New viral infections of humans appear to be emerging at an increasing tempo, probably due to technological developments and societal changes that have enhanced the ability of viruses to invade and spread within the human population. Emergence can be due to several discrete phenomena. Existing viruses of humans continue to be isolated, identified, followed by the description of new nosological entities. An increase in the ratio of cases:infections for ubiquitous viruses may lead to the emergence of new epidemics, associated either with the altered host susceptibility or increased viral virulence. Finally, viruses may invade populations from which they have disappeared or may cross the species barrier to invade new species. When a virus invades a new species it usually fails to spread from individual to individual. However, on rare occasions a virus adapts to a new species, usually involving mutations in the viral genome that alter the cellular host range. In such instances, if circumstances favor transmission, a pandemic may occur. For a new virus to endanger blood products, several criteria must be met. First the virus must be able to spread widely in the human population; second, it must cause a persistent plasma viraemia of moderate to high titre (although there are exceptions); and third, virus carriers must be asymptomatic. This set of conditions has only occurred once in the recorded history of human virology, with human immunodeficiency virus. It would probably be difficult to predict another invasion of the human population with a new virus, at least from studies in comparative virology. Probably the best deterrent strategy to facilitate the early recognition of any such hypothetical rare occurrence is the identification and control of all viruses that presently endanger the blood supply, supplemented by an active surveillance system to identify post-transfusion illnesses of any kind.

The California serogroup is composed of antigenically and biologically related viruses within theBunyavirusgenus of the Bunyaviridae. We used a large panel of murine cells to study their tissue tropisms and found virtually identical patterns of viral replication among all of the members of this serogroup, in contrast to other members of the family (Bunyamwera, Cache Valley, and Punta Toro viruses). By analyzing the nonpermissive infections with both an RNA dot-blot and a virus binding assay, we determined that tropism for cultured cells was determined at the level of entry. A truncated soluble form of the La Crosse G1 glycoprotein (sG1) was expressed in a baculovirus system and, despite slight differences in glycosylation, was shown to resemble native G1 by immunoprecipitation with six monoclonal antibodies. sG1 bound to permissive but not to nonpermissive cell lines, as demonstrated by flow cytometry. The sG1 effectively blocked infection of permissive cell lines with all of the California serogroup viruses, but did not block infection of two other bunyaviruses. These results indicate that the California serogroup bunyaviruses share a common receptor on vertebrate cells which may differ from the receptor used by other Bunyaviridae and demonstrate that the G1 glycoprotein is the virus attachment protein. sG1 will be a useful reagent in the search for a putative receptor molecule.

La Crosse virus, a member of the California serogroup of bunyaviruses, is an important cause of pediatric encephalitis in the midwestern United States. Like all bunyaviruses, La Crosse virus contains two glycoproteins, G1 and G2, the larger of which, G1, is the target of neutralizing antibodies. To develop an understanding of the role of each of the glycoproteins in the generation of a protective immune response, we immunized 1-week-old mice with three different preparations: a vaccinia virus recombinant (VV.ORF) that expresses both G1 and G2, a vaccinia virus recombinant (VV.G1) that expresses G1 only, and a truncated soluble G1 (sG1) protein prepared in a baculovirus system. Whereas VV.ORF generated a protective response that was mostly directed against G1, VV.G1 was only partially effective at inducing a neutralizing response and at protecting mice from a potentially lethal challenge with La Crosse virus. Nevertheless, a single immunization with the sG1 preparation resulted in a robust immune response and protection against La Crosse virus. These results indicate that (i) the G1 protein by itself can induce an immune response sufficient for protection from a lethal challenge with La Crosse virus, (ii) a neutralizing humoral response correlates with protection, and (iii) the context in which G1 is presented affects its immunogenicity. The key step in the defense against central nervous system infection appeared to be interruption of a transient viremia that occurred just after La Crosse virus inoculation.

