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SUMMARYThe antigenic characteristics of eight human strains and two bovine strains, one of which is represented by two plaque variants, of parainfluenza virus type 3 were analysed. The strains and variants were compared using 52 monoclonal antibodies against five, two, six and six epitopes of the haemagglutinin neuraminidase (HN), fusion, nucleocapsid and matrix viral proteins respectively, employing radioimmunoprecipitation and immunofluorescence assays. The human strains, seven of which were isolated over 6 years at different geographical locations and the eighth one representing an older prototype strain, showed very little antigenic variation. Extensive differences were detected in all four proteins examined between the human strains and the two strains of bovine origin. Two bovine variants were less effectively neutralized than the prototype human strain with a series of monoclonal antibodies against the HN protein.

SUMMARYMonoclonal antibodies directed against four structural components of the ATCC strain C243 of parainftuenza virus type 3 were produced. The specific reaction of the antibodies with individual structural components was determined by radioimmune precipitation assay. In the collection of monoclonal antibodies, 21 reacted with the haemagglutinin-neuraminidase (HN) glycoprotein (mol. wt. 72000), eight with the fusion (F) glycoprotein (mol. wt. 64000), 27 with the nucleocapsid (NP) protein (mol. wt. 69000) and 24 with the matrix (M) protein (tool. wt. 40000). The F-specific monoclonal antibodies precipitated two proteins which were interpreted to represent intact F protein and the large cleavage product F1 (mol. wt. 52000). The numbers of epitopes were determined in a competition ELISA with the monoclonal antibodies. The epitopes found were six for the HN, two for the F, six for the NP and six for the M protein. The six groups of antibodies reacting with different epitopes on the HN molecule showed varying capacities to inhibit biological activities. Two exhibited high neutralization (NT), haemagglutination inhibition (HI) and haemolysis inhibition (HLI) activity. Three groups had somewhat lower NT, lower HI and no detectable HLI activity. One group showed no activity in these tests. Of the eight monoclonal antibodies directed to the F protein two had demonstrable HLI activity.

SUMMARYAntigenic characteristics of nine mumps virus strains were determined by immunofluorescence and radioimmunoprecipitation assay (RIPA) using a collection of 44 monoclonal antibodies. These antibodies were directed against five different structural components of mumps virus, the haemagglutinin-neuraminidase (HN), fusion (F), matrix (M), phospho-(P) and nucleocapsid (NP) proteins. The nine mumps virus strains could be divided into two groups according to their antigenic characteristics. One group included two strains isolated more than a decade ago and the Jeryl Lynn vaccine strain. These three strains reacted with a wider range of monoclonal antibodies than the second group of six recently isolated strains of different geographical origin. In the F, M and P proteins variations were only found in single antigenic determinants. In the HN and NP components, RIPA revealed variations in three and seven determinants respectively. The Jeryl Lynn vaccine strain showed a unique lack of reaction with one anti-HN antibody clone in the RIPA.

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With the aid of monoclonal antibodies directed against a specific site on the hemagglutinin-neuraminidase surface glycoprotein, four mutants of the Kilham neurotropic strain of mumps virus were isolated. All four mutants had increased neuraminidase activity. Two mutants (M1O and M12) lost their hemagglutination capacity with human 0 erythrocytes but retained their ability to agglutinate guinea pig erythrocytes at 40C. A third mutant (Mll) showed a change in the molecular weight of the hernagglutinin-neuraminidase glycoprotein. These three mutants (M10, Mll, and M12) showed unaltered capacity to infect tissue cultures and to cause encephalitis in newborn hamsters. A fourth mutant (M13) retained its hemagglutination activity and capacity to infect Vero cell cultures but showed significantly lower neurovirulence in the suckling hamster brain than did the parental Kilham strain and the other three mutants. Both the number of infected neurons and the amount of infectious virus in the brain was reduced. On the other hand, there were no apparent differences in the occurrence of viral antigen in ependymal cells, indicating a selective change in affinity for neurons in the brain. These results suggest that certain changes in the hemagglutinin-neuraminidase glycoprotein may lead to an alteration of the neuropathogenicity of the Kilham strain of mumps virus.

A monoclonal antibody against the fusion (F) protein of mumps virus was found to confer nmarked protection in mumps virus-induced encephalitis. Almost total prevention of extensive brain necrosis was found. This study indicates that the virus F protein is directly involved in the pathogenesis of brain necrosis. Monoclonal antibodies to specific antigenic sites on viral

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