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The ability of reconstituted, concentrated lyophilized lavage fluid to activate noninfectious Sendai virus (NISV) in vitro was examined. Lavage fluid was obtained from 4-ipomcanol (4-IP)-injured lungs at 1, 3, 5, 7, 9, and 13 days after treatment, and 1, 7, and 13 days after sham treatment (controls). Significantly higher viral titers were obtained using lavage fluid collected 1 day after 4-IP treatment. Higher protein concentrations were present in lavage fluid obtained at day 1 and 3 after 4-IP treatment. It is concluded that local viral-activating protease concentrations resulting from 4-IP-induced pulmonary injury is a likely microenvironmental modulator of paramyxoviral replication and can play an important role in paramyxoviral-induced lung injury.

Noncytocidal persistent infections at 37 C of mouse L cells (Lvsv) with infective B particles of vesicular stomatitis virus (VSV) could be established only in the presence of large numbers of defective interfering (DI) particles. Under these conditions, there was a rapid spontaneous selection of temperature-sensitive (ts) virus. At 10 days there was an increase to 17.8% in the frequency of ts clones in the virus population; by 17 days this frequency had reached 85.2%, and by 63 days 100% of the clones isolated were ts at 39.5 C, the nonpermissive temperature used. All 34 of the clones isolated from the 84-day fluid had an RNA-phenotype, and 8 clones that were tested all belonged to VSV complementation group I. When tested by an interference assay, Lvsv fluids did not contain significant numbers of DI particles (less than 1 DI/PFU). Furthermore, persistent infection of L cells at 37 C could be initiated under conditions in which few, if any, DI particles were present by using low input multiplicities (10(-4) and 10(-5) of a clonal isolate of an RNA-group I mutant obtained from Lvsv cells. On the basis of these and other results, a mechanism is proposed to explain the role of ts mutants in both the establishment and maintenance of the persistently infected state.

Purified defective interfering (DI) particles of vesicular stomatitis virus (VSV) inhibit the replication of a heterologous virus, pseudorabies virus (PSR), in hamster (BHK-21) and rabbit (RC-60) cell lines. In contrast to infectious B particles of VSV, UV irradiation of DI particles does not reduce their ability to inhibit PSR replication. However, UV irradiation progressively reduces the ability of DI particles to cause homologous interference with B particle replication. Pretreatment with interferon does not affect the ability of DI particles to inhibit PSR replication in a rabbit cell line (RC-60) in which RNA, but not DNA, viruses are sensitive to the action of interferon. Under similar conditions of interferon pretreatment, the inhibition of PSR by B particles is blocked. These data suggest that de novo VSV RNA or protein synthesis is not required for the inhibition of PSR replication by DI particles. DI particles that inhibit PSR replication also inhibit host RNA and protein synthesis in BHK-21 and RC-60 cells. Based on the results described and data in the literature, it is proposed that the same component of VSV B and DI particles is responsible for most, if not all, of the inhibitory activities of VSV, except homologous interference.

Infectious B particles of vesicular stomatitis virus (VSV) are capable of inhibiting the replication of pseudorabies virus (PSR) in a variety of cell lines. Even under conditions of an abortive infection in a continuous line of rabbit cornea cells (RC-6O), B particles interfere with the replication of PSR with high efficiency. Particle per cell dose-response analysis of B particle populations revealed that the number of VSV particles capable of inhibiting PSR replication exceeds the number of PFU by a factor of 32 to 64. When B particles are treated with UV irradiation, a drastic increase in the multiplicity of infection is required to inhibit PSR replication. Whereas one infective B particles per cell is sufficient to prevent replication of PSR, 800 to 1,000 VSV particles rendered noninfective by UV irradiation are required to compensate for the loss of VSV synthetic activity that results from irradiation. Temperature-sensitive mutants representing five complementation groups of VSV were tested at low multiplicities of infection for their effect on PSR replication at the nonpermissive temperature. Generally, the ability of the different complementation groups to amplify virion products at the nonpermissive temperature is associated with their ability to inhibit PSR replication. These results imply that at low multiplicities of infection, amplification of infecting VSV components is necessary for inhibition of PSR replication., but at high multiplicities of infection with VSV, a virion component can prevent PSR replication in the absence of de novo VSV RNA or protein synthesis.

