N. Hashimoto

Protective role of antigenic sites on the envelope protein of Hantaan virus defined by monoclonal antibodies

SummaryTo investigate the role of Hantaan virus envelope glycoprotein in infection, a panel of monoclonal antibodies (MAbs) was examined in vitro with several serological tests and in vivo by passive transfer experiments in mice. An antigenic site, specific for the inhibition of infected cell focus was detected with the focus inhibition neutralization test (FINT), in addition to the neutralization related antigenic sites, which were revealed by the ordinary focus reduction neutralization test (FRNT). Suckling mice were given the MAbs by passive transfer followed by lethal Hantaan virus challenge. All neutralizing MAbs detected by either FRNT or FINT protected all mice from lethal infection, confirming the importance of the antigenic sites as a protective antigen. Mice given non-neutralizing MAbs by passive transfer, however, began to die earlier than the control group; mean time to death (18.2±2.1 to 21.5±2.8 days) being significantly shorter than that of the control group (25.8±1.8, p<0.01, Mann-Whitney,U probability test). Virus titers in brains of mice which died early, were about 10 times higher than those of control mice. These results indicated the early death phenomenon of mice which was mediated by the antivirus antibody.

Cell fusion by haemorrhagic fever with renal syndrome (HFRS) viruses and its application for titration of virus infectivity and neutralizing antibody

SummaryHaemorrhagic fever with renal syndrome viruses, are members of the family Bunyaviridae. They cause cell to cell fusion from within under acidic conditions. This phenomenon was found to occur under a pH range of between 4.9 to 6.3 for all the viruses examined. The pH range which causes cell fusion was similar to that reported for the La Crosse virus of the Bunyaviridae, hence indicating that this property is a common biological characteristic among this family of viruses.Titration of virus infectivity and neutralizing antibody was done by counting the number of fused cell foci produced in infected Vero cell monolayers after low pH treatment. This method was simpler and more rapid than the ordinary plaque formation method or that of counting infected cell foci by IFA or immunoenzyme assay. In addition, this method may also be applicable in the detection of other enveloped viruses which do not cause a typical cytopathic effect.

Modes of Seoul virus infections : persistency in newborn rats and transiency in adult rats

SummaryTo understand the mode of persistent infection of Seoul virus in rodents, we examined the distribution of the virus genome and antibody production in infected rats. When 1-day-old rats were inoculated with the KI-83-262 strain, the S segment of viral genome was detected in sera, clots, lungs and kidneys from 3 to 184 days post inoculation (d.p.i.) by nested reverse transcriptase PCR. On the other hand, when 7-week-old rats were infected with this virus, viral genome was detected only in the lungs from 3 to 50 d.p.i. The neutralizing antibody titers of rats inoculated at 1-day of age were higher than those of rats inoculated at 7 weeks of age. In both age groups, however, the IgG avidity of antibody increased along with the course of infection. We found that urban rats (Rattus norvegicus) infected early in life harbored the virus for more than 6 months.

Role of maternal antibody in protection from hemorrhagic fever with renal syndrome virus infection in rats

SummaryThe effect of maternal antibody on the protection of newborn rats from infection by HFRS virus strain SR-11 was examined. Antibody to HFRS virus was transferred from immune dams to their offspring prenatally as well as postnatally. IgG antibody was detected in the sera of fetuses by IFA test (titers from 1:64 to 1:256) and in fetal fluids (1:32) obtained from the uteri of immune dams at 20 days after mating. In the sera of the newborn, IgG titers of maternal antibody ranged from 1:64 to 1:256 just after birth, reached a peak titer around 1:2,048 at 2 weeks after birth, then declined and disappeared at about 8 weeks of age. No IgA and IgM antibodies were detected in the sera of fetuses and newborns. After intraperitoneal challenge by strain SR-11 (102.2 LD50), death and infection of 2-day-old rats from immune dams were prevented by the presence of maternal antibody. The protective effect of maternal antibody remained in 8-week-old rats having an IFA titer of maternal antibody as low as 1:16, and even in some 10-week-old rats with negative tests for maternal antibody.

