ABSTRACT
Cells of the mononuclear and endothelial lineages are targets for viruses which cause hemorrhagic fevers (HF) such as the filoviruses Marburg and Ebola, and the arenaviruses Lassa and Junin. A recent model of Marburg HF pathogenesis proposes that virus directly causes endothelial cell damage and macrophage release of TNF-alpha which increases the permeability of endothelial monolayers [Feldmann et al. , 1996]. We show that Lassa virus replicates in human monocytes/macrophages and endothelial cells without damaging them. Human endothelial cells (HUVEC) are highly susceptible to infection by both Lassa and Mopeia (a non-pathogenic Lassa-related arenavirus). Whereas monocytes must differentiate into macrophages before supporting even low level production of these viruses, the virus yields in the culture medium of infected HUVEC cells reach more than 7 log10 PFU/ml without cellular damage. In contrast to filovirus, Lassa virus replication in monocytes/macrophages fails to stimulate TNF-alpha gene expression and even down-regulates LPS-stimulated TNF-alpha mRNA synthesis. The expression of IL-8, a prototypic proinflammatory CXC chemokine, was also suppressed in Lassa virus infected monocytes/macrophages and HUVEC on both the protein and mRNA levels. This contrasts with Mopeia virus infection of HUVEC in which neither IL-8 mRNA nor protein are reduced. The cumulative down-regulation of TNF-alpha and IL-8 expression could explain the absence of inflammatory and effective immune responses in severe cases of Lassa HF.
Subject(s)
Arenaviridae/physiology , Endothelium, Vascular/virology , Lassa virus/physiology , Macrophages/virology , Monocytes/virology , Virus Replication , Arenaviridae Infections/immunology , Arenaviridae Infections/virology , Cells, Cultured , Humans , Interleukin-8/genetics , Interleukin-8/metabolism , Lassa Fever/immunology , Lassa Fever/virology , Lipopolysaccharides/pharmacology , Monocytes/physiology , RNA, Messenger/metabolism , Tumor Necrosis Factor-alpha/genetics , Tumor Necrosis Factor-alpha/metabolism , Umbilical VeinsABSTRACT
Vero cells chronically infected with Lassa virus as well as BHK-21 cells chronically infected with Machupo virus produced particles interfering with the replication of homologous, but not heterogeneous viruses. RNAs of standard virus particles contained 4 sedimentation classes of molecules: 28-31 S, 22-24S, 18 S and 4-6 S. The 28-31 S molecules were not present among the RNAs of interfering particles of Lassa and Machupo viruses.
Subject(s)
Arenaviridae/genetics , Arenaviruses, New World/genetics , Lassa virus/genetics , RNA, Viral/analysis , Viral Interference , Animals , Arenaviruses, New World/physiology , Cell Line , Chlorocebus aethiops , Cricetinae , Lassa virus/physiology , Virion/analysis , Virion/genetics , Virus ReplicationABSTRACT
Sierra Leone strain of Lassa virus was growing to high titres of 10(5)-10(6) plaque forming units (PFU) per ml in Vero, L and swine kidney cell lines as well as in diploid human cells and primary human embryo kidney cells. As many as 80% of the cells became infected as demonstrated by the immunofluorescence (IF) technique. In BHK-21, CV-1, HeLa, FL, HEp-2 and dog kidney cell lines, the virus reproduced to lower titres (10(4)-10(5) PFU per ml), whereas in primary chick embryo fibroblasts it did not multiply at all. The virus formed plaques under agar overlay only in CV-1 and Vero cells.
