Host defense mechanisms against infectious bovine rhinotracheitis virus: in vitro stimulation of sensitized lymphocytes by virus antigen

Isolated peripheral blood lymphocytes (PBL) from cattle immunized or infected with infectious bovine rhinotracheitis (IBR) virus were cultured in vitro with ultraviolet light-inactivated IBR virus, and the degree of lymphocyte blastogenesis was quantitated by measurement of the uptake of [(3)H]thymidine into acid-insoluble material. Lymphocyte blastogenesis only occurred with PBL from immunized or infected animals. The optimal conditions for lymphocyte blastogenesis were defined. Blastogenesis was specific since cells from animals immunized against IBR failed to react with two other herpesvirus antigens tested, herpes simplex and equine rhinopneumonitis viruses. Blastogenesis could be prevented by reacting IBR antigen with IBR-specific antibody before adding to cultures, but incorporating IBR-specific antibody in the culture medium after adding free antigen failed to inhibit blastogenesis. With intranasally infected animals, lymphocyte blastogenesis was detectable after 5 days, reached peak levels between days 7 and 10, and then declined to low levels by day 19. In contrast, levels of neutralizing antibody were barely detectable on day 7 and reached maximal concentrations on day 19. The lymphocyte blastogenesis assay was emphasized as a convenient and useful in vitro correlate of cell-mediated immunity that should help define the role of cell-mediated immunity in immunity to herpesviruses.

Inhibition of polyoma virus development in mouse-hamster heterokaryons

Mouse cells which normally permitted polyoma virus development, and hamster cells which were non-permissive (BHK-21 and polyoma virus-transformed hamster cells), were subjected to cell-fusion techniques, and the resultant cultures were examined for the capacity of heterokaryons to yield polyoma viral capsid protein. Little or no capsid protein was synthesized in the heterokaryons, although individual mouse cells and mouse homokaryons gave normal yields. Furthermore, the hamster cell inhibitory effect manifested itself even when the mouse cells had been infected with the virus before cell fusion.

Cell-fusion properties of Sendai virus prepared by polyethylene-glycol precipitation

Sendai virus was concentrated from the allantoic fluid of embryonated chicken eggs by polyethyleneglycol (PEG) precipitation. A concentration of 6–8% PEG sufficed to precipitate essentially all of the virus (measured by hemagglutination) with maximum retention of cell-fusion ability. Electron-microscopic examination of the 6% PEG pellet revealed only intact virions. Thus the method is suitable for preparing Sendai virus for cell-fusion experiments.

Properties of polyoma virus transformed cells. I. Oncogenic properties

Studies were made on the oncogenic properties of a line of polyoma virus transformed hamster cells. Passage of the cells in vivo resulted in an increase in oncogenicity. Thus the latent period for the appearance of a tumor was decreased, and as few as 5 to 10 cells were now sufficient to produce a tumor in a young hamster. Tumors were invariably restricted to the subcutaneous site of injection. In contrast, polyoma virus itself caused widespread production of tumors throughout the animal. Histological examination of tumor tissue revealed marked differences between tumors caused by virus or virus-transformed cells. It was concluded that little or no metastasis of transformed cells could have occurred, and that insignificant rescue of the polyoma virus genome must have been induced in transformed cell tumors.Powassan virus, a group B arbovirus, did not show any oncolytic activity toward tumors induced by the polyoma virus transformed cells.

The use of fluorescein isothiocyanate in the determination of the bacterial biomass of grassland soil

Quantitative recoveries of bacteria added to a number of soils were obtained using fluorescein isothiocyanate (FITC) as a stain. Enzyme fluorescence, using fluorescein diacetate or dibutyrate, could not be adapted for the routine counting of metabolizing organisms in soil. Staining with rose bengal gave recoveries of 60–80%.Soil-extract dilution plates revealed 4 × 107 bacteria/g in the 0–10 cm layer in April and 27 × 107 in October. One-third of this number was observed in the 20–30 cm layer. Actinomycete colonies added another 20% to the counts at the 0–30 cm depth but constituted 70% of the total colonies from the 90–120 cm depth. Microscopic counts indicated 2.2–4.6 × 109 organisms/g of surface soil. The number of bacteria decreased in a linear fashion with depth but no relation was found between the numbers obtained by direct microscopy and those by plate counting. However, each of the methods showed a high relationship between the size of the bacterial population present at each depth on the different sampling dates.The observed bacteria, actinomycete spores, and hyphal segments averaged 0.6 × 1 μ. On this basis, the biomass in the top 30 cm, as determined by direct microscopy, ranged from 30 to 76 g/m2 (dry weight basis). This implies, considering the amount of available energy, that the individual cells have enough energy to divide only a few times each year. Direct microscopic counting yields a quantitative picture of the organisms present but cannot separate between inactive cells, spores, and metabolizing organisms. Data from plate counts probably give a truer indication of metabolically active cells.