Urine-associated horizontal transmission of Seoul virus among rats

SummaryTo understand the mode of transmission of Seoul type hantavirus in Wistar rats, we examined the shedding of the virus and antibody production in infected rats. When 1-day-old rats were inoculated with the KI-83-262 strain of Seoul virus, S segment of the viral genome was detected in lungs, clots, urine, saliva, submaxillary glands, rectums, and kidneys by nested reverse transcriptase PCR. On the other hand, when 8-week-old rats were infected with the virus, viral genome was detected only in the lungs and rectum. In newborn rats intranasally administered urine from infected newborn rats, four of six rats shed the virus into their urine. In addition, three of eight rats kept in the same cage with infected animals also shed the virus into urine. Moreover, the virus genome was detected in the urine of urban rats (Rattus norvegicus) in an enzootic focus. These findings suggest that the urine containing virus from infected † rats is an actual source of the Seoul virus infection.

Epidemiological studies of hemorrhagic fever with renal syndrome (HFRS) related virus infection among urban rats in Hokkaido, Japan

SummarySeroepidemiological studies of hemorrhagic fever with renal syndrome (HFRS) virus infection were carried out among urban rats(Rattus norvegicus andRattus rattus) and small field rodents in Hokkaido, Japan. An urban rat colony that was seropositive to SR-11 strain of HFRS virus (laboratory rat origin) was demonstrated in February 1983 at a dumping ground area of Kami-iso Town near Hakodate port. An HFRS-related virus, named KI-262 strain, was isolated from the lung tissue of a seropositive rat using Vero-E6 cell culture. Antigenicity of the isolate was closely related to Hantaan 76–118 and SR-11 strains by the indirect immunofluorescent antibody (IFA) test. No seropositive rat was found among the 861 rats captured in 38 other regions. It is unclear whether or not the infected rats in the positive area were introduced from abroad, though the area is located near Hakodate International Port. Furthermore, higher positive rates of urban rats in the Kami-iso area were observed in the spring and winter than in the summer and fall. Significantly high proportion of positive cases was observed among adult rats (six months or older) than among younger animals. The seasonal and age distribution of postive cases suggested that the virus was not readily transmitted from one infected rat to another. One seropostive case of a small field mouse(Clethrionomys rufocanus bedfordiae) was detected around the Kami-iso area.

Antibody-dependent enhancement of hantavirus infection in macrophage cell lines

SummaryAntibody-dependent enhancement (ADE) of hantavirus infections (strains Hantaan 76–118 and SR-11) was studied using macrophage-like cell lines (J774.1, P388D1, and U937). Significantly higher virus titers (1,000 to 4,000 FFU/ml) were obtained by pretreatment of the virus with immune serum as compared to normal serum (<20 FFU/ml). Monoclonal antibodies (MAbs) to strain Hantaan 76–118 were employed to determine the antigenic determinants responsible for the ADE activity. ADE of the infection occurred with MAbs to both G1 and G2 envelope glycoproteins, but not with MAbs to nucleocapsid protein. Antigenic determinants related to haemagglutination or virus neutralization were found to cause ADE of the infection.

Getah virus inAedes vexans nipponii andCulex tritaeniorhynchus: Vector susceptibility and ability to transmit

SummaryVector competences ofAedes (Ae.) vexans nipponii (nip.) andCulex (Cx.) tritaeniorhynchus to Getah virus were assessed by using a membrane feeding technique. The Getah virus was present at high titer in both species of mosquitoes after 21 days of extrinsic incubation at 28° C. Infection rates on 21 post-feeding were 100 per cent (4/4) forAe. vexans nip. at a virus dosage of 105.3 PFU/ml and 60 per cent (3/5) forCx. tritaeniorhynchus at similar virus dosage. More than 103.5 PFU of virus was detected in salivary glands of both species of mosquitoes on day 21 of extrinsic incubation. Forty percent (2/5) ofAe. vexans nip. transmitted the virus into serum-agar after ingesting 104.3 PFU/ml of virus blood mixture. In experiments withCx. tritaeniorhynchus ingesting 107.5 PFU/ml of virus blood mixture, 57 per cent (4/7) were able to transmit the virus to suckling mice and 59 per cent (10/17) transmitted the virus into serum-agar.