The spectrum of respiratory syncytial virus-encoded proteins was examined in infected cell extracts by standard polyacrylamide gel electrophoresis and by two-dimensional gel analysis. Polyacrylamide gel electrophoresis analysis of a variety of respiratory syncytial virus-infected, actinomycin D-treated cell lines revealed the presence of as many as nine virus-encoded proteins. Seven of these nine proteins were immunoprecipitated by anti-respiratory syncytial serum. Only one major band of [3H]glucosamine was detected in infected cell extracts (Vp86), whereas the reported major virion glycoprotein (Vp48-53) was difficult to detect in infected cells when carbohydrate labels were employed. Two-dimensional gel analysis easily identified seven viral proteins, and one other was tentatively identified. The reported major virion glycoprotein again was not consistently detected. The results of this study confirm the existence of a virus-coded glycoprotein (Vp86) in infected cell extracts. The existence of this glycoprotein in the purified virion has been in dispute, but the apparent low methionine content of this protein may be the reason for this controversy.

A series of proteases of diverse substrate specificity were tested for their effect on respiratory syncytial virus-induced cytopathology. Three of the enzymes, thrombin, plasmin, and trypsin, were able to augment significantly the fusion of virus-infected A549 cells. On a concentration basis, thrombin was the most active promoter, followed by plasmin and then trypsin. Hirudin, a specific thrombin inhibitor, blocked the fusion-enhancing property of thrombin, yet had no influence on the basal rate of fusion in the absence of the enzyme. By contrast, the amidine-type inhibitors of trypsin-like proteases, bis(5-amidino-2-benzimidazolyl)-methane (BABIM), blocked not only the thrombin effect, but also the fusion in the thrombin-free controls. The suppressive activity of BABIM was observed at concentrations so low as to exclude any direct inhibitory effect on thrombin itself. These results make it seem very likely that thrombin advances cell fusion by activating a BABIM-sensitive protease. Plasmin and trypsin can be expected to act in a similar manner.

Seven calves between 1 week and 2 months of age were infected with a noncytopathic field isolate of bovine viral diarrhea virus (BDV) in order to evaluate the effect of BDV infection on the concentration of circulating platelets in the blood. All calves were determined to be free of BDV and neutralizing antibodies to BDV before infection. Platelet counts were performed on a daily basis over a 30-day period beginning at the time of infection. By 2 weeks postinfection, all calves showed a significant drop in the number of circulating platelets and a marked hyperplasia of megakaryocytes in the bone marrow. In three of the seven calves, thrombocytopenia was severe (less than or equal to 5,000/microliters) for 1 to 6 days. In two of these three animals, extensive petechial and ecchymotic hemorrhages were observed on all mucosal surfaces and on various internal organs during the period of severe thrombocytopenia. BDV was consistently isolated from the platelets during the early phases of the infection, and viral antigen was occasionally detected on platelets by a fluorescent-antibody assay. The results demonstrate that BDV infection is associated with decreases in platelet numbers and suggest that platelets may serve as carriers of circulating virus.

A panel of monoclonal antibodies that recognize the two major glycoproteins of bovine viral diarrhea virus (BDV) was used to evaluate the antigenic relationship between cytopathic (CP) and noncytopathic (NCP) viruses isolated from cattle dead or dying from fatal BDV infections. Various unrelated BDV isolates were initially screened by indirect immunofluorescence with monoclonal antibodies directed against the 56- to 58- and 48-kilodalton glycoproteins of the virus. A wide spectrum of reactivity that was independent of biotype was found. Biological clones of the same isolate showed only minor variations from the parental isolate, as did isolates taken from different animals located on the same farm. A similar analysis was repeated with pairs of CP and NCP viruses isolated from 16 unrelated clinical cases of BDV infection resulting in fatal disease. The reactivity patterns within individual pairs of isolates taken from the same animals were in most instances very similar and in some cases indistinguishable from one another. The results demonstrate that antigenic similarity between biotypes is a consistent finding in animals dying from fatal BDV infections. In view of the wide degree between biotypes is a consistent finding in animals dying from fatal BDV infections. In view of the wide degree of variation in reactivity patterns between unrelated BDV isolates, the close antigenic similarity of CP BDV to the homologous NCP BDV of a given pair strongly suggests that CP BDV arises by mutation from NCP BDV.