A. C. Chanas

Monoclonal antibodies to Sindbis virus glycoprotein E1 can neutralize, enhance infectivity, and independently inhibit haemagglutination or haemolysis.

Two monoclonal antibodies raised against Sindbis virus were shown to be specific for the envelope glycoprotein E1 by radioimmunoprecipitation (RIP). They had a number of contrasting biological properties. One of them was capable of neutralizing virus infectivity and inhibiting haemagglutination, while the other had no significant neutralizing or haemagglutination-inhibiting capability, but did inhibit virus-mediated haemolysis. Both monoclonal antibodies could enhance virus infectivity of Fc receptor-bearing macrophage-like cells when present at suitable dilutions.

Conformational changes in Sindbis virus E1 glycoprotein induced by monoclonal antibody binding.

A monoclonal antibody (30.2) raised against Sindbis virus is able to precipitate both E1 and PE2 from [35S]methionine-labelled infected cells solubilized with non-ionic detergent. Addition of SDS to the lysate abolishes the precipitation of PE2 without affecting that of E1, thus demonstrating that the antibody is specific for E1. Other Sindbis E1-specific monoclonal antibodies (30.11 and 30.12) precipitate only E1, even from lysates containing only non-ionic detergent, and their presence in such a lysate prevents precipitation of PE2 by antibody 30.2. These data indicate that E1-PE2 complexes stable in the presence of non-ionic detergent can be precipitated as such by one antibody, but that binding of the other antibodies induces dissociation of E1 and PE2. Competition experiments using 125I-labelled antibodies indicate that all three antibodies bind to distinct antigenic sites on the E1 molecule. Antibodies 30.11 and 30.12 stimulate each others binding in such experiments, which suggests that binding of either of these antibodies alters the conformation of E1 in such a way as to increase its affinity for the other, and at the same time to release PE2. Antibody 30.2 also enhances binding of the other two antibodies, but this stimulation is only weakly reciprocated.

Cross-neutralization study of seven California group (Bunyaviridae) strains in homoiothermous (PS) and poikilothermous (XTC-2) vertebrate cells.

Antigenic relationships among seven California group strains were studied by a plaque-reduction neutralization test (PRNT). Cross-reactions occurred in most cases but three subgroups were noted: (1) the major serogroup contained the viruses of California encephalitis, LaCrosse, Snowshoe Hare and Trahyna (including the Lumbo strain) whereas (2) Jamestown Canyon and (3) Trivittatus viruses were distinct. There was no significant difference between the PRNT results in mammalian (PS) cells incubated at 37 degrees C and amphibian (XTC-2) cells incubated at 28 degrees C. Trivittatus virus failed to produce plaques in XTC-2 cells.

Localization of An Arenavirus Protein in the Nuclei of Infected-Cells

Summary Host cell nuclear involvement in an arenavirus infection was examined by immunofluorescence. Both polyclonal antisera and monoclonal antibodies specific for the major nucleocapsid (N) polypeptide revealed virus-specific nuclear inclusions in Pichinde virus-infected Vero cells. Immunoprecipitation of infected cell extracts with the anti-N monoclonal antibodies and subsequent analysis by SDS-PAGE, identified two N-related proteins with mol. wt. of 36000 (p36) and 28000 (p28) in addition to the N polypeptide. Only those monoclonal antibodies which precipitated p28 as well as N and p36 were found to produce nuclear as well as cytoplasmic fluorescence. These findings suggest that either the p28 protein itself or a conformational variant of N was the nuclear antigen detected.

Evaluation of plaque size reduction as a method for the detection of Pichinde virus antibody.

SummaryThe reaction between Pichinde virus and homologous antisera has been studied using a plaque size reduction method. The incorporation of antiserum in the overlay of infected Vero cell monolayers revealed a pattern of virus-cell interactions which were manifested by both a significant reduction in the diameter of virus plaques, and regeneration of cells in the centre of each. Electron microscopy demonstrated that antibody molecules were bound to virus particles budding from the surface of infected cells resulting in the formation of extracellular virus-antibody complexes. These aggregates were subsequently detected in vacuoles of freshly-infected cells. In the absence of virus neutralization, reaction of Pichinde virus with homologous antiserum leads to the formation of infectious aggregates which due to their larger size restrict the rate of plaque development.

Arbovirus isolations from ixodid ticks infesting livestock, Kano Plain, Kenya

In a study conducted on the Kano Plain, Kenya, virus isolation attempts were made on ixodid ticks collected, over a 14-month period, from livestock held in family enclosures (bomas) before releasing the animals for daily foraging. 8735 Amblyomma variegatum (Fabricius) were tested, 98.6% of which were taken from cattle, yielding 36 strains of Dugbe (DUG), four strains of Nairobi sheep disease (NSD), three strains of Bhanja (BHA), one strain of Thogoto (THO) and five strains of virus which could not be characterized. 6549 Rhipicephalus spp. ticks were collected (60.3% from cattle). NSD, DUG and BHA viruses were each isolated twice from ticks taken from cattle. One BHA virus strain was recovered from ticks from a sheep. One strain recovered from ticks on cattle could not be characterized.

Immunofluorescence studies on the antigenic interrelationships of the Hughes virus serogroup (genus Nairovirus) and identification of a new strain.

Titrations of hyperimmune antisera by indirect immunofluorescence using each virus of the Hughes serogroup (Hughes, Zirqa, Punta Salinas, Soldado and Farallon) demonstrated their individual antigenic identities. Furthermore, an antigenically related virus, designated Puffin Island (PI) virus, was shown both by indirect immunofluorescence and by neutralization in XTC cells to be distinguishable from the other viruses. These viruses readily established persistent infections in Vero cells after producing only moderate cytopathic effects. Treatment of persistently infected cultures with either fluorodeoxyuridine or bromodeoxyuridine made no significant difference to the percentage of immunofluorescent cells. Attempts to demonstrate haemagglutination by Zirqa virus were unsuccessful.

Localization of arenavirus proteins in the nuclei of infected cells

Host cell nuclear involvement in an arenavirus infection was examined by immunofluorescence. Both polyclonal antisera and monoclonal antibodies specific for the major nucleocapsid (N) polypeptide revealed virus-specific nuclear inclusions in Pichinde virus-infected Vero cells. Immunoprecipitation of infected cell extracts with the anti-N monoclonal antibodies and subsequent analysis by SDS-PAGE, identified two N-related proteins with mol. wt. of 36,000 (p36) and 28,000 (p28) in addition to the N polypeptide. Only those monoclonal antibodies which precipitated p28 as well as N and p36 were found to produce nuclear as well as cytoplasmic fluorescence. These findings suggest that either the p28 protein itself or a conformational variant of N was the nuclear antigen detected.