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The hemadsorption (HAD) reaction of chick embryo cells infected with mumps virus was studied by means of light and electron microscopy, with special reference to the plasma membrane of the infected cell. The concomitant observation of membrane-free aggregates of viral nucleocapsid in the cytoplasm and attached red blood cells on the surface of the same cell indicated that only infected cells hemadsorbed and that hemagglutinin is confined within the infected cell. The attachment of red blood cells to morphologically intact cell membrane prior to its differentiation into viral envelope suggested that the HAD phenomenon, dependent on the presence of hemagglutinin, was independent of the viral maturation process. The gap of low electron density normally separating the morphologically intact membrane of the tissue culture cell and that of the red blood cell at the binding site was replaced by newly formed surface projections in HAD involving a segment of differentiated plasma membrane.

The fine structure of mumps virus-infected chick embryo fibroblastic cells was examined sequentially after viral inoculation. Intracytoplasmic nucleoprotein strands, similar to those described for parainfluenza viruses, were detectable in small aggregates between 36 and 48 hr. The peripheral strands of this viral component lie beneath and along an antigenically altered bulging portion of the cell membrane. The outermost strands are consistently parallel to the differentiated segment of the plasma membrane, which is invariably associated with surface projections. As has been found with other myxoviruses, mumps virus replicates by budding from the cell surface. The virus particle, roughly spherical in shape, has a size ranging from 1,000 to 8,000 A. Filamentous forms are rarely observed in the present culture system. Ferritin-conjugated antibody specifically labels the cytoplasmic nucleoprotein, the modified cell membrane, and the virus particle. Intranuclear inclusions of low electron density and morphologically different from those described in measles virus-infected HeLa and amnion cells were observed in the nucleus of several infected cells. Immuno-electron microscopic observations suggest that the nucleoprotein synthesis rate exceeds that of cell membrane differentiation into viral envelope. This difference results in the accumulation of viral nucleoprotein in large intracytoplasmic masses which can be demonstrated by electron microscopy.

Duc-Nguyen, Huu(National Cancer Institute, Bethesda, Md.), Edith N. Rosenblum, and Robert F. Zeigel. Persistent infection of a rat kidney cell line with Rauscher murine leukemia virus. J. Bacteriol. 92:1133–1140. 1966.—The propagation of a murine leukemia virus (Rauscher) in a kidney cell line, derived from a rat with lymphoid leukemia, was studied. A complement-fixing (CF) antigen reacting with Rauscher immune sera was detected at various passage levels, which correlated with the visualization by use of electron microscopy of viral buds and viral particles in different stages of maturation in all passages. Five-month-old monolayers continued to shed virus and to yield high CF antigen titers. The cell-free supernatant fluid from cultures of the 14th passage was shown to be infectious for a normal rat kidney cell line, as evidenced by the appearance of the CF antigen in this line. Interferon production was not demonstrated in infected cultures. The overall data indicated that rat kidney cells could be used to propagate Rauscher virus in a carrier state.

Duc-Nguyen, Huu(The Children's Hospital of Philadelphia, Philadelphia, Pa.), and Werner Henle. Replication of mumps virus in human leukocyte cultures. J. Bacteriol. 92:258–265. 1966.—Human peripheral leukocyte cultures maintained in the presence of phytohemagglutinin (PHA) were found to support to some extent the replication of mumps virus. When such cultures were exposed, within 24 hr after their initiation, to a high input multiplicity of virus, successful infection, as determined by immunofluorescence and plaque assays, did not become evident before the 3rd or 4th day. On exposure of cultures 4 to 5 days old, viral replication was detectable within 2 days. In both instances, peak immunofluorescence and virus titers were reached when the cultures were 7 to 9 days old and composed mainly of blast forms. With decreasing input multiplicities of infection, cells containing viral antigen and production of infectious viral progeny became detectable with increasing delay. No significant viral replication was noted in surviving cells maintained in the absence of PHA. These results indicate that mainly, if not solely, the PHA-stimulated cells of the lymphocytic series support viral multiplication. The extent of the infectious process was limited, however, because the life span of the cultures was not significantly shortened, the yields of infectious virus per immunofluorescent cell were at all times low, and most infected cells contained only a few well-delineated small masses of antigen, suggestive of an abortive infection. Only fresh cultures were capable of synthesizing interferon on stimulation by mumps, Newcastle disease, or Sendai viruses. When the cultures were set up in the presence of PHA, this capacity was lost within 24 hr. PHA per sefailed to induce detectable production of an interferon under the conditions used. The implications of these findings are discussed.