CXCR4 is a G protein-coupled chemokine receptor that has been implicated in the pathogenesis of primary immunodeficiency disorders and cancer. Autosomal dominant gain-of-function truncations of CXCR4 are associated with warts, hypogammaglobulinemia, infections, and myelokathexis (WHIM) syndrome, a primary immunodeficiency disorder characterized by neutropenia and recurrent infections. Recent progress has implicated CXCR4-SDF1 (stromal cell-derived factor 1) signaling in regulating neutrophil homeostasis, but the precise role of IntroductionStromal cell-derived factor 1 (SDF1, CXCL12)-mediated activation 1 of the chemokine receptor CXCR4 is important for both normal and pathologic processes, including primordial germ cell migration, HIV pathogenesis, invasive migration of cancer cells, and leukocyte trafficking. 2-5 Therefore, there is substantial interest in understanding how CXCR4-SDF1 signaling regulates cell motility and how these mechanisms can be targeted to treat human disease. CXCR4 signaling is attenuated by receptor internalization, which is regulated by phosphorylation events and binding of regulatory proteins to the cytoplasmic tail. 6 The functional importance of CXCR4 internalization is highlighted by the dominantly inherited primary immunodeficiency, warts, hypogammaglobulinemia, infections, and myelokathexis (WHIM) syndrome, in which truncations of CXCR4 lead to altered signaling and gain of function. [7][8][9] WHIM syndrome is characterized by warts, hypogammaglobulinemia, infections, and myelokathexis, a severe chronic neutropenia. 10,11 Substantial evidence supports the importance of CXCR4 signaling in regulating neutrophil homeostasis and release from the bone marrow (BM). 5 It has been postulated that the neutropenia in patients with WHIM syndrome results from both neutrophil retention in the BM and enhanced neutrophil apoptosis of retained neutrophils. 11 Direct evidence to support this hypothesis has been provided by a mouse model of WHIM syndrome induced by the ectopic expression of WHIM truncation mutations of CXCR4 in hematopoietic stem cells that show impaired neutrophil release into the blood and increased rates of apoptosis in the BM. 12 Previous reports indicate that neutrophils from patients with WHIM show increased signaling 13 and chemotaxis 8,9 in response to SDF1. However, some reports have suggested that the C-terminus of CXCR4 can both positively and negatively regulate cell motility 8,9,14 and, alternatively, may be involved in modulating the precise targeting of cells in vivo. 15 Despite the importance of CXCR4-SDF1 signaling, few animal models of WHIM syndrome are amenable to imaging or screening for drugs that modulate CXCR4-SDF1 function in vivo. Modeling WHIM syndrome is particularly attractive because CXCR4 signaling is important to many disease processes and is a direct result of aberrant chemokine signaling. Therefore, developing a model of WHIM syndrome in a system that allows the direct visualization of motility and chemotactic events in vivo would be a beneficial ...

SignificanceBoth highly pathogenic avian influenza virus and Middle East respiratory syndrome coronavirus (MERS-CoV) infections are characterized by severe disease and high mortality. The continued threat of their emergence from zoonotic populations underscores an important need to understand the dynamics of their infection. By comparing the host responses across other related respiratory virus infections, these studies have identified a common avenue used by MERS-CoV and A/influenza/Vietnam/1203/2004 (H5N1-VN1203) influenza to antagonize antigen presentation through epigenetic modulation. Overall, the use of cross-comparisons provides an additional approach to leverage systems biology data to identify key pathways and strategies used by viruses to subvert host immune responses and may be critical in developing both vaccines and therapeutic treatment.

The hallmark of chronic inflammation is the infiltration and persistence of leukocytes within inflamed tissue. Here, we describe the first zebrafish chronic inflammation mutant identified in an insertional mutagenesis screen for mutants that exhibit abnormal tissue distribution of neutrophils. We identified a mutant line with an insertion in the Hepatocyte growth factor activator inhibitor 1 gene (hai1; also known as Spint1) that showed accumulation of neutrophils in the fin. The mutant embryos exhibited inflammation in areas of epidermal hyperproliferation that was rescued by knock-down of the type II transmembrane serine protease Matriptase 1 (also known as St14), suggesting a novel role for Hai1-Matriptase 1 pathway in regulating inflammation. Using time-lapse microscopy of mutant embryos that express GFP from a neutrophil-specific promoter, we found that individual neutrophils in inflamed tissue displayed random motility characterized by periods of pausing alternating with periods of motility. During periods of persistent movement the cells were highly polarized, while the pausing modes were characterized by a loss of cell polarity. In contrast to responses to acute injury, neutrophils did not exhibit clear retrograde chemotaxis or resolution of inflammation in the mutant. These findings illustrate the utility of zebrafish as a new model system to study chronic inflammation and to visualize immune responses with high resolution in vivo.

SUMMARY The pathogenesis of Human Ebola virus disease (EVD) is complex. EVD is characterized by high levels of virus replication and dissemination, dysregulated immune responses, extensive virus- and host-mediated tissue damage, and disordered coagulation. To clarify how host responses contribute to EVD pathophysiology, we performed multi-platform ‘omics analysis of peripheral blood mononuclear cells and plasma from EVD patients. Our results indicate that EVD molecular signatures overlap with those of sepsis, imply that pancreatic enzymes contribute to tissue damage in fatal EVD, and suggest that EBOV infection may induce aberrant neutrophils whose activity could explain hallmarks of fatal EVD. Moreover, integrated biomarker prediction identified putative biomarkers from different data platforms that differentiated survivors and fatalities early after infection. This work reveals insight into EVD pathogenesis, suggests an effective approach for biomarker identification, and provides an important community resource for further analysis of human EVD severity.

Zebrafish have emerged as a powerful model system to study leukocyte recruitment and inflammation. Here we characterize the morphology and function of inflammatory macrophages in zebrafish larvae. These macrophages can be distinguished from neutrophils by immunolabeling of L-Plastin without MPO co-expression and by an elongated morphology. Live imaging of transgenic zMPO:GFP larvae demonstrate that GFPlo macrophages migrate to wounds by extension of thin pseudopods and carry out phagocytosis of tissue debris, and FACS analysis of leukocyte markers indicates expression of CSF1R in these macrophages. These findings identify distinct functional and morphological characteristics of inflammatory macrophages in zebrafish larvae.