To characterize the role of the placenta in vertical transmission of human immunodeficiency virus type 1 (HIV-1), the susceptibility of primary human placental cultures and of transformed trophoblast cell lines to infection by several HIV-1 isolates was examined. Placental cultures supported the replication of all strains tested, including lymphocyte-, macrophage-, and amphotropic isolates. All viruses replicated to modest levels, with production of both viral antigen and infectious virus in the culture supernatants. Placental cells demonstrated a pattern of permissiveness for HIV-1 isolates distinct from that seen with lymphocytes, blood-derived macrophages, or T cell lines. Immunofluorescent staining showed that 5%-10% of the cultured placental cells expressed viral antigens, and double labeling revealed that the HIV-positive cells were macrophages not trophoblasts. None of the trophoblast cell lines (JEG-3, Jar, BeWo, HP-W1) could be infected by HIV. These results support the hypothesis that infection of the placenta could play a role in maternofetal transmission of HIV-1 and suggest that the placental macrophage is likely to be the primary cell type responsible.

Annals of the New York Academy of SciencesVolume 724, Issue 1 p. 87-106 Pathogenesis of HIV Encephalopathya NEAL NATHANSON, NEAL NATHANSON Departments of Microbiology and Neurology University of Pennsylvania Medical Center Philadelphia, Pennsylvania 19104-6076Search for more papers by this authorDAVID G. COOK, DAVID G. COOK Departments of Microbiology and Neurology University of Pennsylvania Medical Center Philadelphia, Pennsylvania 19104-6076Search for more papers by this authorDENNIS L. KOLSON, DENNIS L. KOLSON Departments of Microbiology and Neurology University of Pennsylvania Medical Center Philadelphia, Pennsylvania 19104-6076Search for more papers by this authorFRANCISCO GONZALEZ-SCARANO, FRANCISCO GONZALEZ-SCARANO Departments of Microbiology and Neurology University of Pennsylvania Medical Center Philadelphia, Pennsylvania 19104-6076Search for more papers by this author NEAL NATHANSON, NEAL NATHANSON Departments of Microbiology and Neurology University of Pennsylvania Medical Center Philadelphia, Pennsylvania 19104-6076Search for more papers by this authorDAVID G. COOK, DAVID G. COOK Departments of Microbiology and Neurology University of Pennsylvania Medical Center Philadelphia, Pennsylvania 19104-6076Search for more papers by this authorDENNIS L. KOLSON, DENNIS L. KOLSON Departments of Microbiology and Neurology University of Pennsylvania Medical Center Philadelphia, Pennsylvania 19104-6076Search for more papers by this authorFRANCISCO GONZALEZ-SCARANO, FRANCISCO GONZALEZ-SCARANO Departments of Microbiology and Neurology University of Pennsylvania Medical Center Philadelphia, Pennsylvania 19104-6076Search for more papers by this author First published: May 1994 https://doi.org/10.1111/j.1749-6632.1994.tb38898.xCitations: 13 a Supported in part by USPHS grants NS 27405, NS 30606, NS 21067, and NS 01581. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume724, Issue1Slow Infections of the Central Nervous System: The Legacy of Dr. Björn SigurdssonMay 1994Pages 87-106 RelatedInformation

The neuroinvasiveness of California serogroup bunyaviruses is determined by the ability of the virus to replicate in striated muscle after peripheral inoculation of mice. Neuroinvasiveness was mapped to the medium (M) RNA segment of the virus, which encodes the viral glycoproteins, when reassortants were made between La Crosse/original virus, a neuroinvasive isolate, and Tahyna-181/57 virus, a nonneuroinvasive clone. We have tested the murine muscle cell line C2C12 as a surrogate for myotropism and have found that there is a slight, but reproducible difference in the replication of virus clones bearing the M RNA segment of La Crosse/original virus compared to clones bearing the M RNA segment of Tahyna-181/57 virus, as determined by viral titer, antigen expression, and plaque formation.

California bunyaviruses cause encephalitis in mammalian hosts after peripheral infection. The virulence of these viruses is determined by their ability to replicate sequentially in striated muscle, cause viremia, and invade and replicate in the central nervous system. These viruses are also able to infect vector mosquitoes following ingestion of a blood meal containing virus. Bunyaviruses are negative stranded RNA viruses with a trisegmented genome, and the large, medium, and small RNA segments encode the polymerase, the glycoproteins, and the nucleoprotein, respectively. Reassortants between virulent and avirulent virus clones have been used to map virulence determinants in mice as well as determinants of infectivity in mosquitoes. Attenuation in mice and infectivity in mosquitoes of some virus clones maps to the medium RNA segment, implying that the virus glycoproteins, which are involved in virus entry, play a role in virulence. Attenuation in mice and mosquito infectivity of other clones maps to the large RNA segment, suggesting that cell-specific differences in the function of the viral polymerase can also determine virulence and host range.

