Lassa and Mopeia virus replication in human monocytes/macrophages and in endothelial cells: different effects on IL-8 and TNF-alpha gene expression.
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. (+info)
Characterization of human CD4(+) T-cell clones recognizing conserved and variable epitopes of the Lassa virus nucleoprotein.
T cells must play the major role in controlling acute human Lassa virus infection, because patients recover from acute Lassa fever in the absence of a measurable neutralizing antibody response. T cells alone seem to protect animals from a lethal Lassa virus challenge, because after experimental vaccination no neutralizing antibodies are detectable. In order to study human T-cell reactivity to single Lassa virus proteins, the nucleoprotein (NP) of Lassa virus, strain Josiah, was cloned, expressed in Escherichia coli, and affinity purified. Peripheral blood mononuclear cells (PBMC) obtained from 8 of 13 healthy, Lassa virus antibody-positive individuals living in the Republic of Guinea, western Africa, were found to proliferate in response to the recombinant protein (proliferation index >/=10). PBMC obtained from one individual with a particularly high proliferative response were used to generate 50 NP-specific T-cell clones (TCC). For six of these the epitopes were mapped with overlapping synthetic peptides derived from the sequence of the NP. These CD4(+) TCC displayed high specific proliferation and produced mainly gamma interferon upon stimulation with NP. Because variation of up to 15% in the amino acid sequences of the structural proteins of naturally occurring Lassa virus variants has been observed, the reactivity of the TCC with peptides derived from the homologous epitopes of the Nigeria strain of Lassa virus and of the eastern Africa arenavirus Mopeia was tested. With the Nigeria strain of Lassa virus the levels of homology were 100% for two of these epitopes and 85% for three of them, whereas homology with the respective Mopeia epitopes ranged from 92 to 69%. Reactivity of the TCC with peptides derived from the variable epitopes of the Nigeria strain and of Mopeia was reduced or completely abolished. This report shows for the first time that seropositive individuals from areas of endemicity have very strong memory CD4(+) T-cell responses against the NP of Lassa virus, which are partly strain specific and partly cross-reactive with other Lassa virus strains. Our findings may have important implications for the strategy of designing recombinant vaccines against this mainly T-cell-controlled human arenavirus infection. (+info)
The pathology of human Lassa fever.
Pathological findings have been described in only a small number of cases of Lassa fever since the virus was first isolated in 1969. Morphologically, eosinophilic necrosis of hepatocytes was the most frequent finding and focal necroses, often extensive, were present in most cases. These findings are similar to the lesions previously described in Argentinian and Bolivian haemorrhagic fever. Focal interstitial pneumonitis, focal tubular necrosis in the kidney, lymphocytic infiltration of the splenic veins, and partial replacement of the splenic follicles by amorphous eosinophilic material have been described, but the significance of these findings is unclear. More detailed and sophisticated investigations are required in the future if pathogenetic mechanisms are to be unravelled. (+info)
Surveillance of Lassa fever in missionaries stationed in West Africa.
To determine the distribution of Lassa virus in West Africa, a serological survey was undertaken. A number of mission hospital supplied sera from patients admitted with a history of fever and specimens were also collected in New York from missionaries who had experienced an unusual febrile illness while working in Africa. More cases of Lassa fever were detected among missionaries than among Africans, possibly because many African patients had left hospital before the complement fixation tests had become positive. Although most adults had fairly high fever and some were prostrated, fever was less severe in the children examined. In general the findings confirm that not all Lassa fever patients have the severe syndrome described in the original reports. (+info)
Lassa fever in Onitsha, East Central State, Nigeria in 1974.
Three cases of Lassa fever occurred in Onitsha, East Central State, Nigeria, in January and February 1974. The first case was a 19-year-old Nigerian; the other 2 cases were German missionary physicians at St Charles Borromeo Hospital, Onitsha, one of whom cared for the patient who was the first case. Thus, 2 of the 3 cases were hospital acquired. Investigations failed to discover a village outbreak or the source of virus for the first case. A serosurvey of 258 hospital staff members and contacts of the 3 cases showed no other persons with antibody to Lassa virus. The absence of Lassa virus antibody in a high-risk group indicates a low or nonexistent level of past Lassa virus activity in southeastern Nigeria. (+info)
Use of the complement fixation (CF) test in Lassa fever surveillance. Evidence for persistent CF antibodies.
