Endothelial Cell Proteomic Response to Rickettsia conorii Infection Reveals Activation of the Janus Kinase (JAK)-Signal Transducer and Activator of Transcription (STAT)-Inferferon Stimulated Gene (ISG)15 Pathway and Reprogramming Plasma Membrane Integrin/Cadherin Signaling

Rickettsia conorii is the etiologic agent of Mediterranean spotted fever, a re-emerging infectious disease with significant mortality. This Gram-negative, obligately intracellular pathogen is transmitted via tick bites, resulting in disseminated vascular endothelial cell infection with vascular leakage. In the infected human, Rickettsia conorii infects endothelial cells, stimulating expression of cytokines and pro-coagulant factors. However, the integrated proteomic response of human endothelial cells to R. conorii infection is not known. In this study, we performed quantitative proteomic profiling of primary human umbilical vein endothelial cells (HUVECs) with established R conorii infection versus those stimulated with endotoxin (LPS) alone. We observed differential expression of 55 proteins in HUVEC whole cell lysates. Of these, we observed induction of signal transducer and activator of transcription (STAT)1, MX dynamin-like GTPase (MX1), and ISG15 ubiquitin-like modifier, indicating activation of the JAK-STAT signaling pathway occurs in R. conorii-infected HUVECs. The down-regulated proteins included those involved in the pyrimidine and arginine biosynthetic pathways. A highly specific biotinylated cross-linking enrichment protocol was performed to identify dysregulation of 11 integral plasma membrane proteins that included up-regulated expression of a sodium/potassium transporter and down-regulation of α-actin 1. Analysis of Golgi and soluble Golgi fractions identified up-regulated proteins involved in platelet-endothelial adhesion, phospholipase activity, and IFN activity. Thirty four rickettsial proteins were identified with high confidence in the Golgi, plasma membrane, or secreted protein fractions. The host proteins associated with rickettsial infections indicate activation of interferon-STAT signaling pathways; the disruption of cellular adhesion and alteration of antigen presentation pathways in response to rickettsial infections are distinct from those produced by nonspecific LPS stimulation. These patterns of differentially expressed proteins suggest mechanisms of pathogenesis as well as methods for diagnosis and monitoring Rickettsia infections.

Discovery of novel cross-protective Rickettsia prowazekii T-cell antigens using a combined reverse vaccinology and in vivo screening approach

Rickettsial agents are some of the most lethal pathogens known to man. Among them, Rickettsia prowazekii is a select agent with potential use for bioterrorism; yet, there is no anti-Rickettsia vaccine commercially available. Owing to the obligate intracellular lifestyle of rickettsiae, CD8(+) T cells are indispensable for protective cellular immunity. Furthermore, T cells can mediate cross-protective immunity between different pathogenic Rickettsia, a finding consistent with the remarkable similarity among rickettsial genomes. However, Rickettsia T cell antigens remain unidentified. In the present study, we report an algorithm that allowed us to identify and validate four novel R. prowazekii vaccine antigen candidates recognized by CD8(+) T cells from a set of twelve in silico-defined protein targets. Our results highlight the importance of combining proteasome-processing as well as MHC class-I-binding predictions. The novel rickettsial vaccine candidate antigens, RP778, RP739, RP598, and RP403, protected mice against a lethal challenge with Rickettsia typhi, which is indicative of cross-protective immunity within the typhus group rickettsiae. Together, our findings validate a reverse vaccinology approach as a viable strategy to identify protective rickettsial antigens and highlight the feasibility of a subunit vaccine that triggers T-cell-mediated cross-protection among diverse rickettsiae.

A human lung xenograft mouse model of Nipah virus infection

Nipah virus (NiV) is a member of the genus Henipavirus (family Paramyxoviridae) that causes severe and often lethal respiratory illness and encephalitis in humans with high mortality rates (up to 92%). NiV can cause Acute Lung Injury (ALI) in humans, and human-to-human transmission has been observed in recent outbreaks of NiV. While the exact route of transmission to humans is not known, we have previously shown that NiV can efficiently infect human respiratory epithelial cells. The molecular mechanisms of NiV-associated ALI in the human respiratory tract are unknown. Thus, there is an urgent need for models of henipavirus infection of the human respiratory tract to study the pathogenesis and understand the host responses. Here, we describe a novel human lung xenograft model in mice to study the pathogenesis of NiV. Following transplantation, human fetal lung xenografts rapidly graft and develop mature structures of adult lungs including cartilage, vascular vessels, ciliated pseudostratified columnar epithelium, and primitive “air” spaces filled with mucus and lined by cuboidal to flat epithelium. Following infection, NiV grows to high titers (10⁷ TCID₅₀/gram lung tissue) as early as 3 days post infection (pi). NiV targets both the endothelium as well as respiratory epithelium in the human lung tissues, and results in syncytia formation. NiV infection in the human lung results in the production of several cytokines and chemokines including IL-6, IP-10, eotaxin, G-CSF and GM-CSF on days 5 and 7 pi. In conclusion, this study demonstrates that NiV can replicate to high titers in a novel in vivo model of the human respiratory tract, resulting in a robust inflammatory response, which is known to be associated with ALI. This model will facilitate progress in the fundamental understanding of henipavirus pathogenesis and virus-host interactions; it will also provide biologically relevant models for other respiratory viruses.

Nipah virus (NiV) is a highly pathogenic zoonotic virus that causes fatal disease in humans and a variety of other mammalian hosts including pigs. Given the lack of effective therapeutics and vaccines, this virus is considered a public health and agricultural concern, and listed as category C priority pathogen for biodefense research by the National Institute of Allergy and Infectious Diseases. Both animal-to-human and human-to-human transmission has been observed. Studies on the molecular mechanisms of NiV-mediated pathogenesis have been hampered by the lack of biologically relevant in vivo models for studying the initial host responses to NiV infection in the human lung. We show here a new small animal model in which we transplant human lung tissue for studying the pathogenesis of NiV. We showed that NiV can replicate to high levels in the human lung. NiV causes extensive damage to the lung tissue and induces important regulators of the inflammatory response. This study is the first to use a human lung transplant for studying infectious diseases, a powerful model for studying the pathogenesis of NiV infection, and will open up new possibilities for studying virus-host interactions.

Cellular receptors for foot and mouth disease virus

Foot-and-mouth disease virus (FMDV), the prototype member of the Aphthovirus genus, is a single-stranded, positive-sense RNA genome virus, which affects many domestic livestock cloven-hoofed animals, causing substantial lost of milk in dairy cattle, reduction in the growth rate of meat animals, among others. It has been shown that the virus can enter to the cells using different pathways; the main one binding integrins via the clathrin-mediated endocytosis pathway, trafficking throughout the acidified endocytic vesicles, where its capsid rapidly dissociates, resulting in the release of the RNA genome, and the second one using heparan sulfate in which FMDV enters to the cells using the caveola-mediated endocytosis pathway and that caveolae can associate and traffic with endosomes. Different integrins had been involved as FMDV receptors (alphavbeta1, alphavbeta3, alpha5beta1, alphavbeta6, alphavbeta8); this review will try to resume the basic information about FMDV receptors from the last years to the present and will resume the most important in vitro and in vivo studies to elucidate the role of this receptor on the infection.