The gastrointestinal tract plays a major role in the pathogenesis and pathophysiology of infection by the type 1 human immunodeficiency virus (HIV-1). It is a potential route for viral entry and it is the site of a number of complications, including both opportunistic infections and a primary HIV-induced enteropathy. Correspondingly, both in vivo and in vitro studies have demonstrated HIV infection of gastrointestinal cells of lymphoid and epithelial origin. HT-29, a human colonic epithelial cell line that is infectable with many HIV-1 strains, does not express CD4 protein or mRNA. Recent studies showed that antibodies recognizing a neutral glycolipid related to galactosylceramide (GalCer) in HT-29 cells inhibited HIV-1 infection of this cell line, extending previous findings in neural cells. In the current studies, we further analyzed the neutral glycolipids of HT-29 cells and showed that they contained authentic GalCer and that recombinant gp120 bound to this glycolipid. Moreover, by analyzing GalCer expression in clones derived from HT-29 and Caco-2 (another human colonic cell line), we observed that the level of expression of this glycolipid was associated with the sensitivity to HIV-1 infection. Subclones of Caco-2 did not express GalCer and were not infectable with any of three HIV-1 strains. These results strengthen the possibility that GalCer is an alternative receptor in CD4- cell lines. Furthermore, since GalCer is a major glycolipid in epithelial cells of the small intestine and colon, these results provide a structural basis for the binding of HIV-1 by gastrointestinal epithelial cells and the entry of the virus into those cells.

A method is described for the production and assay of pseudotype viruses between human immunodeficiency virus type 1 (HIV-1) and Cocal virus (COV), containing an HIV-1 envelope and a COV genome (COV(HIV)). COV(HIV) pseudotype virus is a useful tool for the investigation of a variety of questions regarding HIV entry into susceptible cells, including steps in virus binding, fusion, and internalization, and the role of molecules which inhibit entry. COV, a rhabdovirus closely related to vesicular stomatitis virus (VSV), replicated and caused cytopathic effect in primary cultures of human peripheral blood lymphocytes (PBLs) and monocyte-derived macrophages (MDM), and in human cell lines of lymphocytoid or monocytoid origin, making it an ideal candidate for pseudotype production. 174XCEM cells, which were permissive for selected macrophage-tropic strains as well as most lymphocyte-tropic strains of HIV-1, were used to produce stocks of putative pseudotype virus. To neutralize parental COV in these stocks, a rabbit antiserum was produced which had a neutralization index of > 10(7) at a dilution of 1:100. Using these methods, pseudotype viruses were produced with a titer of about 10(4) PFU per ml; these same stocks contained HIV-1 at a titer of about 10(5) TCD50 per ml and COV at a titer of about 10(8) PFU per ml. CD4-expressing HeLa cells were used to assay pseudotype stocks made with lymphocyte-tropic strains of HIV-1. The authenticity of the pseudotype stocks was validated by several controls, including their failure to register on congenic CD4-negative HeLa cells and their inhibition by monoclonal anti-CD4 antibodies such as Leu 3a.

To investigate the mechanism underlying one aspect of the cellular tropism of human immunodeficiency virus type 1 (HIV-1), we used a macrophage-tropic isolate, 89.6, and screened its ability to infect a number of continuous cell lines. HIV-1 (89.6) was able to replicate robustly in a T-cell/B-cell hybrid line, CEMx174, while it replicated modestly or not at all in either of its parents, one of which is the CD4-positive line CEM.3. Analysis by transfection of a molecular clone, a virus uptake assay, and polymerase chain reaction all provided strong evidence that the block to HIV-1(89.6) replication in the CEM.3 line lies at the level of cellular entry. These results were complemented by preparing a CD4-expressing derivative of the B-cell parent, 721.174, and demonstrating that it is permissive for productive HIV-1(89.6) replication. Given these experimental findings, we speculate that there exist cellular accessory factors which facilitate virus entry and infection in CD4-positive cells. Furthermore, these cellular accessory factors may be quite virus strain specific, since not all macrophage-tropic strains of HIV-1 were able to replicate in the CEMx174 hybrid cell line. This experimental model provides a system for the identification of one or more of these putative cellular accessory factors.

