Among 15 621 COVID-19 hospitalizations, 54 (0.35%) patients experienced in-hospital STEMI. Among patients with STEMI, the majority (n=40, 74%) underwent transthoracic echocardiography, but only half (n=27, 50%) underwent coronary angiography. Half of all patients with COVID-19 and STEMI (n=27, 50%) did not undergo any form of primary reperfusion therapy. Rates of all-cause shock (47% versus 14%), cardiac arrest (22% versus 4.8%), new heart failure (17% versus 1.4%), and need for new renal replacement therapy (11% versus 4.3%) were multifold higher in patients with STEMI compared with those without STEMI (P<0.050 for all). Rates of in-hospital death were 41% in patients with STEMI, compared with 16% in those without STEMI (P<0.001). Conclusions STEMI in hospitalized patients with COVID-19 is rare but associated with poor in-hospital outcomes. Rates of coronary angiography and primary reperfusion were low in this population of patients with STEMI and COVID-19. Adaptations of systems of care to ensure timely contemporary treatment for this population are needed.

In vivo imaging of T cell priming.

The rules by which naïve T cells decide whether and how to respond to antigenic stimuli are incompletely understood. Using multiphoton intravital microscopy (MP-IVM) in lymph nodes (LNs), we have shown that CD8+ T cells are primed by antigen-presenting dendritic cells (DCs) in three consecutive phases. During phase one, T cells undergo brief serial contacts with many DCs for several hours after homing into the LNs. Subsequently, during phase two, T cells engage in prolonged stable interactions with DCs. Finally, in the third phase, T cells return to transient interactions with DCs as they begin to proliferate and eventually leave the LNs. We have examined the influence of antigen dose on the duration of phase one by systematically varying both the number of cognate peptide-major histocompatability (pMHC) complexes per DC and the density of cognate pMHC complex-presenting DCs per LN. The duration of phase one and the kinetics of CD8+ T cell activation were inversely correlated with both parameters. Very few pMHC complexes were needed for full T cell activation and effector differentiation. Furthermore, there was a sharp threshold of antigen dose below which T cells did not transition to phase two but continued to migrate until they exited the LN, unactivated. The stability of peptide binding to MHC was a critical determinant of this threshold antigen dose in vivo. Our results suggest an integrative mechanism that allows T cells to reach an informed decision about whether to respond, based on the overall antigen dose encountered.

Generation of gut-homing IgA-secreting B cells by intestinal dendritic cells.

Normal intestinal mucosa contains abundant immunoglobulin A (IgA)-secreting cells, which are generated from B cells in gut-associated lymphoid tissues (GALT). We show that dendritic cells (DC) from GALT induce T cell-independent expression of IgA and gut-homing receptors on B cells. GALT-DC-derived retinoic acid (RA) alone conferred gut tropism but could not promote IgA secretion. However, RA potently synergized with GALT-DC-derived interleukin-6 (IL-6) or IL-5 to induce IgA secretion. Consequently, mice deficient in the RA precursor vitamin A lacked IgA-secreting cells in the small intestine. Thus, GALT-DC shape mucosal immunity by modulating B cell migration and effector activity through synergistically acting mediators.