A survey to detect individuals with antibodies to Lassa virus was undertaken among hospital personnel in the eastern and southern provinces of Sierra Leone late in 1974. Sera were evaluated by the complement fixation test. The data obtained showed that some contacts of Lassa fever patients in the 1972 epidemic had developed antibodies to the virus; individuals who had never reported being sick also showed evidence of infection, with significant CF antibody titres in their sera. Surviving Lassa fever patients from the 1972 epidemic still had easily measurable levels of persisting CF antibodies. The significance of these data is discussed; in addition it is recommended that the CF test should continue to be the method of choice in mass surveys for this virus disease until other tests can be developed. (+info)
Recent isolations of Lassa virus from Nigerian rodents.
Rodents were trapped in the Benue-Plateau and North-Eastern States of Nigeria where Lassa fever had been reported in previous years. Eight Lassa virus strains were isolated from tissues and blood of rodents identified in the field as being of 3 different species: Mastomys natalensis, Rattus rattus, and Mus minutoides. All the infected rodents were collected in village habitats. These isolations indicate the presence of Lassa virus in wild rodents in Nigeria during periods when no human infections were evident.Prior studies in Sierra Leone have indicated that a single rodent species, M. natalensis, may be the important reservoir host of Lassa virus. Since the present study indicates that other rodent species may be involved as well, the ecology of Lassa virus may be more complicated than was heretofore supposed. In view of the importance of determining the geographic and species range of rodent hosts of Lassa virus, and because of the problems inherent in rodent identification under austere field conditions, it is urgent that further studies be conducted in the same areas of Nigeria to confirm these findings. (+info)
Lassa virus infection in Mastomys natalensis in Sierra Leone. Gross and microscopic findings in infected and uninfected animals.
Pathological examinations of 28 wild-caught Mastomys natalensis from Sierra Leone, 14 of which were positive for Lassa virus by tissue culture, are reported. The high frequency of neoplastic and degenerative diseases observed among older animals in closed colonies of M. natalensis were not observed in the wild animals studied. This is probably a reflection of the age distribution of the study population, since the life expectancy of wild Mastomys is less than a year. Inflammatory lesions were nonetheless identified, some of which were similar to those described in laboratory colonies. Frequent lesions were myocarditis (54%), myositis (32%), interstitial pneumonitis (50%), intercapillary glomerulosclerosis (36%), and acute nephrosis (14%). Follicular and nodular lymphoid hyperplasia were evident in the spleen (74%) and Peyer's patches (64%). Lymphoid cell accumulations were prominent in the salivary glands (36%), periportal hepatic region (25%), lungs (32%), perivascular regions (36%), and kidney (21%). Cytomegalic inclusion body sialoadenitis was common (25%). Coccidiosis was evident in the intestinal tract (25%), kidney (25%), and muscle (21%). One neoplasm, a parahepatic haemangioma, was observed histologically.Mean body weights and lengths for virus-positive animals (33 g and 9.2 cm) and virus-negative animals (54 g and 12.2 cm) showed that virus-positive animals were smaller in weight and shorter in length. Since the age of the animals could not be determined, these differences remain unexplained.In comparison with virus-negative animals, virus-positive Mastomys had higher frequencies of splenic follicular hyperplasia (82% against 50%), myocarditis (79% against 29%), perivascular lymphoid cell accumulation (57% against 7%), myositis (50% against 14%), and cytomegalic inclusion body sialoadenitis (36% against 14%). The frequency of lymphoid hyperplasia of Peyer's patches was high in both groups of animals (71% and 57%).The presence of Lassa virus, small size, myocarditis, and lymphoid perivasculitis appeared to be interrelated, but larger and better controlled studies are required to elucidate the relationship. (+info)