The pathogenesis of the California serogroup bunyaviruses includes both extraneural and intraneural replicative phases that can be separated experimentally. The present study dissects the viral genetic determinants of extraneural replication. We have previously described two attenuated reassortant clones of California serogroup bunyaviruses which exhibit reduced neuroinvasiveness after subcutaneous inoculation into suckling mice. Clone B1-1a bears an attenuated middle RNA segment (neuroinvasiveness phenotype v alpha v), and clone B.5 bears an attenuated large RNA segment (neuroinvasiveness phenotype alpha vv). We prepared reassortant viruses between these two strains and found that the two attenuated gene segments acted independently and additively, since reassortants bearing two attenuated RNA segments were more attenuated than the parental clones. Reassortants bearing no attenuated RNA segments were much more neuroinvasive than either parental clone, indicating that a neuroinvasive strain can be derived from two attenuated clones. Pathogenesis studies demonstrated that after injection of 10(3) PFU, the attenuated reassortant clones did not replicate in peripheral tissue, failed to reach the brain, and did not cause disease. At a dose of 10(6) PFU, attenuated clones failed to replicate to a significant level in peripheral tissue and produced only a minimal passive plasma viremia during the first 24 h but nevertheless reached high titers in the brain and killed mice. Because of this result, we investigated the possibility that neuroinvasion occurs via retrograde axonal transport, by determining whether sciatic nerve sectioning could protect against virus infection after hind leg footpad inoculation. We found that nerve sectioning had no effect on lethality, ruling out this mode of entry and suggesting that passive viremia is likely to be sufficient for invasion of the central nervous system.

Oral poliovirus vaccine (OPV) is tested for safety by evaluation of neurovirulence in rhesus and cynomolgus macaques. After intraspinal or intrathalamic injection of varying doses of vaccine, monkeys are followed for 17-21 days, killed, and a histopathological evaluation is made of the severity of poliomyelitis lesions in the spinal cord and brainstem. Each production lot of vaccine is compared with a type 1 OPV reference virus tested by the same method. Records of neurovirulence tests on production lots of type 3 OPV manufactured by Lederle Laboratories, during the period 1964-1988, have recently become available, together with the corresponding tests on type 1 reference vaccine. The cumulative data were collated, using a system under which each monkey was given a single grade according to the severity and spread of neuropathological poliomyelitis lesions. These raw data were assembled into frequency distributions ('neurovirulence profiles'), and used to compare type 3 OPV with the reference vaccine. These comparisons included monkeys injected by intraspinal injection (three vaccine dose levels) and intrathalamic injection (one vaccine dose level), and comprised independent tests conducted by the Food and Drug Administration and by the vaccine manufacturer. A total of 13 different comparisons were made, each one consisting of a pair of profiles, on type 3 OPV and reference vaccine, respectively. In total, these comparisons represented tests on more than 12,000 monkeys. Based on these neurovirulence profiles, the type 3 OPV appeared to be no more virulent than the reference vaccine.(ABSTRACT TRUNCATED AT 250 WORDS)

We isolated and molecularly cloned a human immunodeficiency virus type 1 (HIV-1) strain (89.6) which is unusual because it is both macrophage-tropic and extremely cytopathic in lymphocytes. Moreover, this is the first well-characterized infectious molecularly cloned macrophage-tropic HIV-1 strain derived from peripheral blood. HIV-1 89.6 differs markedly from other macrophage-tropic isolates within the envelope V3 region, which is important in determining cell tropism and cytopathicity. HIV-1 89.6 may thus represent a transitional isolate between noncytopathic macrophage-tropic viruses and cytopathic lymphocyte-tropic viruses.